| 61. |
- Lindén, Jenny, et al.
(författare)
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Air pollution removal through deposition on urban vegetation: The importance of vegetation characteristics
- 2023
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Ingår i: Urban Forestry and Urban Greening. - Göteborg : Elsevier BV. - 1618-8667 .- 1610-8167. ; 81
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Tidskriftsartikel (refereegranskat)abstract
- Urban vegetation has the potential to improve air quality as it promotes pollutant deposition and retention. Urban air quality models often include the effect vegetation have on pollution dispersion, however, processes involved in pollution removal by vegetation are often excluded or simplified and does not consider different vegetation characteristics. In this systematic review, we analyze the influence of the large interspecies variation in vegetation characteristics to identify the key factors affecting the removal of the major urban pollutants, particulate matter (PM) and nitrogen dioxide (NO2) from the air through vegetation deposition. The aim is to identify key processes needed to represent vegetation characteristics in urban air quality modelling assessments. We show that PM is mainly deposited to the leaf surface, and thus representation of characteristics affecting the aerodynamics from canopy down to leaf surface are important, such as branch/shoot complexity and leaf size, leaf surface roughness and hairiness. In addition, characteristics affecting PM retention capacity, resuspension and wash-off, include leaf surface roughness, hairiness and wax content. NO2 is mainly deposited through stomatal uptake, and thus stomatal conductance and its responses to environmental conditions are key factors. These include response to solar radiation, vapour pressure deficit and soil moisture. Representation of these vegetation characteristics in urban air quality models could greatly improve our ability to optimize the type and species of urban vegetation from an air quality perspective.
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| 62. |
- Ma, Y. M., et al.
(författare)
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Implementation of trait-based ozone plant sensitivity in the YaleInteractive terrestrial Biosphere model v1.0 to assess global vegetationdamage
- 2023
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Ingår i: Geoscientific Model Development. - 1991-959X. ; 16:8, s. 2261-2276
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Tidskriftsartikel (refereegranskat)abstract
- A major limitation in modeling global ozone (O-3) vegetation damage has long been the reliance on empirical O-3 sensitivity parameters derived from a limited number of species and applied at the level of plant functional types (PFTs), which ignore the large interspecific variations within the same PFT. Here, we present a major advance in large-scale assessments of O-3 plant injury by linking the trait leaf mass per area (LMA) and plant O-3 sensitivity in a broad and global perspective. Application of the new approach and a global LMA map in a dynamic global vegetation model reasonably represents the observed interspecific responses to O-3 with a unified sensitivity parameter for all plant species. Simulations suggest a contemporary global mean reduction of 4.8% in gross primary productivity by O-3, with a range of 1.1 %-12.6% for varied PFTs. Hotspots with damage > 10% are found in agricultural areas in the eastern US, western Europe, eastern China, and India, accompanied by moderate to high levels of surface O-3. Furthermore, we simulate the distribution of plant sensitivity to O-3, which is highly linked with the inherent leaf trait trade-off strategies of plants, revealing high risks for fast-growing species with low LMA, such as crops, grasses, and deciduous trees.
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| 63. |
- Metcalfe, Daniel B., et al.
(författare)
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Patchy field sampling biases understanding of climate change impacts across the Arctic
- 2018
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Ingår i: Nature Ecology and Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 2:9, s. 1443-1448
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Tidskriftsartikel (refereegranskat)abstract
- Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.
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| 64. |
- Mills, Gina, 1959, et al.
(författare)
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Closing the global ozone yield gap: Quantification and cobenefits for multistress tolerance
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:10, s. 4869-4893
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Tidskriftsartikel (refereegranskat)abstract
- Increasing both crop productivity and the tolerance of crops to abiotic and biotic stresses is a major challenge for global food security in our rapidly changing climate. For the first time, we show how the spatial variation and severity of tropospheric ozone effects on yield compare with effects of other stresses on a global scale, and discuss mitigating actions against the negative effects of ozone. We show that the sensitivity to ozone declines in the order soybean > wheat > maize > rice, with genotypic variation in response being most pronounced for soybean and rice. Based on stomatal uptake, we estimate that ozone (mean of 2010–2012) reduces global yield annually by 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively (the “ozone yield gaps”), adding up to 227 Tg of lost yield. Our modelling shows that the highest ozone-induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the United States. Crucially, we also show that the same areas are often also at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. In a solution-focussed analysis of these results, we provide a crop ideotype with tolerance of multiple stresses (including ozone) and describe how ozone effects could be included in crop breeding programmes. We also discuss altered crop management approaches that could be applied to reduce ozone impacts in the shorter term. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap.
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| 65. |
- Mills, Gina, 1959, et al.
