1. |
- Ahlberg, Erik, et al.
(author)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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In: Dagens nyheter (DN debatt). - 1101-2447.
-
Journal article (pop. science, debate, etc.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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2. |
- Kehoe, Laura, et al.
(author)
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Make EU trade with Brazil sustainable
- 2019
-
In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Journal article (other academic/artistic)
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3. |
- Stenseke, Marie, et al.
(author)
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Kris i naturen – vår existens har blivit sårbar
- 2019
-
In: Svenska Dagbladet, Stockholm. - 1101-2412.
-
Journal article (pop. science, debate, etc.)abstract
- Fler arter än någonsin i mänsklighetens historia hotas av utrotning och den biologiska mångfalden lokalt har förändrats kraftigt i en stor del av världens ekosystem. Grundläggande förändringar behövs både i samhället och för individer, för att bromsa den negativa trenden, skriver en rad debattörer.
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4. |
- Adolfsson, Lisa, 1984, et al.
(author)
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Mycorrhiza Symbiosis Increases the Surface for Sunlight Capture in Medicago truncatula for Better Photosynthetic Production
- 2015
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:1
-
Journal article (peer-reviewed)abstract
- Arbuscular mycorrhizal (AM) fungi play a prominent role in plant nutrition by supplying mineral nutrients, particularly inorganic phosphate (Pi), and also constitute an important carbon sink. AM stimulates plant growth and development, but the underlying mechanisms are not well understood. In this study, Medicago truncatula plants were grown with Rhizophagus irregularis BEG141 inoculum (AM), mock inoculum (control) or with Pi fertilization. We hypothesized that AM stimulates plant growth through either modifications of leaf anatomy or photosynthetic activity per leaf area. We investigated whether these effects are shared with Pi fertilization, and also assessed the relationship between levels of AM colonization and these effects. We found that increased Pi supply by either mycorrhization or fertilization led to improved shoot growth associated with increased nitrogen uptake and carbon assimilation. Both mycorrhized and Pi-fertilized plants had more and longer branches with larger and thicker leaves than the control plants, resulting in an increased photosynthetically active area. AM-specific effects were earlier appearance of the first growth axes and increased number of chloroplasts per cell section, since they were not induced by Pi fertilization. Photosynthetic activity per leaf area remained the same regardless of type of treatment. In conclusion, the increase in growth of mycorrhized and Pi-fertilized Medicago truncatula plants is linked to an increase in the surface for sunlight capture, hence increasing their photosynthetic production, rather than to an increase in the photosynthetic activity per leaf area.
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5. |
- af Ekenstam, Angelica, et al.
(author)
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Leaf respiration rates are increased by warm season as well as by elevated temperature treatment in Eucalyptus globulus
- 2014
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In: EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria.
-
Conference paper (other academic/artistic)abstract
- Plant leaf respiration is one of the major CO2 fluxes between terrestrial biosphere and the atmosphere, and its responses to elevated CO2 and temperature thus have important implications for the carbon cycle and rate on ongoing climate change. Non-photorespiratory leaf respiration is reduced in light, Rlight, compared with the rate in the dark, Rdark. It is therefore important to consider both Rlight and Rdark when estimating the exchange of CO2 between the biosphere and the atmosphere, during current and future climates. This study was conducted at the Hawkesbury Forest Experiment, HFE, in Richmond, NSW, Australia. Trees of Tasmanian Blue Gum (Eucalyptus globulus Labill.) were exposed in whole tree chambers (WTC) to a complete factorial combination of ambient and elevated temperature and CO2 (+3 °C and +240 ppm CO2, respectively). The measurements of Rlight and Rdark were made in 2011 after 15 month exposure in the WTCs. The measurements were made in March (after the year’s hottest months) and October (after the coldest period). Rlight was determined at four temperatures ranging between 20 and 40 °C on attached leaves using a portable gas exchange system (LI-6400XT). Rdark was measured at 20-40 °C in October and at 25 °C in March. Rdark was measured after dark acclimation for at least 30 min and Rlight was determined from the intersection of the photosynthetic CO2 responses measured at three different light intensities using the Laisk metod. Trees grown in elevated temperature had a considerably higher Rdark (+53% across all measurement temperatures in October). However, Rlight did not respond significantly to either CO2 or temperature. In October, the Rlight to Rdark ratio indicated an overall light inhibition of respiration of 31% across all temperatures and in March the light inhibition was 22 % at 25 °C. The seasonal comparisons showed that both Rlight and Rdark were considerably higher after the warm compared to cold season, especially when measured at high temperature. These results points out the importance to account for Rlight as well as seasonal thermal respiratory acclimation when improving predictions of the carbon exchange between tree canopies and the atmosphere. If not taking light inhibition into account, leaf respiration is being overestimated and if not taking the seasonal acclimation into account the errors are potentially very large.
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6. |
- Alfonsson, Sven, 1977-, et al.
(author)
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Differences in motivation and adherence to a prescribed assignment after face-to-face and online psychoeducation : A randomized experiment
- 2017
-
In: BMC Psychology. - : Springer Science and Business Media LLC. - 2050-7283. ; 5:1
-
Journal article (peer-reviewed)abstract
- Background: Adherence to treatment homework is associated with positive outcomes in behavioral psychotherapy but compliance to assignments is still often moderate. Whether adherence can be predicted by different types of motivation for the task and whether motivation plays different roles in face-to-face compared to online psychotherapy is unknown. If models of motivation, such as Self-determination theory, can be used to predict patients’ behavior, it may facilitate further research into homework promotion. The aims of this study were, therefore, to investigate whether motivation variables could predict adherence to a prescribed assignment in face-to-face and online interventions using a psychotherapy analog model. Methods: A total of 100 participants were included in this study and randomized to either a face-to-face or online intervention. Participants in both groups received a psychoeducation session and were given an assignment for the subsequent week. The main outcome measurements were self-reported motivation and adherence to the assignment. Results: Participant in the face-to-face condition reported significantly higher levels of motivation and showed higher levels of adherence compared to participants in the online condition. Adherence to the assignment was positively associated with intrinsic motivation and intervention credibility in the whole sample and especially in the online group. Conclusions: This study shows that intrinsic motivation and intervention credibility are strong predictors of adherence to assignments, especially in online interventions. The results indicate that intrinsic motivation may be partly substituted with face-to-face contact with a therapist. It may also be possible to identify patients with low motivation in online interventions who are at risk of dropping out. Methods for making online interventions more intrinsically motivating without increasing external pressure are needed.
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7. |
- Aloysie, Manishimwe, et al.
(author)
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Warming Responses of Leaf Morphology Are Highly Variable among Tropical Tree Species
- 2022
-
In: Forests. - : MDPI AG. - 1999-4907. ; 13:2
-
Journal article (peer-reviewed)abstract
- Leaf morphological traits vary along climate gradients, but it is currently unclear to what extent this results from acclimation rather than adaptation. Knowing so is important for predicting the functioning of long-lived organisms, such as trees, in a rapidly changing climate. We investigated the leaf morphological warming responses of 18 tropical tree species with early (ES) abd late (LS) successional strategies, planted at three sites along an elevation gradient from 2400 m a.s.l. (15.2 °C mean temperature) to 1300 m a.s.l. (20.6 °C mean temperature) in Rwanda. Leaf size expressed as leaf area (LA) and leaf mass per area (LMA) decreased, while leaf width-to-length ratio (W/L) increased with warming, but only for one third to half of the species. While LA decreased in ES species, but mostly not in LS species, changes in LMA and leaf W/L were common in both successional groups. ES species had lower LMA and higher LA and leaf W/L compared to LS species. Values of LMA and LA of juvenile trees in this study were mostly similar to corresponding data on four mature tree species in another elevation-gradient study in Rwanda, indicating that our results are applicable also to mature forest trees. We conclude that leaf morphological responses to warming differ greatly between both successional groups and individual species, with potential consequences for species competitiveness and community composition in a warmer climate. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
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8. |
- Barth, Sabine, 1974, et al.
(author)
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Water-Use-Efficiency of Forests Exposed to Elevated Carbon Dioxide and/or Elevated Tropospheric Ozone
- 2009
-
In: 8th International Carbon Dioxide Conference, Jena Germany, 13-19 September 2009.
-
Conference paper (other academic/artistic)abstract
- Effects of a 40-50% increase of ambient CO2 and O3, alone and in combination, on pure aspen and mixed aspen-birch forests were examined in the free air CO2-O3 enrichment experiment near Rhinelander, Wisconsin, USA (Aspen FACE). These atmospheric conditions represent the prediction for 2050. Trees exposed to elevated CO2 showed a significant increase in tree size, leave area index (LAI) and fine root production, while elevated O3 reduced tree size and LAI but not fine root biomass after 7 years of exposure (King et al. 2005). Measurements of sap flux and yearly stem wood production were made in 2004 and 2006, after >6 years of experimental treatments and after steady-state LAI had been reached. Water use efficiency (WUE) was determined as a function of yearly stem wood production and sap flux during the active growing seasons, between DOY 168-249.
