| 1. |
- 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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| 2. |
- 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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| 3. |
- Clifton, O. E., et al.
(författare)
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Influence of Dynamic Ozone Dry Deposition on Ozone Pollution
- 2020
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Ingår i: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 125:8
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Cox, A. J. F., et al.
(författare)
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Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change
- 2023
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 238:6, s. 2329-2344
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Crous, K. Y., et al.
(författare)
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Temperature responses of photosynthesis and respiration in evergreen trees from boreal to tropical latitudes
- 2022
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 234:2, s. 353-374
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Dusenge, Mirindi Eric, 1986, et al.
(författare)
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Limited thermal acclimation of photosynthesis in tropical montane tree species
- 2021
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 27:19, s. 4860-4878
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Ellsworth, D. S., et al.
(författare)
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Convergence in phosphorus constraints to photosynthesis in forests around the world
- 2022
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Ely, K. S., et al.
(författare)
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A reporting format for leaf-level gas exchange data and metadata
- 2021
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Ingår i: Ecological Informatics. - : Elsevier BV. - 1574-9541. ; 61
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Gardner, A., et al.
(författare)
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Optimal stomatal theory predicts CO2 responses of stomatal conductance in both gymnosperm and angiosperm trees
- 2022
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 237:4, s. 1229-41
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Tidskriftsartikel (refereegranskat)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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| 10. |
- Johansson, Karin S L, et al.
(författare)
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Genetic controls of short- and long-term stomatal CO2 responses in Arabidopsis thaliana
- 2020
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Ingår i: Annals of botany. - : Oxford University Press (OUP). - 1095-8290 .- 0305-7364. ; 126:1, s. 179-190
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Tidskriftsartikel (refereegranskat)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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| 11. |
- Konarska, Janina, 1986, et al.
(författare)
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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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Ingår i: Landscape and Urban Planning. - 0169-2046. ; 240
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Tidskriftsartikel (refereegranskat)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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| 12. |
- Li, Pin, et al.
(författare)
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Combining carbon and oxygen isotopic signatures to identify ozone-induced declines in tree water use efficiency
- 2021
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 41:12, s. 2234-2244
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Tidskriftsartikel (refereegranskat)abstract
- Ground-level ozone (O3) pollution affects the plant carbon and water balance, but the relative contributions of impaired photosynthesis and the loss of stomatal functioning to the O3-induced reductions in water use efficiency (WUE) remain unclear. We combined the leaf stable dual isotopic signatures of carbon (δ13C) and oxygen (δ18O) with related instantaneous gas exchange performance to determine the effects of O3 dose on the net photosynthetic rate (An), stomatal conductance (gs) and intrinsic WUE (iWUE = An/gs) in four tree species (one being a hybrid) exposed to five O3 levels. The iWUE declined for each step increase in O3 level, reflecting progressive loss of the coupling between leaf carbon gain and water loss. In ambient compared to charcoal-filtered air, the decreased iWUE was associated with reductions in both An and gs (i.e., decreased δ13C and increased δ18O). In elevated O3 treatments, however, the iWUE declines were caused by reduced An at constant or increased gs. The results show that the dual isotope approach provides a robust way to gather time-integrated information on how O3 pollution affects leaf gas exchange. Our study highlights that O3-induced decoupling between photosynthesis and stomatal regulation causes large and progressive declines in the WUE of forest trees, demonstrating the need for incorporating this, hitherto unaccounted, effect into vegetation models.
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| 13. |
- 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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| 14. |
- 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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| 15. |
- 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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| 16. |
- 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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| 17. |
- 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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| 18. |
- 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, s. 5125-5149
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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 1300–2400m 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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| 19. |
- Ostwald, Madelene, et al.
(författare)
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”En ineffektiv åtgärd i klimatarbetet”
- 2021
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Ingår i: Svenska Dagbladet. - 1101-2412.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Vi välkomnar repliken från Carbon Capture Companys vd. Vi, EU, Sveriges regering och Christoffer Bonde delar målet att främja ett starkt och lönsamt skogsbruk som bidrar till klimatarbetet både genom upptag av växthusgaser och minskade utsläpp. Vad vi ställer oss kritiska till är den klimatkompensation som just nu lanseras av företag som Carbon Capture Company, eftersom vi anser att den är dyr, kortsiktig och ineffektiv.
