| 1. |
- Adolfsson, Lisa, 1984, et al.
(författare)
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Mycorrhiza Symbiosis Increases the Surface for Sunlight Capture in Medicago truncatula for Better Photosynthetic Production
- 2015
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 10:1
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Tidskriftsartikel (refereegranskat)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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| 2. |
- af Ekenstam, Angelica, et al.
(författare)
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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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Ingår i: EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 3. |
- Aloysie, Manishimwe, et al.
(författare)
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Warming Responses of Leaf Morphology Are Highly Variable among Tropical Tree Species
- 2022
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 13:2
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Barth, Sabine, 1974, et al.
(författare)
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Water-Use-Efficiency of Forests Exposed to Elevated Carbon Dioxide and/or Elevated Tropospheric Ozone
- 2009
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Ingår i: 8th International Carbon Dioxide Conference, Jena Germany, 13-19 September 2009.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 5. |
- Broberg, Malin, 1989, et al.
(författare)
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Effects of ozone, drought and heat stress on wheat yield and grain quality
- 2023
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Ingår i: Agriculture, Ecosystems & Environment. - 0167-8809. ; 352:15
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Broberg, Malin, 1989, et al.
(författare)
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Fertilizer efficiency in wheat is reduced by ozone pollution
- 2017
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 607-608, s. 876-880
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Buker, P, et al.
(författare)
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Comparison of different stomatal conductance algorithms for ozone flux modelling
- 2005
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Ingår i: UNECE – Workshop “Critical Levels of Ozone: Further applying and developing the flux-based concept”, Obergurgl, 15-19 November 2005.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 8. |
- Buker, P., et al.
(författare)
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DO3SE modelling of soil moisture to determine ozone flux to forest trees
- 2012
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:12, s. 5537-5562
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Büker, P, et al.
(författare)
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New flux based doseeresponse relationships for ozone for European forest tree species
- 2015
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 206, s. 163-174
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Carroll, M. A., et al.
(författare)
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Reactive nitrogen oxide fluxes to a mixed hardwood forest
- 2008
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Ingår i: International Geosphere-Biosphere Programme, Congress in May 2008.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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