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9. |
- Broberg, Malin, 1989, et al.
(author)
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Effects of ozone, drought and heat stress on wheat yield and grain quality
- 2023
-
In: Agriculture, Ecosystems & Environment. - 0167-8809. ; 352:15
-
Journal article (peer-reviewed)abstract
- Tropospheric ozone (O3) is a gaseous phytotoxic plant stressor known to reduce wheat (Triticum aestivum) crop yields at current concentrations. O3 is predicted to increase in many crop-growing regions, together with higher frequencies of heatwaves and droughts. In this study, wheat crops were exposed to two levels of O3 (ambient and ~70 ppb) in combination with ambient or elevated temperature (+8 ◦C) and two watering regimes (well-watered and 50% reduced water supply) during the grain-filling period. With this experimental setup, we assessed the interactive effects between O3, temperature and water supply on wheat yield and grain quality, and measured leaf gas exchange to explore the underlying mechanisms. Overall, O3, warming and drought all decreased grain yield and average grain mass but increased grain concentration of N and other nutrient elements. Increasing daytime O3 from 25 to 73 ppb resulted in a 25% yield reduction in treatments with ambient temperature and well-watered soil. Drought reduced the impact of O3 on light-saturated photosynthesis, grain mass, total aboveground biomass and grain concentrations of K, Ca, Mg, Mo. In contrast, concentrations of K and Ca increased to a larger extent when O3 stress was combined with elevated temperature. Grain concentrations of N, Ca and Zn were closely and negatively related to grain yield regardless of O3, heat and drought stress, likely explained by the reduction in grain filling period, with starch accumulation reduced to a larger extent than that of these elements. P, K, Mg, Mn, Mo concentrations were weakly related to grain yield, but were clearly altered by environmental stress. The modifying effect of water availability is crucial to include in assessments of O3 impacts on global food production in relation to climate change, considering effects on wheat yield variables and grain nutrient concentrations.
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10. |
- Broberg, Malin, 1989, et al.
(author)
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Fertilizer efficiency in wheat is reduced by ozone pollution
- 2017
-
In: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 607-608, s. 876-880
-
Journal article (peer-reviewed)abstract
- Inefficient use of fertilizers by crops increases the risk of nutrient leaching from agro-ecosystems, resulting in economic loss and environmental contamination. We investigated how ground-level ozone affects the efficiency by which wheat used applied nitrogen (N) fertilizer to produce grain protein (NE P , N efficiency with respect to protein yield) and grain yield (NE Y , N efficiency with respect to grain yield) across a large number of open-top chamber field experiments. Our results show significant negative ozone effects on NE P and NE Y , both for a larger data set obtained from data mining (21 experiments, 70 treatments), and a subset of data for which stomatal ozone flux estimates were available (7 experiments, 22 treatments). For one experiment, we report new data on N content of different above-ground plant fractions as well as grain K and P content. Our analysis of the combined dataset demonstrates that the grain yield return for a certain investment in N fertilizer is reduced by ozone. Results from the experiment with more detailed data further show that translocation of accumulated N from straw and leaves to grains is significantly and negatively affected by ozone, and that ozone decreases fertilizer efficiency also for K and P. As a result of lower N fertilization efficiency, ozone causes a risk of increased N losses from agroecosystems, e.g. through nitrate leaching and nitrous oxide emissions, a hitherto neglected negative effect of ozone. This impact of ozone on the N cycle implies that society is facing a dilemma where it either (i) accepts increased N pollution and counteracts ozone-induced yield reductions by increasing fertilization or (ii) counteracts N pollution under elevated ozone by reducing fertilization, accepting further yield loss adding to the direct effect of ozone on yield.
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11. |
- Buker, P, et al.
(author)
-
Comparison of different stomatal conductance algorithms for ozone flux modelling
- 2005
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In: UNECE – Workshop “Critical Levels of Ozone: Further applying and developing the flux-based concept”, Obergurgl, 15-19 November 2005.
-
Conference paper (other academic/artistic)abstract
- Two widely used algorithms for modelling stomatal conductance (gs) were compared in order to evaluate the approach leading to the most realistic predictions of stomatal fluxes to vegetated surfaces: a multiplicative algorithm initially developed by Jarvis (1976) and refined by Emberson et al. (2000) (DO3SE ) and a photosynthesis-based Ball&Berry-type algorithm developed by Nikolov et al. (1995) (LEAFC3). Both models were parameterised for several crop and tree species (wheat, grapevine, Scots pine, beech and birch) and have been applied to various datasets – with the main focus on wheat - representing different European regions (North, Central and South Europe). A sensitivity analysis has been carried out for both models to evaluate the dependence of gs on the meteorological parameters temperature, photosynthetic active radiation and vapour pressure deficit. Furthermore, in order to test whether a general species-specific parameterisation can account for differences in gs due to plants growing under different climatic conditions throughout Europe, the models have been re-parameterised for local meteorological conditions. A direct comparison of both models showed that the net photosynthetic-based model required more detailed meteorological (e.g. ambient CO2-concentration, dew-point temperature) and plant-physiological (e.g. Vcmax and Jmax) input parameters while not delivering a substantially higher R2 when comparing measured and modelled gs. The relative weakness of the multiplicative model lies in its dependence on the maximum stomatal conductance (gmax), whereas the photosynthesis-based model is not taking into account phenology-related changes in gs. Furthermore, the results show that an equally close relationship between gs and net photosynthetic rate throughout the entire growing season is questionable. We conclude that the multiplicative approach is favourable for calculating stomatal fluxes on a wider scale (e.g. within EMEP-deposition model), whereas the photosynthesis-based approach is a potential alternative for modelling fluxes on a local scale.
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12. |
- Buker, P., et al.
(author)
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DO3SE modelling of soil moisture to determine ozone flux to forest trees
- 2012
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In: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:12, s. 5537-5562
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Journal article (peer-reviewed)abstract
- The DO3SE (Deposition of O-3 for Stomatal Exchange) model is an established tool for estimating ozone (O-3) deposition, stomatal flux and impacts to a variety of vegetation types across Europe. It has been embedded within the EMEP (European Monitoring and Evaluation Programme) photochemical model to provide a policy tool capable of relating the flux-based risk of vegetation damage to O-3 precursor emission scenarios for use in policy formulation. A key limitation of regional flux-based risk assessments has been the assumption that soil water deficits are not limiting O-3 flux due to the unavailability of evaluated methods for modelling soil water deficits and their influence on stomatal conductance (g(sto)), and subsequent O-3 flux. This paper describes the development and evaluation of a method to estimate soil moisture status and its influence on g(sto) for a variety of forest tree species. This DO3SE soil moisture module uses the Penman-Monteith energy balance method to drive water cycling through the soil-plant-atmosphere system and empirical data describing g(sto) relationships with pre-dawn leaf water status to estimate the biological control of transpiration. We trial four different methods to estimate this biological control of the transpiration stream, which vary from simple methods that relate soil water content or potential directly to g(sto), to more complex methods that incorporate hydraulic resistance and plant capacitance that control water flow through the plant system. These methods are evaluated against field data describing a variety of soil water variables, g(sto) and transpiration data for Norway spruce (Picea abies), Scots pine (Pinus sylvestris), birch (Betula pendula), aspen (Populus tremuloides), beech (Fagus sylvatica) and holm oak (Quercus ilex) collected from ten sites across Europe and North America. Modelled estimates of these variables show consistency with observed data when applying the simple empirical methods, with the timing and magnitude of soil drying events being captured well across all sites and reductions in transpiration with the onset of drought being predicted with reasonable accuracy. The more complex methods, which incorporate hydraulic resistance and plant capacitance, perform less well, with predicted drying cycles consistently underestimating the rate and magnitude of water loss from the soil. A sensitivity analysis showed that model performance was strongly dependent upon the local parameterisation of key model drivers such as the maximum g(sto), soil texture, root depth and leaf area index. The results suggest that the simple modelling methods that relate g(sto) directly to soil water content and potential provide adequate estimates of soil moisture and influence on g(sto) such that they are suitable to be used to assess the potential risk posed by O-3 to forest trees across Europe.
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13. |
- Büker, P, et al.
(author)
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New flux based doseeresponse relationships for ozone for European forest tree species
- 2015
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 206, s. 163-174
-
Journal article (peer-reviewed)abstract
- To derive O3 doseeresponse relationships (DRR) for five European forest trees species and broadleaf deciduous and needleleaf tree plant functional types (PFTs), phytotoxic O3 doses (PODy) were related to biomass reductions. PODy was calculated using a stomatal flux model with a range of cut-off thresholds (y) indicative of varying detoxification capacities. Linear regression analysis showed that DRR for PFT and individual tree species differed in their robustness. A simplified parameterisation of the flux model was tested and showed that for most non-Mediterranean tree species, this simplified model led to similarly robust DRR as compared to a species- and climate region-specific parameterisation. Experimentally induced soil water stress was not found to substantially reduce PODy, mainly due to the short duration of soil water stress periods. This study validates the stomatal O3 flux concept and represents a step forward in predicting O3 damage to forests in a spatially and temporally varying climate.
