| 1. |
- Kehoe, Laura, et al.
(author)
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Make EU trade with Brazil sustainable
- 2019
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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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| 2. |
- Konarska, Janina, 1986, et al.
(author)
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Transpiration of urban trees and its cooling effect in a high latitude city
- 2016
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In: International journal of biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 60:1, s. 159-172
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Journal article (peer-reviewed)abstract
- An important ecosystem service provided by urban trees is the cooling effect caused by their transpiration. The aim of this study was to quantify the magnitude of daytime and night-time transpiration of common urban tree species in a high latitude city (Gothenburg, Sweden), to analyse the influence of weather conditions and surface permeability on the tree transpiration, and to find out whether tree transpiration contributed to daytime or nocturnal cooling. Stomatal conductance and leaf transpiration at day and night were measured on mature street and park trees of seven common tree species in Gothenburg: Tilia europaea, Quercus robur, Betula pendula, Acer platanoides, Aesculus hippocastanum, Fagus sylvatica and Prunus serrulata. Transpiration increased with vapour pressure deficit and photosynthetically active radiation. Midday rates of sunlit leaves ranged from less than 1 mmol m−2 s−1 (B. pendula) to over 3 mmol m−2 s−1 (Q. robur). Daytime stomatal conductance was positively related to the fraction of permeable surfaces within the vertically projected crown area. A simple estimate of available rainwater, comprising of precipitation sum and fractional surface permeability within the crown area, was found to explain 68 % of variation in midday stomatal conductance. Night-time transpiration was observed in all studied species and amounted to 7 and 20 % of midday transpiration of sunlit and shaded leaves, respectively. With an estimated night-time latent heat flux of 24 W m−2, tree transpiration significantly increased the cooling rate around and shortly after sunset, but not later in the night. Despite a strong midday latent heat flux of 206 W m−2, a cooling effect of tree transpiration was not observed during the day.
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| 3. |
- Konarska, Janina, 1986, et al.
(author)
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Transpiration of urban trees and its impact on nocturnal cooling in Gothenburg, Sweden
- 2015
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In: ICUC9 – 9 th International Conference on Urban Climate jointly with 12th Symposium on the Urban Environment. 20-24 July 2015, Toulouse, France.
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Conference paper (other academic/artistic)abstract
- One of the ecosystem services provided by urban trees is the cooling effect caused by their transpiration. However, while the transpiration of forest trees has been widely studied, little research has been conducted on the daytime and night-time transpirational cooling effect of mature urban trees. Knowledge about the transpiration of street and park trees and its response to different environmental factors can prove useful in estimating the thermal influence of urban greenery as well as in urban planning and management. The aim of this study is to i) quantify the magnitude and diurnal variation of transpiration of common urban tree species in a high latitude city (Gothenburg, Sweden), ii) analyse the influence of weather conditions and fraction of permeable surfaces within the vertically projected crown area on tree transpiration, and iii) find out whether transpiration of urban trees remains active during the night and therefore contributes to nocturnal cooling. Measurements were conducted on mature street and park trees of seven tree species common in Gothenburg: Tilia europaea (Common lime), Quercus robur (English oak), Betula pendula (Silver birch), Acer platanoides (Norway maple), Aesculus hippocastanum (Horse chestnut), Fagus sylvatica (European beech) and Prunus serrulata (Japanese cherry). Stomatal conductance and leaf transpiration were measured using a LI-6400XT Portable Photosynthesis System (LI-COR Biosciences) at daytime and night-time on warm summer days of 2012-2013 in Gothenburg. Leaf area index (LAI) of the studied trees was measured with a LAI-2200 Plant Canopy Analyser (LI-COR Biosciences) in order to estimate the latent heat flux due to tree transpiration. Leaf transpiration was found to increase with vapour pressure deficit and photosynthetically active radiation, with on average 22% of the midday incoming solar radiation being converted into latent heat flux. Midday rates of sunlit leaves varied between species, ranging from less than 1 mmol m-2 s-1 (B. pendula) to over 3 mmol m-2 s-1 (Q. robur). Daytime stomatal conductance was positively related to the fraction of permeable surfaces within the vertically projected tree crown area. A simple estimate of available rainwater, comprising of precipitation sum and a fractional surface permeability within the tree crown area, was found to explain 68% of variation in midday stomatal conductance. The results indicate that a high fractional surface permeability can minimize the frequency of water stress experienced by urban trees and enhance their transpirational cooling. Night-time transpiration was observed in all studied species and was positively related to daytime tree water use. Nocturnal transpiration amounted to 7% and 20% of midday transpiration of sunlit and shaded leaves, respectively. With an estimated latent heat flux of 27 W m-2, evening tree transpiration enhanced the cooling rates around and 1-2 hours after sunset, but not later in the night. The results of transpiration measurements will be combined with vegetation data derived from LIDAR and LAI measurements to estimate neighbourhood- to city-scale cooling effect provided by urban trees.
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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
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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.
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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. |
- Aloysie, Manishimwe, et al.
(author)
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Warming Responses of Leaf Morphology Are Highly Variable among Tropical Tree Species
- 2022
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In: Forests. - : MDPI AG. - 1999-4907. ; 13:2
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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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| 7. |
- 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
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In: 8th International Carbon Dioxide Conference, Jena Germany, 13-19 September 2009.
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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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| 8. |
- Broberg, Malin, 1989, et al.
(author)
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Effects of ozone, drought and heat stress on wheat yield and grain quality
- 2023
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In: Agriculture, Ecosystems & Environment. - 0167-8809. ; 352:15
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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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| 9. |
- Broberg, Malin, 1989, et al.
(author)
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Fertilizer efficiency in wheat is reduced by ozone pollution
- 2017
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In: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 607-608, s. 876-880
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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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| 10. |
- Buker, P, et al.
(author)
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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.
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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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