(författare)
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Ozone pollution will compromise efforts to increase global wheat production
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:8, s. 3560-3574
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Tidskriftsartikel (refereegranskat)abstract
- Introduction of high-performing crop cultivars and crop/soil water management practices that increase the stomatal uptake of carbon dioxide and photosynthesis will be instrumental in realizing the United Nations Sustainable Development Goal (SDG) of achieving food security. To date, however, global assessments of how to increase crop yield have failed to consider the negative effects of tropospheric ozone, a gaseous pollutant that enters the leaf stomatal pores of plants along with carbon dioxide, and is increasing in concentration globally, particularly in rapidly developing countries. Earlier studies have simply estimated that the largest effects are in the areas with the highest ozone concentrations. Using a modelling method that accounts for the effects of soil moisture deficit and meteorological factors on the stomatal uptake of ozone, we show for the first time that ozone impacts on wheat yield are particularly large in humid rain-fed and irrigated areas of major wheat-producing countries (e.g. United States, France, India, China and Russia). Averaged over 2010-2012, we estimate that ozone reduces wheat yields by a mean 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, corresponding to some 85 Tg (million tonnes) of lost grain. Total production losses in developing countries receiving Official Development Assistance are 50% higher than those in developed countries, potentially reducing the possibility of achieving UN SDG2. Crucially, our analysis shows that ozone could reduce the potential yield benefits of increasing irrigation usage in response to climate change because added irrigation increases the uptake and subsequent negative effects of the pollutant. We show that mitigation of air pollution in a changing climate could play a vital role in achieving the above-mentioned UN SDG, while also contributing to other SDGs related to human health and well-being, ecosystems and climate change.
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| 66. |
- Mujawamariya, M., et al.
(författare)
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Climate sensitivity of tropical trees along an elevation gradient in rwanda
- 2018
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Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 9:10
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Tidskriftsartikel (refereegranskat)abstract
- Elevation gradients offer excellent opportunities to explore the climate sensitivity of vegetation. Here, we investigated elevation patterns of structural, chemical, and physiological traits in tropical tree species along a 1700–2700 m elevation gradient in Rwanda, central Africa. Two early-successional (Polyscias fulva, Macaranga kilimandscharica) and two late-successional (Syzygium guineense, Carapa grandiflora) species that are abundant in the area and present along the entire gradient were investigated. We found that elevation patterns in leaf stomatal conductance (gs), transpiration (E), net photosynthesis (An), and water-use efficiency were highly season-dependent. In the wet season, there was no clear variation in gs or An with elevation, while E was lower at cooler high-elevation sites. In the dry season, gs, An, and E were all lower at drier low elevation sites. The leaf-to-air temperature difference was smallest in P. fulva, which also had the highest gs and E. Water-use efficiency (An/E) increased with elevation in the wet season, but not in the dry season. Leaf nutrient ratios indicated that trees at all sites are mostly P limited and the N:P ratio did not decrease with increasing elevation. Our finding of strongly decreased gas exchange at lower sites in the dry season suggests that both transpiration and primary production would decline in a climate with more pronounced dry periods. Furthermore, we showed that N limitation does not increase with elevation in the forests studied, as otherwise most commonly reported for tropical montane forests.
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| 67. |
- Mujawamariya, Myriam, et al.
(författare)
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Complete or overcompensatory thermal acclimation of leaf dark respiration in African tropical trees
- 2021
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 229:5, s. 2548-61
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Tidskriftsartikel (refereegranskat)abstract
- © 2020 The Authors New Phytologist © 2020 New Phytologist Foundation Tropical climates are getting warmer, with pronounced dry periods in large areas. The productivity and climate feedbacks of future tropical forests depend on the ability of trees to acclimate their physiological processes, such as leaf dark respiration (Rd), to these new conditions. However, knowledge on this is currently limited due to data scarcity. We studied the impact of growth temperature on Rd and its dependency on net photosynthesis (An), leaf nitrogen (N) and phosphorus (P) contents, and leaf mass per unit area (LMA) in 16 early-successional (ES) and late-successional (LS) tropical tree species in multispecies plantations along an elevation gradient (Rwanda TREE project). Moreover, we explored the effect of drought on Rd in one ES and one LS species. Leaf Rd at 20°C decreased at warmer sites, regardless if it was expressed per unit leaf area, mass, N or P. This acclimation resulted in an 8% and a 28% decrease in Rd at prevailing nighttime temperatures in trees at the intermediate and warmest sites, respectively. Moreover, drought reduced Rd, particularly in the ES species and at the coolest site. Thermal acclimation of Rd is complete or overcompensatory and independent of changes in leaf nutrients or LMA in African tropical trees.
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| 68. |
- Mujawamariya, Myriam, et al.