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14. |
- Carroll, M. A., et al.
(author)
-
Reactive nitrogen oxide fluxes to a mixed hardwood forest
- 2008
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In: International Geosphere-Biosphere Programme, Congress in May 2008.
-
Conference paper (other academic/artistic)abstract
- Measurements of NOx (nitric oxide and nitrogen dioxide) mixing ratios and fluxes (20 May – 1 September) and NOy mixing ratios and fluxes (9 August – 1 September) were made at a northern mixed hardwood forest located at the University of Michigan Biological Station in northern Michigan, USA (45.5 deg N, 84.7 deg W, elevation 238 m) in 2005. During the 15-week period of NOx measurements, the site received flow from two dominant flow regimes: the north-northwest (ozone 20 – 40 ppbv) and the south-southwest (ozone 40 – 100 ppbv) approximately 26% and 27% of the time, respectively. Typical ambient NOx and NOy levels ranged from 0.5 – 2.4 ppbv and 0.5 to 3 ppbv, respectively. NO and NOy fluxes were found to be strongly diurnal with mid-day maximum downward fluxes of 0.5 – 2 and 1 – 2 μmole per square meter per hour, respectively, and nighttime fluxes at or near zero. In contrast, NO2 fluxes were small and upward during the morning, small and downward during the afternoon, and at or near zero at night. NOx fluxes were found to be essentially zero throughout the day and night. If all of the NOy deposition in this study were in the form of nitric acid, it would increase the available nutrient nitrate input to the forest by 8% over measured wet nitrate deposition.
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15. |
- Clifton, O. E., et al.
(author)
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Influence of Dynamic Ozone Dry Deposition on Ozone Pollution
- 2020
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In: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 125:8
-
Journal article (peer-reviewed)abstract
- Identifying the contributions of chemistry and transport to observed ozone pollution using regional-to-global models relies on accurate representation of ozone dry deposition. We use a recently developed configuration of the NOAA GFDL chemistry-climate model - in which the atmosphere and land are coupled through dry deposition-to investigate the influence of ozone dry deposition on ozone pollution over northern midlatitudes. In our model, deposition pathways are tied to dynamic terrestrial processes, such as photosynthesis and water cycling through the canopy and soil. Small increases in winter deposition due to more process-based representation of snow and deposition to surfaces reduce hemispheric-scale ozone throughout the lower troposphere by 5-12 ppb, improving agreement with observations relative to a simulation with the standard configuration for ozone dry deposition. Declining snow cover by the end of the 21st-century tempers the previously identified influence of rising methane on winter ozone. Dynamic dry deposition changes summer surface ozone by -4 to +7 ppb. While previous studies emphasize the importance of uptake by plant stomata, new diagnostic tracking of depositional pathways reveals a widespread impact of nonstomatal deposition on ozone pollution. Daily variability in both stomatal and nonstomatal deposition contribute to daily variability in ozone pollution. Twenty-first century changes in summer deposition result from a balance among changes in individual pathways, reflecting differing responses to both high carbon dioxide (through plant physiology versus biomass accumulation) and water availability. Our findings highlight a need for constraints on the processes driving ozone dry deposition to test representation in regional-to-global models.
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16. |
- Coste, S, et al.
(author)
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Assessing foliar chlorophyll contents with the SPAD-502 chlorophyll meter: 165 a calibration test with thirteen tree species of tropical rainforest in French Guiana
- 2010
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In: Annals of Forest Science. - 1286-4560. ; 67:6
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Journal article (peer-reviewed)abstract
- • Chlorophyll meters such as the SPAD-502 offer a simple, inexpensive and rapid method to estimate foliar chlorophyll content. However, values provided by SPAD-502 are unitless and require empirical calibrations between SPAD units and extracted chlorophyll values. • Leaves of 13 tree species from the tropical rain forest in French Guiana were sampled to select the most appropriate calibration model among the often-used linear, polynomial and exponential models, in addition to a novel homographic model that has a natural asymptote. • The homographic model best accurately predicted total chlorophyll content (µg cm-2) from SPAD units (R² = 0.89). Inter-specific differences in the homographic model parameters explain less than 7% of the variation in chlorophyll content in our dataset. • The utility of the general homographic model for a variety of research and management applications clearly outweighs the slight loss of model accuracy due to the abandon of the species-effect.
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17. |
- Cox, A. J. F., et al.
(author)
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Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change
- 2023
-
In: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 238:6, s. 2329-2344
-
Journal article (peer-reviewed)abstract
- Climate warming is causing compositional changes in Andean tropical montane forests (TMFs). These shifts are hypothesised to result from differential responses to warming of cold- and warm-affiliated species, with the former experiencing mortality and the latter migrating upslope. The thermal acclimation potential of Andean TMFs remains unknown. Along a 2000m Andean altitudinal gradient, we planted individuals of cold- and warm-affiliated species (under common soil and irrigation), exposing them to the hot and cold extremes of their thermal niches, respectively. We measured the response of net photosynthesis (A(net)), photosynthetic capacity and leaf dark respiration (R-dark) to warming/cooling, 5 months after planting. In all species, A(net) and photosynthetic capacity at 25 degrees C were highest when growing at growth temperatures (T-g) closest to their thermal means, declining with warming and cooling in cold-affiliated and warm-affiliated species, respectively. When expressed at T-g, photosynthetic capacity and Rdark remained unchanged in cold-affiliated species, but the latter decreased in warm-affiliated counterparts. R-dark at 25 degrees C increased with temperature in all species, but remained unchanged when expressed at T-g. Both species groups acclimated to temperature, but only warm-affiliated species decreased R-dark to photosynthetic capacity ratio at T-g as temperature increased. This could confer them a competitive advantage under future warming.
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18. |
- Crous, K. Y., et al.
(author)
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Temperature responses of photosynthesis and respiration in evergreen trees from boreal to tropical latitudes
- 2022
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In: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 234:2, s. 353-374
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Journal article (peer-reviewed)abstract
- Evergreen species are widespread across the globe, representing two major plant functional forms in terrestrial models. We reviewed and analysed the responses of photosynthesis and respiration to warming in 101 evergreen species from boreal to tropical biomes. Summertime temperatures affected both latitudinal gas exchange rates and the degree of responsiveness to experimental warming. The decrease in net photosynthesis at 25 degrees C (A(net25)) was larger with warming in tropical climates than cooler ones. Respiration at 25 degrees C (R-25) was reduced by 14% in response to warming across species and biomes. Gymnosperms were more sensitive to greater amounts of warming than broadleaved evergreens, with A(net25) and R-25 reduced c. 30-40% with > 10 degrees C warming. While standardised rates of carboxylation (V-cmax25) and electron transport (J(max25)) adjusted to warming, the magnitude of this adjustment was not related to warming amount (range 0.6-16 degrees C). The temperature optimum of photosynthesis (T-optA) increased on average 0.34 degrees C per degrees C warming. The combination of more constrained acclimation of photosynthesis and increasing respiration rates with warming could possibly result in a reduced carbon sink in future warmer climates. The predictable patterns of thermal acclimation across biomes provide a strong basis to improve modelling predictions of the future terrestrial carbon sink with warming.
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19. |
- Crouse, Kristine, et al.
(author)
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Acclimation of light and dark respiration to experimental and seasonal warming are mediated by changes in leaf nitrogen in Eucalyptus globulus
- 2017
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In: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 37:8, s. 1069-1083
-
Journal article (peer-reviewed)abstract
- Quantifying the adjustments of leaf respiration in response to seasonal temperature variation and climate warming is crucial because carbon loss from vegetation is a large but uncertain part of the global carbon cycle. We grew fast-growing Eucalyptus globulus Labill. trees exposed to +3 °C warming and elevated CO2 in 10-m tall whole-tree chambers and measured the temperature responses of leaf mitochondrial respiration, both in light (RLight) and in darkness (RDark), over a 20–40 °C temperature range and during two different seasons. RLight was assessed using the Laisk method. Respiration rates measured at a standard temperature (25 °C – R25) were higher in warm-grown trees and in the warm season, related to higher total leaf nitrogen (N) investment with higher temperatures (both experimental and seasonal), indicating that leaf N concentrations modulated the respiratory capacity to changes in temperature. Once differences in leaf N were accounted for, there were no differences in R25 but the Q10 (i.e., short-term temperature sensitivity) was higher in late summer compared with early spring. The variation in RLight between experimental treatments and seasons was positively correlated with carboxylation capacity and photorespiration. RLight was less responsive to short-term changes in temperature than RDark, as shown by a lower Q10 in RLight compared with RDark. The overall light inhibition of R was ∼40%. Our results highlight the dynamic nature of leaf respiration to temperature variation and that the responses of RLight do not simply mirror those of RDark. Therefore, it is important not to assume that RLight is the same as RDark in ecosystem models, as doing so may lead to large errors in predicting plant CO2 release and productivity.
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20. |
- De Kauwe, M. G., et al.