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| 20. |
- Ostwald, Madelene, 1966-, et al.
(författare)
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”Klimatkompensation i svensk skog en dålig idé”
- 2021
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Ingår i: Svenska Dagbladet. - 1101-2412.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Företag som ser sig om efter åtgärder för att minska sin klimatpåverkan och samtidigt stärka sitt varumärke bör undvika klimatkompensation i svenska skogar. Det skriver sex forskare.
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| 21. |
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| 22. |
- Tarvainen, Lasse, 1977, et al.
(författare)
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Handling the heat - photosynthetic thermal stress in tropical trees.
- 2022
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Ingår i: The New phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 233:1, s. 236-50
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Tidskriftsartikel (refereegranskat)abstract
- Warming climate increases the risk for harmful leaf temperatures in terrestrial plants, causing heat stress and loss of productivity. The heat sensitivity may be particularly high in equatorial tropical tree species adapted to a thermally stable climate. Thermal thresholds of the photosynthetic system of sun-exposed leaves were investigated in three tropical montane tree species native to Rwanda with different growth and water use strategies (Harungana montana, Syzygium guineense and Entandrophragma exselsum). Measurements of chlorophyll fluorescence, leaf gas exchange, morphology, chemistry and temperature were made at three common gardens along an elevation/temperature gradient. Heat tolerance acclimated to maximum leaf temperature (Tleaf ) across the species. At the warmest sites, the thermal threshold for normal function of photosystem II was exceeded in the species with the highest Tleaf despite their higher heat tolerance. This was not the case in the species with the highest transpiration rates and lowest Tleaf . The results point to two differently effective strategies for managing thermal stress: tolerance through physiological adjustment of leaf osmolality and thylakoid membrane lipid composition, or avoidance through morphological adaptation and transpiratory cooling. More severe photosynthetic heat stress in low-transpiring montane climax species may result in a competitive disadvantage compared to high-transpiring pioneer species with more efficient leaf cooling.
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| 23. |
- Torres Jimenez, Maria Fernanda, et al.
(författare)
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Functional and historical drivers of leaf shape evolution in Palms (Arecaceae)
- 2023
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Ingår i: Global Ecology and Biogeography. - 1466-822X. ; 32:9, s. 1495-1507
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Tidskriftsartikel (refereegranskat)abstract
- Aim Leaves display a remarkable variety of shapes, each with potential ecological advantages in specific climates. While the relations between leaf shape and either climate or height have been relatively well studied in eudicots, the macroecological drivers of shape remain poorly known in monocots. Here, we investigated the associations between climate and plant height with the evolution of leaf shape in a clade with high species and morphological diversity.Location Global.Time period Cretaceous to contemporary.Major taxa studied Palms (Arecaceae).Methods We apply a Bayesian phylogenetic mixed model to test for associations between climate and leaf shape (all - entire-leaved, pinnate-dissected, palmate-dissected and costapalmate). We further reconstruct the ancestral leaf shape using multistate speciation and extinction models and compare the frequency of shapes with global temperatures through time.Results We find that plant height associates with dissected leaves and that annual precipitation associates with pinnate shapes. The ancestral leaf shape is unclear, but early diversification was dominated by pinnate-dissected palms, which has remained the most species-rich form of leaves throughout palm history.Main Conclusions Palms that are tall and live in humid regions are more likely to have pinnate leaves. Through geological time scales, temperature did not play an obvious role in determining leaf shapes. This study contributes to our understanding of how the diversity of leaf shapes is linked to biological and climatic factors.
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| 24. |
- Wittemann, Maria, et al.