(författare)
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Contrasting warming responses of photosynthesis in early- and late-successional tropical trees
- 2023
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Ingår i: Tree physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 43:7, s. 1104-17
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Tidskriftsartikel (refereegranskat)abstract
- The productivity and climate feedbacks of tropical forests depend on tree physiological responses to warmer and, over large areas, seasonally drier conditions. However, knowledge regarding such responses is limited due to data scarcity. We studied the impact of growth temperature on net photosynthesis (A(n)), maximum rates of Rubisco carboxylation at 25 degrees C (V-cmax25), stomatal conductance (g(s)) and the slope parameter of the stomatal conductance-photosynthesis model (g(1)), in 10 early successional (ES) and 8 late-successional (LS) tropical tree species grown at three sites along an elevation gradient in Rwanda, differing by 6.8 degrees C in daytime ambient air temperature. The effect of seasonal drought on A(n) was also investigated. We found that warm climate decreased wet-season A(n) in LS species, but not in ES species. Values of V-cmax25 were lower at the warmest site across both successional groups, and A(n) and V-cmax25 were higher in ES compared with LS species. Stomatal conductance exhibited no significant site differences and g(1) was similar across both sites and successional groups. Drought strongly reduced A(n) at warmer sites but not at the coolest montane site and this response was similar in both ES and LS species. Our results suggest that warming has negative effects on leaf-level photosynthesis in LS species, while both LS and ES species suffer photosynthesis declines in a warmer climate with more pronounced droughts. The contrasting responses of A(n) between successional groups may lead to shifts in species' competitive balance in a warmer world, to the disadvantage of LS trees.
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| 69. |
- Ntawuhiganayo, E. B., et al.
(författare)
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Traits controlling shade tolerance in tropical montane trees
- 2020
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 40:2, s. 183-197
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Tidskriftsartikel (refereegranskat)abstract
- Tropical canopies are complex, with multiple canopy layers and pronounced gap dynamics contributing to their high species diversity and productivity. An important reason for this complexity is the large variation in shade tolerance among different tree species. At present, we lack a clear understanding of which plant traits control this variation, e.g., regarding the relative contributions of whole-plant versus leaf traits or structural versus physiological traits. We investigated a broad range of traits in six tropical montane rainforest tree species with different degrees of shade tolerance, grown under three different radiation regimes (under the open sky or beneath sparse or dense canopies). The two distinct shade-tolerant species had higher fractional biomass in leaves and branches while shade-intolerant species invested more into stems, and these differences were greater under low radiation. Leaf respiration and photosynthetic light compensation point did not vary with species shade tolerance, regardless of radiation regime. Leaf temperatures in open plots were markedly higher in shade-tolerant species due to their low transpiration rates and large leaf sizes. Our results suggest that interspecific variation in shade tolerance of tropical montane trees is controlled by species differences in whole-plant biomass allocation strategy rather than by difference in physiological leaf traits determining leaf carbon balance at low radiation.
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| 70. |
- Ntirugulirwa, Bonaventure, et al.
(författare)
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Thermophilisation of Afromontane forest stands demonstrated in an elevation gradient experiment
- 2023
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Ingår i: Biogeosciences. - 1810-6277. ; 20:24
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Tidskriftsartikel (refereegranskat)abstract
- The response of tropical trees and tree communities to climate change is crucial for the carbon storage and biodiversity of the terrestrial biosphere. Trees in tropical montane rain forests (TMFs) are considered particularly vulnerable to climate change, but this hypothesis remains poorly evaluated due to data scarcity. To reduce the knowledge gap in the response of TMF trees to warming, we established a field experiment along a 1300–2400 m elevation gradient as a proxy for warming in Rwanda. Seedling-size trees of 20 species native to montane forests in eastern and central Africa were planted in multi-species plots at three sites along the gradient. They have overlapping distributions but primarily occur in either transitional rain forests (∼ 1600–2000 m a. s. l.) or mid-elevation TMFs (∼ 2000–3000 m a. s. l. ), with both early- (ES) and late-successional (LS) species represented in each elevation origin group. Tree growth (diameter and height) and survival were monitored regularly over 2 years. We found that ES species, especially from lower elevations, grew faster at warmer sites, while several of the LS species, especially from higher elevations, did not respond or grew slower. Moreover, a warmer climate increased tree mortality in LS species, but not much in ES species. ES species with transitional rain forest origin strongly increased proportional to stand basal area at warmer sites, while TMF species declined, suggesting that lower-elevation ES species will have an advantage over higher-elevation species in a warming climate. The risk of higher-elevation and LS species of becoming outcompeted by lower-elevation and ES species due to a thermophilisation response in a warmer climate has important implications for biodiversity and carbon storage of Afromontane forests.
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