(author)
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A test of the ‘one-point method’ for estimating maximum carboxylation capacity from field-measured, light-saturated photosynthesis
- 2016
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In: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 210:3, s. 1130-1144
-
Journal article (peer-reviewed)abstract
- Simulations of photosynthesis by terrestrial biosphere models typically need a specification of the maximum carboxylation rate (Vcmax). Estimating this parameter using A–Ci curves (net photosynthesis, A, vs intercellular CO2 concentration, Ci) is laborious, which limits availability of Vcmax data. However, many multispecies field datasets include net photosynthetic rate at saturating irradiance and at ambient atmospheric CO2 concentration (Asat) measurements, from which Vcmax can be extracted using a ‘one-point method’. We used a global dataset of A–Ci curves (564 species from 46 field sites, covering a range of plant functional types) to test the validity of an alternative approach to estimate Vcmax from Asat via this ‘one-point method’. If leaf respiration during the day (Rday) is known exactly, Vcmax can be estimated with an r2 value of 0.98 and a root-mean-squared error (RMSE) of 8.19 μmol m−2 s−1. However, Rday typically must be estimated. Estimating Rday as 1.5% of Vcmax, we found that Vcmax could be estimated with an r2 of 0.95 and an RMSE of 17.1 μmol m−2 s−1. The one-point method provides a robust means to expand current databases of field-measured Vcmax, giving new potential to improve vegetation models and quantify the environmental drivers of Vcmax variation.
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21. |
- Dusenge, Mirindi Eric, 1986, et al.
(author)
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Limited thermal acclimation of photosynthesis in tropical montane tree species
- 2021
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 27:19, s. 4860-4878
-
Journal article (peer-reviewed)abstract
- The temperature sensitivity of physiological processes and growth of tropical trees remains a key uncertainty in predicting how tropical forests will adjust to future climates. In particular, our knowledge regarding warming responses of photosynthesis, and its underlying biochemical mechanisms, is very limited. We grew seedlings of two tropical montane rainforest tree species, the early-successional species Harungana montana and the late-successional species Syzygium guineense, at three different sites along an elevation gradient, differing by 6.8℃ in daytime ambient air temperature. Their physiological and growth performance was investigated at each site. The optimum temperature of net photosynthesis (ToptA) did not significantly increase in warm-grown trees in either species. Similarly, the thermal optima (ToptV and ToptJ) and activation energies (EaV and EaJ) of maximum Rubisco carboxylation capacity (Vcmax) and maximum electron transport rate (Jmax) were largely unaffected by warming. However, Vcmax, Jmax and foliar dark respiration (Rd) at 25℃ were significantly reduced by warming in both species, and this decline was partly associated with concomitant reduction in total leaf nitrogen content. The ratio of Jmax/Vcmax decreased with increasing leaf temperature for both species, but the ratio at 25℃ was constant across sites. Furthermore, in H. montana, stomatal conductance at 25℃ remained constant across the different temperature treatments, while in S. guineense it increased with warming. Total dry biomass increased with warming in H. montana but remained constant in S. guineense. The biomass allocated to roots, stem and leaves was not affected by warming in H. montana, whereas the biomass allocated to roots significantly increased in S. guineense. Overall, our findings show that in these two tropical montane rainforest tree species, the capacity to acclimate the thermal optimum of photosynthesis is limited while warming-induced reductions in respiration and photosynthetic capacity rates are tightly coupled and linked to responses of leaf nitrogen.
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22. |
- Dusenge, Mirindi Eric, 1986, et al.
(author)
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Photosynthetic capacities of mature tropical forest trees in Rwanda are linked to successional group identity rather than to leaf nutrient content
- 2014
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In: EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria.
-
Conference paper (other academic/artistic)abstract
- Tropical forests are crucial in the global carbon balance, yet information required to estimate how much carbon that enter these ecosystems through photosynthesis is very limited, in particular for Africa and for tropical montane forests. In order to increases the knowledge of natural variability of photosynthetic capacities in tropical tree species in tropical Africa, measurements of leaf traits and gas exchange were conducted on sun and shade leaves of ten tree species growing in two tropical forests in Rwanda in central Africa. Seven species were studied in Ruhande Arboretum, a forest plantation at mid altitude (ca 1700 m), and six species in Nyungwe National Park, a cooler and higher altitude (at ca 2500 m) montane rainforest. Three species were common to both sites. At Nyungwe, three species each belonged to the successional groups pioneer and climax species. Climax species had considerably lower maximum rates of photosynthetic carboxylation (Vcmax) and electron transport (Jmax) than pioneer species. This difference was not related to leaf nutrient content, but rather seemed to be caused by differences in within-leaf N allocation between the two successional groups. With respect to N, leaves of climax species invested less N into photosynthetic enzymes (as judged by lower Vcmax and Jmax values) and more N into chlorophyll (as judged by higher SPAD values). Photosynthetic capacities, (i.e., Jmax and Vcmax), Jmax:Vcmax ratio and P content were significantly higher in Nyungwe than in Arboretum. Sun leaves had higher photosynthetic capacities and nutrient content than shade leaves. Across the entire dataset, variation in photosynthetic capacities among species was not related to leaf nutrient content, although significant relationships were found within individual species. This study contributes critical tropical data for global carbon models and suggests that, for montane rainforest trees of different functional types, successional group identity is a better predictor of photosynthetic capacities than leaf nutrient content.
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23. |
- Dusenge, Mirindi Eric, 1986, et al.
(author)
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Photosynthetic capacity of tropical montane tree species in relation to leaf nutrients, successional strategy and growth temperature
- 2015
-
In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 177:4, s. 1183-1194
-
Journal article (peer-reviewed)abstract
- Photosynthetic capacity of tree leaves is typically positively related to nutrient content and little affected by changes in growth temperature. These relationships are, however, often poorly supported for tropical trees, for which interspecific differences may be more strongly controlled by within-leaf nutrient allocation than by absolute leaf nutrient content, and little is known regarding photosynthetic acclimation to temperature. To explore the influence of leaf nutrient status, successional strategy and growth temperature on the photosynthetic capacity of tropical trees, we collected data on photosynthetic, chemical and morphological leaf traits of ten tree species in Rwanda. Seven species were studied in a forest plantation at mid-altitude (~1,700 m), whereas six species were studied in a cooler montane rainforest at higher altitude (~2,500 m). Three species were common to both sites, and, in the montane rainforest, three pioneer species and three climax species were investigated. Across species, interspecific variation in photosynthetic capacity was not related to leaf nutrient content. Instead, this variation was related to differences in within-leaf nitrogen allocation, with a tradeoff between investments into compounds related to photosynthetic capacity (higher in pioneer species) versus light-harvesting compounds (higher in climax species). Photosynthetic capacity was significantly lower at the warmer site at 1,700 m altitude. We conclude that (1) within-leaf nutrient allocation is more important than leaf nutrient content per se in controlling interspecific variation in photosynthetic capacity among tree species in tropical Rwanda, and that (2) tropical montane rainforest species exhibit decreased photosynthetic capacity when grown in a warmer environment.
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24. |
- Dusenge, Mirindi Eric, 1986, et al.
(author)
-
Photosynthetic capacity of tropical montane tree species in relation to leaf nutrients, successional strategy and growth temperature
- 2015
-
In: 2015 Canadian Society of Plant Biologist/Eastern Regional meeting; University of Toronto, St George Campus, November 21-22nd, 2015.
-
Conference paper (other academic/artistic)abstract
- Photosynthetic capacity of tree leaves is typically positively related to nutrient content and little affected by changes in growth temperature. These relationships are, however, often poorly supported for tropical trees, for which interspecific differences may be more controlled by within-leaf nutrient allocation than by absolute leaf nutrient content, and little is known regarding photosynthetic acclimation to temperature. To explore the influence of leaf nutrient status, successional strategy and growth temperature on the photosynthetic capacity of tropical trees, we collected data on photosynthetic, chemical and morphological leaf traits of ten tree species in Rwanda. Seven species were studied in a forest plantation at mid-altitude, whereas six species were studied in a cooler montane rainforest at higher altitude. Three species were common to both sites, and, in the montane rainforest, three pioneer species and three climax species were investigated. Across species, interspecific variation in photosynthetic capacity was not related to leaf nutrient content. Instead, this variation was related to differences in within-leaf nitrogen allocation, with a tradeoff between investments into compounds related to photosynthetic capacity (higher in pioneer species) versus light-harvesting compounds (higher in climax species). Photosynthetic capacity was significantly lower at the warmer site. We conclude that (1) within-leaf nutrient allocation is more important than leaf nutrient content per se in controlling interspecific variation in photosynthetic capacity among tree species in tropical Rwanda, and that (2) tropical montane rainforest species exhibit decreased photosynthetic capacity when grown in a warmer environment.
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25. |
- Ellsworth, D. S., et al.