(författare)
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Temperature acclimation of net photosynthesis and its underlying component processes in four tropical tree species
- 2022
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Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 42:6, s. 1188-1202
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Tidskriftsartikel (refereegranskat)abstract
- The effect of temperature change on leaf physiology has been extensively studied in temperate trees and to some extent in boreal and tropical tree species. While increased temperature typically stimulates leaf CO2 assimilation and tree growth in high-altitude ecosystems, tropical species are often negatively affected. These trees may operate close to their temperature optima and have a limited thermal acclimation capacity due to low seasonal and historical variation in temperature. To test this hypothesis, we studied the extent to which the temperature sensitivities of leaf photosynthesis and respiration acclimate to growth temperature in four common African tropical tree species. Tree seedlings native to different altitudes and therefore adapted to different growth temperatures were cultivated at three different temperatures in climate-controlled chambers. We estimated the acclimation capacity of the temperature sensitivities of light-saturated net photosynthesis, the maximum rates of Rubisco carboxylation (V-cmax) and thylakoid electron transport (J), and dark respiration. Leaf thylakoid membrane lipid composition, nitrogen content and leaf mass per area were also analyzed. Our results showed that photosynthesis in tropical tree species acclimated to higher growth temperatures, but that this was weakest in the species originating from the coolest climate. The temperature optimum of J acclimated significantly in three species and variation in J was linked to changes in the thylakoid membrane lipid composition. For V-cmax, there was only evidence of significant acclimation of optimal temperature in the lowest elevation species. Respiration acclimated to maintain homeostasis at growth temperature in all four species. Our results suggest that the lowest elevation species is better physiologically adapted to acclimate to high growth temperatures than the highest elevation species, indicating a potential shift in competitive balance and tree community composition to the disadvantage of montane tree species in a warmer world.
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| 25. |
- Xu, Y. S., et al.
(författare)
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Variations in leaf anatomical characteristics drive the decrease of mesophyll conductance in poplar under elevated ozone
- 2023
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 29:10, s. 2804-2823
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Tidskriftsartikel (refereegranskat)abstract
- Decline in mesophyll conductance (g(m)) plays a key role in limiting photosynthesis in plants exposed to elevated ozone (O-3). Leaf anatomical traits are known to influence g(m), but the potential effects of O-3-induced changes in leaf anatomy on g(m) have not yet been clarified. Here, two poplar clones were exposed to elevated O-3. The effects of O-3 on the photosynthetic capacity and anatomical characteristics were assessed to investigate the leaf anatomical properties that potentially affect g(m). We also conducted global meta-analysis to explore the general response patterns of g(m) and leaf anatomy to O-3 exposure. We found that the O-3-induced reduction in g(m) was critical in limiting leaf photosynthesis. Changes in liquid-phase conductance rather than gas-phase conductance drive the decline in g(m) under elevated O-3,O- and this effect was associated with thicker cell walls and smaller chloroplast sizes. The effects of O-3 on palisade and spongy mesophyll cell traits and their contributions to g(m) were highly genotype-dependent. Our results suggest that, while anatomical adjustments under elevated O-3 may contribute to defense against O-3 stress, they also cause declines in g(m) and photosynthesis. These results provide the first evidence of anatomical constraints on g(m) under elevated O-3.
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| 26. |
- Ziegler, Camille, et al.
(författare)
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Contrasting Dependencies of Photosynthetic Capacity on Leaf Nitrogen in Early- and Late-Successional Tropical Montane Tree Species
- 2020
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Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Differences in photosynthetic capacity among tree species and tree functional types are currently assumed to be largely driven by variation in leaf nutrient content, particularly nitrogen (N). However, recent studies indicate that leaf N content is often a poor predictor of variation in photosynthetic capacity in tropical trees. In this study, we explored the relative importance of area-based total leaf N content (N-tot) and within-leaf N allocation to photosynthetic capacity versus light-harvesting in controlling the variation in photosynthetic capacity (i.e.V-cmax,J(max)) among mature trees of 12 species belonging to either early (ES) or late successional (LS) groups growing in a tropical montane rainforest in Rwanda, Central Africa. Photosynthetic capacity at a common leaf temperature of 25x2da;C (i.e. maximum rates of Rubisco carboxylation,V(cmax25)and of electron transport,J(max25)) was higher in ES than in LS species (+ 58% and 68% forV(cmax25)andJ(max25), respectively). While N(tot)did not significantly differ between successional groups, the photosynthetic dependency on N(tot)was markedly different. In ES species,V(cmax25)was strongly and positively related to N(tot)but this was not the case in LS species. However, there was no significant trade-off between relative leaf N investments in compounds maximizing photosynthetic capacity versus compounds maximizing light harvesting. Both leaf dark respiration at 25x2da;C (+ 33%) and, more surprisingly, apparent photosynthetic quantum yield (+ 35%) was higher in ES than in LS species. Moreover, R(d25)was positively related to N(tot)for both ES and LS species. Our results imply that efforts to quantify carbon fluxes of tropical montane rainforests would be improved if they considered contrasting within-leaf N allocation and photosynthetic N(tot)dependencies between species with different successional strategies.
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