(author)
-
Convergence in phosphorus constraints to photosynthesis in forests around the world
- 2022
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
-
Journal article (peer-reviewed)abstract
- Phosphorus (P) limitation is pervasive in tropical forests. Here the authors analyse the dependence of photosynthesis on leaf N and P in tropical forests, and show that incorporating leaf P constraints in a terrestrial biosphere model enhances its predictive power. Tropical forests take up more carbon (C) from the atmosphere per annum by photosynthesis than any other type of vegetation. Phosphorus (P) limitations to C uptake are paramount for tropical and subtropical forests around the globe. Yet the generality of photosynthesis-P relationships underlying these limitations are in question, and hence are not represented well in terrestrial biosphere models. Here we demonstrate the dependence of photosynthesis and underlying processes on both leaf N and P concentrations. The regulation of photosynthetic capacity by P was similar across four continents. Implementing P constraints in the ORCHIDEE-CNP model, gross photosynthesis was reduced by 36% across the tropics and subtropics relative to traditional N constraints and unlimiting leaf P. Our results provide a quantitative relationship for the P dependence for photosynthesis for the front-end of global terrestrial C models that is consistent with canopy leaf measurements.
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26. |
- Ely, K. S., et al.
(author)
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A reporting format for leaf-level gas exchange data and metadata
- 2021
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In: Ecological Informatics. - : Elsevier BV. - 1574-9541. ; 61
-
Journal article (peer-reviewed)abstract
- Leaf-level gas exchange data support the mechanistic understanding of plant fluxes of carbon and water. These fluxes inform our understanding of ecosystem function, are an important constraint on parameterization of terrestrial biosphere models, are necessary to understand the response of plants to global environmental change, and are integral to efforts to improve crop production. Collection of these data using gas analyzers can be both technically challenging and time consuming, and individual studies generally focus on a small range of species, restricted time periods, or limited geographic regions. The high value of these data is exemplified by the many publications that reuse and synthesize gas exchange data, however the lack of metadata and data reporting conventions make full and efficient use of these data difficult. Here we propose a reporting format for leaf-level gas exchange data and metadata to provide guidance to data contributors on how to store data in repositories to maximize their discoverability, facilitate their efficient reuse, and add value to individual datasets. For data users, the reporting format will better allow data repositories to optimize data search and extraction, and more readily integrate similar data into harmonized synthesis products. The reporting format specifies data table variable naming and unit conventions, as well as metadata characterizing experimental conditions and protocols. For common data types that were the focus of this initial version of the reporting format, i.e., survey measurements, dark respiration, carbon dioxide and light response curves, and parameters derived from those measurements, we took a further step of defining required additional data and metadata that would maximize the potential reuse of those data types. To aid data contributors and the development of data ingest tools by data repositories we provided a translation table comparing the outputs of common gas exchange instruments. Extensive consultation with data collectors, data users, instrument manufacturers, and data scientists was undertaken in order to ensure that the reporting format met community needs. The reporting format presented here is intended to form a foundation for future development that will incorporate additional data types and variables as gas exchange systems and measurement approaches advance in the future. The reporting format is published in the U.S. Department of Energy?s ESS-DIVE data repository, with documentation and future development efforts being maintained in a version control system.
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27. |
- Feng, Zhaozhong, et al.
(author)
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A stomatal ozone flux–response relationship to assess ozone-induced yield loss of winter wheat in subtropical China
- 2012
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 164, s. 16-23
-
Journal article (peer-reviewed)abstract
- Stomatal ozone flux and flux–response relationships were derived for winter wheat (Triticum aestivum L.) grown under fully open-air ozone fumigation. A stomatal conductance (gsto) model developed for wheat in Europe was re-parameterized. Compared to European model parameterizations, the main changes were that the VPD and radiation response functions were made less and more restrictive, respectively, and that the temperature function was omitted. The re-parameterized gsto model performed well with an r2 value of 0.76. The slope and intercept of the regression between observed and predicted gsto were not significantly different from 1 to 0, respectively. An ozone uptake threshold of 12 nmol m−2 s−1 was judged most reasonable for the wheat flux–response relationship in subtropical China. Judging from both flux- and concentration-based relationships, the cultivars investigated seem to be more sensitive to ozone than European cultivars. The new flux–response relationship can be applied to ozone risk assessment in subtropical regions.
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28. |
- Feng, Zhaozhong, et al.
(author)
-
A unifying explanation for variation in ozone sensitivity among woody plants
- 2018
-
In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:1, s. 78-84
-
Journal article (peer-reviewed)abstract
- Tropospheric ozone is considered the most detrimental air pollutant for vegetation at the global scale, with negative consequences for both provisioning and climate regulating ecosystem services. In spite of recent developments in ozone exposure metrics, from a concentration-based to a more physiologically relevant stomatal flux-based index, large-scale ozone risk assessment is still complicated by a large and unexplained variation in ozone sensitivity among tree species. Here, we explored whether the variation in ozone sensitivity among woody species can be linked to interspecific variation in leaf morphology. We found that ozone tolerance at the leaf level was closely linked to leaf dry mass per unit leaf area (LMA) and that whole-tree biomass reductions were more strongly related to stomatal flux per unit leaf mass (r 2 =0.56) than to stomatal flux per unit leaf area (r 2 =0.42). Furthermore, the interspecific variation in slopes of ozone flux–response relationships was considerably lower when expressed on a leaf mass basis (coefficient of variation, CV=36%) than when expressed on a leaf area basis (CV=66%), and relationships for broadleaf and needle-leaf species converged when using the mass-based index. These results show that much of the variation in ozone sensitivity among woody plants can be explained by interspecific variation in LMA and that large-scale ozone impact assessment could be greatly improved by considering this well-known and easily measured leaf trait.
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29. |
- Feng, Zhaozhong, et al.
(author)
-
Constraints to nitrogen acquisition of terrestrial plants under elevated CO2
- 2015
-
In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 21:8, s. 3152-3168
-
Journal article (peer-reviewed)abstract
- A key part of the uncertainty in terrestrial feedbacks on climate change is related to how and to what extent nitrogen (N) availability constrains the stimulation of terrestrial productivity by elevated CO2 (eCO2), and whether or not this constraint will become stronger over time. We explored the ecosystem-scale relationship between responses of plant productivity and N acquisition to eCO2 in Free-Air CO2 Enrichment (FACE) experiments in grassland, cropland and forest ecosystems and found that: (i) In all three ecosystem types, this relationship was positive, linear, and strong (r2 = 0.68), but exhibited a negative intercept such that plant N acquisition was decreased by 10% when eCO2 caused neutral or modest changes in productivity. Since the ecosystems were markedly N limited, plants with minimal productivity responses to eCO2 likely acquired less N than ambient CO2-grown counterparts because access was decreased, and not because demand was lower. (ii) Plant N concentration was lower under eCO2, and this decrease was independent of the presence or magnitude of eCO2-induced productivity enhancement, refuting the long-held hypothesis that this effect results from growth dilution. (iii) Effects of eCO2 on productivity and N acquisition did not diminish over time, while the typical eCO2-induced decrease in plant N concentration did. Our results suggest that, at the decennial time scale covered by FACE studies, N limitation of eCO2-induced terrestrial productivity enhancement is associated with negative effects of eCO2 on plant N acquisition rather than with growth dilution of plant N or processes leading to progressive N limitation.
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30. |
- Feng, Z. Z., et al.
(author)
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Comparison of crop yield sensitivity to ozone between open-top chamber and free-air experiments
- 2018
-
In: Global Change Biology. - : Wiley. - 1354-1013. ; 24:6, s. 2231-2238
-
Journal article (peer-reviewed)abstract
- Assessments of the impacts of ozone (O-3) on regional and global food production are currently based on results from experiments using open-top chambers (OTCs). However, there are concerns that these impact estimates might be biased due to the environmental artifacts imposed by this enclosure system. In this study, we collated O-3 exposure and yield data for three major crop species-wheat, rice, and soybean-for which O-3 experiments have been conducted with OTCs as well as the ecologically more realistic free-air O-3 elevation (O-3-FACE) exposure system; both within the same cultivation region and country. For all three crops, we found that the sensitivity of crop yield to the O-3 metric AOT40 (accumulated hourly O-3 exposure above a cut-off threshold concentration of 40 ppb) significantly differed between OTC and O-3-FACE experiments. In wheat and rice, O-3 sensitivity was higher in O-3-FACE than OTC experiments, while the opposite was the case for soybean. In all three crops, these differences could be linked to factors influencing stomatal conductance (manipulation of water inputs, passive chamber warming, and cultivar differences in gas exchange). Our study thus highlights the importance of accounting for factors that control stomatal O-3 flux when applying experimental data to assess O-3 impacts on crops at large spatial scales.
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31. |
- Franz, M., et al.
(author)
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Evaluation of simulated ozone effects in forest ecosystems against biomass damage estimates from fumigation experiments
- 2018
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 15:22, s. 6941-6957
-
Journal article (peer-reviewed)abstract
- Regional estimates of the effects of ozone pollution on forest growth depend on the availability of reliable injury functions that estimate a representative ecosystem response to ozone exposure. A number of such injury functions for forest tree species and forest functional types have recently been published and subsequently applied in terrestrial biosphere models to estimate regional or global effects of ozone on forest tree productivity and carbon storage in the living plant biomass. The resulting impacts estimated by these biosphere models show large uncertainty in the magnitude of ozone effects predicted. To understand the role that these injury functions play in determining the variability in estimated ozone impacts, we use the O-CN biosphere model to provide a standardised modelling framework. We test four published injury functions describing the leaf-level, photosynthetic response to ozone exposure (targeting the maximum carboxylation capacity of Rubisco (V-cmax) or net pho-tosynthesis) in terms of their simulated whole-tree biomass responses against data from 23 ozone filtration/fumigation experiments conducted with young trees from European tree species at sites across Europe with a range of climatic conditions. Our results show that none of these previously published injury functions lead to simulated whole-tree biomass reductions in agreement with the observed dose-response relationships derived from these field experiments and instead lead to significant over-or underestimations of the ozone effect. By re-parameterising these photosynthetically based injury functions, we develop linear, plant-functional-typespecific dose-response relationships, which provide accurate simulations of the observed whole-tree biomass response across these 23 experiments.
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32. |
- Gardner, A., et al.
(author)
-
Optimal stomatal theory predicts CO2 responses of stomatal conductance in both gymnosperm and angiosperm trees
- 2022
-
In: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 237:4, s. 1229-41
-
Journal article (peer-reviewed)abstract
- Optimal stomatal theory predicts that stomata operate to maximise photosynthesis (A(net)) and minimise transpirational water loss to achieve optimal intrinsic water-use efficiency (iWUE). We tested whether this theory can predict stomatal responses to elevated atmospheric CO2 (eCO(2)), and whether it can capture differences in responsiveness among woody plant functional types (PFTs). We conducted a meta-analysis of tree studies of the effect of eCO(2) on iWUE and its components A(net) and stomatal conductance (g(s)). We compared three PFTs, using the unified stomatal optimisation (USO) model to account for confounding effects of leaf-air vapour pressure difference (D). We expected smaller g(s), but greater A(net), responses to eCO(2) in gymnosperms compared with angiosperm PFTs. We found that iWUE increased in proportion to increasing eCO(2) in all PFTs, and that increases in A(net) had stronger effects than reductions in g(s). The USO model correctly captured stomatal behaviour with eCO(2) across most datasets. The chief difference among PFTs was a lower stomatal slope parameter (g(1)) for the gymnosperm, compared with angiosperm, species. Land surface models can use the USO model to describe stomatal behaviour under changing atmospheric CO2 conditions.
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33. |
- Hasper, Thomas Berg, et al.
(author)
-
Stomatal CO2 responsiveness and photosynthetic capacity of tropical woody species in relation to taxonomy and functional traits
- 2017
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In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 184:1, s. 43-57
-
Journal article (peer-reviewed)abstract
- © 2017 The Author(s)Stomatal CO2 responsiveness and photosynthetic capacity vary greatly among plant species, but the factors controlling these physiological leaf traits are often poorly understood. To explore if these traits are linked to taxonomic group identity and/or to other plant functional traits, we investigated the short-term stomatal CO2 responses and the maximum rates of photosynthetic carboxylation (Vcmax) and electron transport (Jmax) in an evolutionary broad range of tropical woody plant species. The study included 21 species representing four major seed plant taxa: gymnosperms, monocots, rosids and asterids. We found that stomatal closure responses to increased CO2 were stronger in angiosperms than in gymnosperms, and in monocots compared to dicots. Stomatal CO2 responsiveness was not significantly related to any of the other functional traits investigated, while a parameter describing the relationship between photosynthesis and stomatal conductance in combined leaf gas exchange models (g1) was related to leaf area-specific plant hydraulic conductance. For photosynthesis, we found that the interspecific variation in Vcmax and Jmax was related to within leaf nitrogen (N) allocation rather than to area-based total leaf N content. Within-leaf N allocation and water use were strongly co-ordinated (r2 = 0.67), such that species with high fractional N investments into compounds maximizing photosynthetic capacity also had high stomatal conductance. We conclude that while stomatal CO2 responsiveness of tropical woody species seems poorly related to other plant functional traits, photosynthetic capacity is linked to fractional within-leaf N allocation rather than total leaf N content and is closely co-ordinated with leaf water use.
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34. |
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35. |
- Hasper, Thomas Berg, et al.
(author)
-
Water use by Swedish boreal forests in a changing climate
- 2016
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In: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 30:5, s. 690-699
-
Journal article (peer-reviewed)abstract
- The rising levels of atmospheric carbon dioxide concentration ([CO2]) and temperature have the potential to substantially affect the terrestrial water and energy balance by altering the stomatal conductance and transpiration of trees. Many models assume decreases in stomatal conductance and plant water use under rising [CO2], which has been used as a plausible explanation for the positive global trend in river run-off over the past century. Plant water use is, however, also affected by changes in temperature, precipitation and land use, and there is yet no consensus about the contribution of different drivers to temporal trends of evapotranspiration (ET) and river run-off. In this study, we assessed water-use responses to climate change by using both long-term monitoring and experimental data in Swedish boreal forests. Historical trends and patterns in ET of large-scale boreal landscapes were determined using climate and run-off data from the past 50 years, while explicit tree water-use responses to elevated [CO2] and/or air temperature were examined in a whole-tree chamber experiment using mature Norway spruce (Picea abies (L.) Karst.) trees. The results demonstrated that ET estimated from water budgets at the catchment scale increased by 18% over the past 50 years while run-off did not significantly change. The increase in ET was related to increasing precipitation and a steady increase in forest standing biomass over time. The whole-tree chamber experiment showed that Norway spruce trees did not save water under elevated [CO2] and that experimentally elevated air temperature did not increase transpiration as decreased stomatal conductance cancelled the effect of higher vapour pressure deficit in warmed air. Our findings have important implications for projections of future water use of European boreal coniferous forests, indicating that changes in precipitation and standing biomass are more important than the effects of elevated [CO2] or temperature on transpiration rates.
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36. |
- Hasper, Thomas, et al.
(author)
-
Stomatal responses of Eucalyptus (Eucalyptus sp.) grown at different concentration of carbon dioxide (CO2) and temperature, Western Sydney, Australia
- 2012
-
In: SEB Annual Main Meeting 2012, Salzburg 29 June - 2 July 2012.
-
Conference paper (other academic/artistic)abstract
- Conclusions •Even with leaves in all treatments exhibited stomatal closure responses to increased [CO2], this response was significantly reduced in leaves growing in Ce treatments, showing that stomata of E. globulus do acclimate to growth in [CO2]. • The stomatal CO2 response of plants grown in Te did not differ from that in plants grown in Ta. • Te and/or Ce treatments did not have any effect on stomatal density/size or KL. • This study indicates that while stomatal CO2 responses has the potential to cause water savings under Ce, this potential is reduced by stomatal acclimation to prevailing growth [CO2] and is likely not present during conditions when gs is constrained by plant hydraulics.
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37. |
- Hogg, A., et al.
(author)
-
Multi-year measurements of stomatal and non-stomatal fluxes
- 2007
-
In: American Geophysical Union, Meeting in San Francisco, 10–14 December 2007.
-
Conference paper (other academic/artistic)abstract
- Measurements of ozone, sensible heat, and latent heat fluxes, as well as relative humidity, temperature, pressure, wind speed, leaf area index, ambient ozone, and plant physiological parameters were made at a northern mixed hardwood forest located at the University of Michigan Biological Station (UMBS) in northern Michigan during the growing seasons 2002 through 2005. The ozone measurements were used to calculate total ozone flux and partitioning between stomatal and non-stomatal sinks. Total ozone flux varied diurnally with downward flux reaching -100 μmol m-2 h-1 at midday, at or near zero at night. Mean daytime canopy conductance varied over the four years: 0.39 mol m-2 s-1 (2002), 0.41 mol m-2 s-1 (2003), 0.52 mol m-2 s-1 (2004), and 0.43 mol m-2 s-1 (2005). Stomatal conductance showed expected patterns of behavior with respect to photosynthetic photon flux density (PPFD) and vapor pressure deficit (VPD). Estimated peak growing season stomatal ozone burden (flux) was 2.9 x105 nmol m-2 in 2002, 5.6 x105 nmol m-2 in 2003, 6.6 x105 nmol m-2 in 2004, and 4.1 x105 nmol m-2 in 2005. Non-stomatal conductance for ozone increased monotonically with increasing PPFD, and increased with temperature before falling off again at high temperature. Daytime non-stomatal ozone sinks were large and varied with time and environmental drivers. Daytime non-stomatal ozone conductance accounted for as much as 61% (2002), 31% (2003), 36% (2004), or 57% (2005) of canopy conductance, with the non-stomatal partition representing 4.2x105 nmol m-2 (2002), 2.0x105 nmol m-2 (2003), 3.5x105 nmol m-2 (2004), 3.5x105 nmol m-2 (2005) of the flux. Non-stomatal ozone conductance was strongly diurnal and a significant proportion of total canopy conductance.
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38. |
- Hogg, A., et al.
(author)
-
Stomatal and non-stomatal fluxes of ozone to a northern mixed hardwood forest
- 2007
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In: Tellus Series B-Chemical and Physical Meteorology. - 0280-6509. ; 59:3, s. 514-525
-
Journal article (peer-reviewed)abstract
- Measurements of ozone, sensible heat, and latent heat fluxes and plant physiological parameters were made at a northern mixed hardwood forest located at the University of Michigan Biological Station in northern Michigan from June 27 to September 28, 2002. These measurements were used to calculate total ozone flux and partitioning between stomatal and non-stomatal sinks. Total ozone flux varied diurnally with maximum values reaching 100 mu mol m(-2) h(-1) at midday and minimums at or near zero at night. Mean daytime canopy conductance was 0.5 mol m(-2) s(-1). During daytime, non-stomatal ozone conductance accounted for as much as 66% of canopy conductance, with the non-stomatal sink representing 63% of the ozone flux. Stomatal conductance showed expected patterns of behaviour with respect to photosynthetic photon flux density (PPFD) and vapour pressure defecit (VPD). Non-stomatal conductance for ozone increased monotonically with increasing PPFD, increased with temperature (T) before falling off again at high T, and behaved similarly for VPD. Day-time non-stomatal ozone sinks are large and vary with time and environmental drivers, particularly PPFD and T. This information is crucial to deriving mechanistic models that can simulate ozone uptake by different vegetation types.
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39. |
- Jaramillo, Fernando, et al.
(author)
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Dominant effect of increasing forest biomass on evapotranspiration: Interpretations of movement in Budyko space
- 2018
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In: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 22, s. 567-580
-
Journal article (peer-reviewed)abstract
- During the last 6 decades, forest biomass has increased in Sweden mainly due to forest management, with a possible increasing effect on evapotranspiration. However, increasing global CO 2 concentrations may also trigger physiological water-saving responses in broadleaf tree species, and to a lesser degree in some needleleaf conifer species, inducing an opposite effect. Additionally, changes in other forest attributes may also affect evapotranspiration. In this study, we aimed to detect the dominating effect(s) of forest change on evapotranspiration by studying changes in the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio, during the period 1961-2012. We first used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 temperate and boreal basins during this period. We found that movements in Budyko space could not be explained by climatic changes in precipitation and potential evapotranspiration in 60% of these basins, suggesting the existence of other dominant drivers of hydroclimatic change. In both the temperate and boreal basin groups studied, a negative climatic effect on the evaporative ratio was counteracted by a positive residual effect. The positive residual effect occurred along with increasing standing forest biomass in the temperate and boreal basin groups, increasing forest cover in the temperate basin group and no apparent changes in forest species composition in any group. From the three forest attributes, standing forest biomass was the one that could explain most of the variance of the residual effect in both basin groups. These results further suggest that the water-saving response to increasing CO 2 in these forests is either negligible or overridden by the opposite effect of the increasing forest biomass. Thus, we conclude that increasing standing forest biomass is the dominant driver of long-term and large-scale evapotranspiration changes in Swedish forests.
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40. |
- Johansson, Karin S L, et al.
(author)
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Genetic controls of short- and long-term stomatal CO2 responses in Arabidopsis thaliana
- 2020
-
In: Annals of botany. - : Oxford University Press (OUP). - 1095-8290 .- 0305-7364. ; 126:1, s. 179-190
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Journal article (peer-reviewed)abstract
- © The Author(s) 2020. Published by Oxford University Press on behalf of the Annals of Botany Company. BACKGROUND AND AIMS: The stomatal conductance (gs) of most plant species decreases in response to elevated atmospheric CO2 concentration. This response could have a significant impact on plant water use in a future climate. However, the regulation of the CO2-induced stomatal closure response is not fully understood. Moreover, the potential genetic links between short-term (within minutes to hours) and long-term (within weeks to months) responses of gs to increased atmospheric CO2 have not been explored. METHODS: We used Arabidopsis thaliana recombinant inbred lines originating from accessions Col-0 (strong CO2 response) and C24 (weak CO2 response) to study short- and long-term controls of gs. Quantitative trait locus (QTL) mapping was used to identify loci controlling short- and long-term gs responses to elevated CO2, as well as other stomata-related traits. KEY RESULTS: Short- and long-term stomatal responses to elevated CO2 were significantly correlated. Both short- and long-term responses were associated with a QTL at the end of chromosome 2. The location of this QTL was confirmed using near-isogenic lines and it was fine-mapped to a 410-kb region. The QTL did not correspond to any known gene involved in stomatal closure and had no effect on the responsiveness to abscisic acid. Additionally, we identified numerous other loci associated with stomatal regulation. CONCLUSIONS: We identified and confirmed the effect of a strong QTL corresponding to a yet unknown regulator of stomatal closure in response to elevated CO2 concentration. The correlation between short- and long-term stomatal CO2 responses and the genetic link between these traits highlight the importance of understanding guard cell CO2 signalling to predict and manipulate plant water use in a world with increasing atmospheric CO2 concentration. This study demonstrates the power of using natural variation to unravel the genetic regulation of complex traits.
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41. |
- Johansson, Karin S L, et al.
(author)
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Molecular basis of variation in stomatal responsiveness to elevated CO2
- 2015
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In: Agriculture and Climate Change - Adapting Crops to Increased Uncertainty. 15-17 February 2015, Amsterdam, the Netherlands. Procedia Environmental Sciences. - : Elsevier. - 1878-0296.
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Conference paper (other academic/artistic)abstract
- Stomata are small pores in the surface of plant leaves, balancing the uptake of CO2 against the loss of water vapour. As drought stress is projected to increase in many parts of the world, an improved understanding of how plants regulate their stomata in response to environmental stimuli may have important implications for securing food production in a future climate. The stomata of most plants respond to elevated CO2 concentration by partial closing, but the magnitude of this response shows a large variation among species and ecotypes. Plants that substantially decrease stomatal conductance under elevated CO2 reduce their water consumption and increase their water-use efficiency. However, the genetic basis for inter- and intraspecific variation in responsiveness is poorly understood, as are the mechanisms for sensing and responding to CO2. In the current study, we have measured the short-term stomatal response to elevated CO2 in a population of Arabidopsis thaliana recombinant inbred lines (RILs) originating from a cross between two parental genotypes showing a large difference in stomatal responsiveness. Hence, this RIL population showed a broad range in stomatal responsiveness, ranging from a 10% to a 60% reduction of stomatal conductance following an increase in CO2 concentration from 400 to 800 ppm. Using quantitative trait locus (QTL) mapping we have identified two genetic loci involved in the stomatal response to elevated CO2. Potential candidate genes regulating the stomatal response will be discussed.
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42. |
- Karlsson, Per Erik, 1957, et al.
(author)
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Evidence for Impacts of Near-ambient Ozone Concentrations on Vegetation in Southern Sweden
- 2009
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In: Ambio. - : Royal Swedish Academy of Sciences. ; 38:8, s. 425-431
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Journal article (peer-reviewed)abstract
- Substantial impacts of near-ambient ozone concentrations on agricultural crops, trees, and seminatural vegetation are demonstrated for southern Sweden. Impacts of ambient ozone levels (2–15 μL L-¹ hr annual accumulated ozone exposure over a threshold of 40 nL L-¹ [AOT40]) range from a 2%–10% reduction for trees (e.g., leaf chlorophyll, tree growth) up to a 15% reduction for crops (e.g., yield, wheat/potato). Visible leaf injury on bioindicator plants caused by ambient ozone levels has been clearly demonstrated. The humid climatic conditions in Sweden promote high rates of leaf ozone uptake at a certain ozone concentration. This likely explains the comparatively large ozone impacts found for vegetation in southern Sweden at relatively low ozone concentrations in the air. It is important that the future methods used for the representation of ozone impacts on vegetation across Europe are based on the leaf ozone uptake concept and not on concentration-based exposure indices, such as AOT40.
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43. |
- Karlsson, Per Erik, 1957, et al.
(author)
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Impact of ozone on the growth of birch (Betula pendula) saplings
- 2003
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In: Environmental Pollution. - 0269-7491. ; 124:3, s. 485-495
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Journal article (peer-reviewed)abstract
- Saplings of one half-sib family of birch, Betula pendula, were exposed to three levels of ozone in open-top chambers (OTCs) during two growing seasons 1997-1998. The ozone treatments were non-filtered air (NF, accumulated daylight AOT40 over the two growing seasons of 3.0 mul l(-1) h), non-filtered air with extra ozone (NF +, accumulated daylight AOT40 of 27.3 mul l(-1) h) and nonfiltered air with additional extra ozone (NF++, accumulated daylight AOT40 of 120 mul l(-1) h), The birch saplings, including the roots, were harvested after the first and second growing seasons. After the first growing season, the NF++ treatment reduced the total wood biomass by 22%, relative to the NF treatment. There was no further reduction of the total wood biomass in the NF++ treatment after the second growing season. The root biomass was reduced by 30% after the first growing season. The shoot/root ratio, as well as the proportional biomass of leaves, were increased by ozone during both years. The ozone impact on the relative growth rate was estimated to -2% per 10 mul l(-1) h daylight AOT40 per growing season. (C) 2003 Elsevier Science Ltd. All rights reserved.
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44. |
- Karlsson, Per Erik, 1957, et al.
(author)
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Negative impact of ozone on the stem basal area increment of mature Norway spruce in south Sweden
- 2006
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In: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 232:1-3, s. 146-151
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Journal article (peer-reviewed)abstract
- The relative annual basal area increment of mature Norway spruce trees in south-central Sweden during 9 years was used as the response variable and analysed in relation to ozone exposure, meteorological conditions, soil moisture and stand characteristics. The method used was a modified multiple regression analysis, allowing for dependencies between observations from the same plots. The selected statistical model explained 91% of the variation in the annual relative basal area increment. The strongest explanatory variable was the stand basal area, followed by the temperature sum and the soil moisture index. After these three variables, the ozone index was the most important variable. Its effect was negative and highly significant. The average daylight ozone concentration gave a slightly better model fit as compared to the accumulated exposure during daylight hours above a threshold of 40 nmol mol−1 (AOT40). The predicted effect of ozone within the range of annual ozone exposures found in this study (18008700 nmol mol−1 h AOT40), was in absolute values a 0.8% decrease in the relative annual basal area increment. This could be compared with the mean relative annual increment measured during the study period of 4.6%. Our results provide statistical evidence that ground level ozone can have a negative impact on the stem growth of mature Norway spruce trees under field conditions.
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45. |
- Karlsson, Per Erik, 1957, et al.
(author)
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New critical levels for ozone effects on young trees based on AOT40 and simulated cumulative leaf uptake of ozone
- 2004
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In: Atmospheric Environment. - : Elsevier BV. - 1352-2310. ; 38:15, s. 2283-2294
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Journal article (peer-reviewed)abstract
- Leaf or needle ozone uptake was estimated for young trees at seven experimental sites across Europe using a stomatal conductance simulation model. Dose-response relationships based on cumulative leaf uptake of ozone (CUO) were calculated using different hourly ozone flux thresholds and these were compared to dose-response relationships based on daylight AOT40, which is currently used within the UNECE Convention on Long-Range Transboundary Air Pollution (CLRTAP). Regression analysis showed that the CUO-biomass response relationships were highly significant for both coniferous and broadleaf trees, and independent of which ozone flux threshold was applied. On the basis of this regressions analysis, an hourly flux threshold of 1.6 nmol m(-2) s(-1) (COO > 1.6) is proposed as the most appropriate for all species categories in deriving dose-response relationships. The analysis indicated that the current critical level for ozone impacts on European forests of AOT40 10 ppm h may not protect the most sensitive receptors and that critical levels for AOT40 and CUO > 1.6 of 5 ppm h and 4 mmol m(-2), respectively, are more appropriate. The research identified weaker dose-response relationships for the CUO exposure index compared with AOT40. Distinguishing between sensitive and less sensitive species substantially improved the CUO-biomass response relationships although, still, to a lesser extent than when exposure was expressed as AOT40. (C) 2004 Elsevier Ltd. All rights reserved.
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46. |
- Karlsson, Per Erik, 1957, et al.
(author)
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Risk assessments for forest trees: The performance of the ozone flux versus the AOT concepts
- 2007
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In: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 146:3, s. 608-616
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Journal article (peer-reviewed)abstract
- Published ozone exposure-response relationships from experimental studies with young trees performed at different sites across Europe were re-analysed in order to test the performance of ozone exposure indices based on AOTX (Accumulated exposure Over a Threshold of X nmol mol(-1)) and AF(st)Y (Accumulated Stomatal Flux above a threshold of Y nmol m(-2) s(-1)). AF(st)1.6 was superior, as compared to AOT40, for explaining biomass reductions, when ozone sensitive species with differing leaf morphology were included in the analysis, while this was not the case for less sensitive species. A re-analysis of data with young black cherry trees, subject to different irrigation regimes, indicated that leaf visible injuries were more strongly related to the estimated stomatal ozone uptake, as compared to the ozone concentration in the air. Experimental data with different clones of silver birch indicated that leaf thickness was also an important factor influencing the development of ozone induced leaf visible injury. (c) 2006 Elsevier Ltd. All rights reserved.
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47. |
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48. |
- Klingberg, Jenny, 1978, et al.
(author)
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Ozone risk for vegetation in the future climate of Europe based on stomatal ozone uptake calculations
- 2011
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In: Tellus A. - : Stockholm University Press. ; 63, s. 174-187
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Journal article (peer-reviewed)abstract
- The negative impacts of surface ozone (O3) on vegetation are determined by external exposure, leaf gas exchange and plant antioxidant defence capacity, all dependent on climate and CO2 concentrations. In this study the influence of climate change on simulated stomatal O3 uptake of a generic crop and a generic deciduous tree at ten European sites was investigated, using the LRTAP Mapping Manual stomatal flux model. O3 concentrations are calculated by a chemistry transport model (MATCH) for three 30-year time-windows (1961-1990, 2021-2050, 2071-2100), with constant precursor emissions and meteorology from a regional climate model (RCA3). Despite substantially increased modelled future O3 concentrations in central and southern Europe, the flux-based risk for O3 damage to vegetation is predicted to remain unchanged or decrease at most sites, mainly as a result of projected reductions in stomatal conductance under rising CO2 concentrations. Drier conditions in southern Europe are also important for this result. At northern latitudes, the current parameterisation of the stomatal conductance model suggest O3 uptake to be mainly limited by temperature. This study demonstrates the importance of accounting for the influences by climate and CO2 on stomatal O3 uptake, and of developing their representation in models, for risk assessment involving climate change.
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49. |
- Konarska, Janina, 1986, et al.
(author)
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319: Tree Health, Growth and Cooling Effects at Contrasting Urban Sites in Gothenburg, Sweden
- 2018
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In: 10th International Conference on Urban Climate/14th Symposium on the Urban Environment, New York, US, August 2018.
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Conference paper (other academic/artistic)abstract
- One of the most important ecosystem services provided by urban trees is the mitigation of urban heat. However, this cooling effect may be compromised due to vulnerability of urban trees to harsh urban environment and ongoing climate change. In this project we aim to analyse the growth and health of urban tree species in Gothenburg, Sweden in response to different urban growing conditions, as well as the impact of heat and drought stress on tree cooling benefits through changes to shading effect and transpiration. Three species with different adaptation mechanisms to drought stress were selected: Aesculus hippocastanum, Tilia europaea and Quercus palustris. For each species, trees of the same age planted at adjacent paved and unpaved sites were chosen for the study. In 2017, measured traits included stomatal conductance and transpiration rates, pre-dawn and midday water potentials, chlorophyll content, and leaf area density. In 2018, additional microclimate and human thermal comfort measurements were added to assess the cooling benefits provided by trees. The summertime measurements in 2017 showed significant differences in multiple plant traits between contrasting sites for all species studied, with trees at paved sites showing reduced gas exchange, chlorophyll content and leaf area density compared to sites with a higher fraction of permeable surfaces. These differences were observed both on a hot summer day following a dry period, as well as on a cooler day following a wet period. A clear difference in water use dynamics between species with ”tolerant” (e.g. Q. palustris) and ”avoiding” (e.g. A. hippocastanum) mechanisms against drought stress were also observed. The results highlight the importance of proper planning and species selection in supporting the health and resilience of the urban forest as well as maximising its cooling benefits. The study will be continued in Melbourne, Australia with the focus on urban tree performance alongside water sensitive urban design (WSUD).
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50. |
- Konarska, Janina, 1986, et al.
(author)
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Surface paving more important than species in determining the physiology, growth and cooling effects of urban trees
- 2023
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In: Landscape and Urban Planning. - 0169-2046. ; 240
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Journal article (peer-reviewed)abstract
- Urban trees provide numerous ecosystem services including the mitigation of urban heat. However, this cooling effect is often restricted due to poor tree growth and health caused by harsh growing conditions. The aim of this study is to analyse the influence of surface paving on the physiology, growth and cooling benefits of street trees of three common species with contrasting drought tolerance (Aesculus hippocastanum, Tilia × europaea and Quercus palustris) in Gothenburg, Sweden. Tree structural parameters, leaf water potentials, gas exchange, leaf area density and chlorophyll content were measured in three summertime periods in 2017 and 2018. Moreover, based on the measured data, the cooling effects of studied trees due to shading and transpiration were modelled. For all species, trees at highly paved sites were found to have significantly reduced growth, physiological performance and cooling effects compared to sites with a higher degree of permeable surfaces. This negative effect of surface paving was stronger than the effect of species, despite differences in drought tolerance and water use strategy between studied species. Based on the sensitivity of species to surface paving, we recommend Q. palustris and T. europaea for sites with good growing conditions due to their potential to maintain high water use and growth rates, and A. hippocastanum for highly paved sites where shading is not the primary ecosystem service sought. Our findings emphasise the importance of tree planting design in supporting urban tree growth and the continuous provision of ecosystem services, particularly in the context of the changing climate.
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