| 1. |
- Bresolin de Souza, Karine, et al.
(author)
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Species-specific dinoflagellate vertical distribution in temperature-stratified waters
- 2014
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In: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 161:8, s. 1725-1734
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Journal article (peer-reviewed)abstract
- Thermal stratification is increasing in strength as a result of higher surface water temperature. This could influence the vertical distribution of vertically migrating dinoflagellates. We studied the diel vertical distribution of the dinoflagellates Heterocapsa triquetra and Prorocentrum minimum using stratified laboratory columns with two thermoclines of different strength (Delta TA degrees A = 10 or 17 A degrees C), with below cline temperature of 8 A degrees C. Above the thermocline, nutrient depletion simulated the natural summer conditions in the Baltic Sea. Our study shows that H. triquetra and P. minimum can behave differently in terms of their vertical occurrence, both in space and in time when subjected to thermoclines of different strength. Also, both dinoflagellate species showed species-specific distribution patterns. In the Delta TA degrees A = 10 A degrees C treatment, H. triquetra cells performed a diel vertical migration (DVM) behavior just above the thermocline, but not in the Delta TA degrees A = 17 A degrees C. In the Delta TA degrees A = 17 A degrees C, the cells did not migrate and cell densities in the water column decreased over time. Opposing results were observed for P. minimum, where a DVM pattern was found exclusively below the thermocline of Delta TA degrees A = 17 A degrees C, while in the Delta TA degrees A = 10 A degrees C treatment, no clear DVM pattern was observed, and the highest number of cells were found in the cold bottom water. These results indicate that an increase in thermal stratification can influence species-specific dinoflagellate distribution, behavior, and survival.
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| 2. |
- Hasper, Thomas Berg, et al.
(author)
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Stomatal CO2 responsiveness and photosynthetic capacity of tropical woody species in relation to taxonomy and functional traits
- 2017
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In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 184:1, s. 43-57
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Journal article (peer-reviewed)abstract
- © 2017 The Author(s)Stomatal CO2 responsiveness and photosynthetic capacity vary greatly among plant species, but the factors controlling these physiological leaf traits are often poorly understood. To explore if these traits are linked to taxonomic group identity and/or to other plant functional traits, we investigated the short-term stomatal CO2 responses and the maximum rates of photosynthetic carboxylation (Vcmax) and electron transport (Jmax) in an evolutionary broad range of tropical woody plant species. The study included 21 species representing four major seed plant taxa: gymnosperms, monocots, rosids and asterids. We found that stomatal closure responses to increased CO2 were stronger in angiosperms than in gymnosperms, and in monocots compared to dicots. Stomatal CO2 responsiveness was not significantly related to any of the other functional traits investigated, while a parameter describing the relationship between photosynthesis and stomatal conductance in combined leaf gas exchange models (g1) was related to leaf area-specific plant hydraulic conductance. For photosynthesis, we found that the interspecific variation in Vcmax and Jmax was related to within leaf nitrogen (N) allocation rather than to area-based total leaf N content. Within-leaf N allocation and water use were strongly co-ordinated (r2 = 0.67), such that species with high fractional N investments into compounds maximizing photosynthetic capacity also had high stomatal conductance. We conclude that while stomatal CO2 responsiveness of tropical woody species seems poorly related to other plant functional traits, photosynthetic capacity is linked to fractional within-leaf N allocation rather than total leaf N content and is closely co-ordinated with leaf water use.
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| 3. |
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| 4. |
- Hasper, Thomas Berg, et al.
(author)
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Water use by Swedish boreal forests in a changing climate
- 2016
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In: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 30:5, s. 690-699
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Journal article (peer-reviewed)abstract
- The rising levels of atmospheric carbon dioxide concentration ([CO2]) and temperature have the potential to substantially affect the terrestrial water and energy balance by altering the stomatal conductance and transpiration of trees. Many models assume decreases in stomatal conductance and plant water use under rising [CO2], which has been used as a plausible explanation for the positive global trend in river run-off over the past century. Plant water use is, however, also affected by changes in temperature, precipitation and land use, and there is yet no consensus about the contribution of different drivers to temporal trends of evapotranspiration (ET) and river run-off. In this study, we assessed water-use responses to climate change by using both long-term monitoring and experimental data in Swedish boreal forests. Historical trends and patterns in ET of large-scale boreal landscapes were determined using climate and run-off data from the past 50 years, while explicit tree water-use responses to elevated [CO2] and/or air temperature were examined in a whole-tree chamber experiment using mature Norway spruce (Picea abies (L.) Karst.) trees. The results demonstrated that ET estimated from water budgets at the catchment scale increased by 18% over the past 50 years while run-off did not significantly change. The increase in ET was related to increasing precipitation and a steady increase in forest standing biomass over time. The whole-tree chamber experiment showed that Norway spruce trees did not save water under elevated [CO2] and that experimentally elevated air temperature did not increase transpiration as decreased stomatal conductance cancelled the effect of higher vapour pressure deficit in warmed air. Our findings have important implications for projections of future water use of European boreal coniferous forests, indicating that changes in precipitation and standing biomass are more important than the effects of elevated [CO2] or temperature on transpiration rates.
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| 5. |
- Ljungberg, Peter, et al.
(author)
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Effects of small-scale habitat fragmentation on predator–prey interactions in a temperate sea grass system
- 2013
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In: Marine Biology. - : Springer Science and Business Media LLC. - 0025-3162 .- 1432-1793. ; 160:3, s. 667-675
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Journal article (peer-reviewed)abstract
- During the last decades, fragmentation has become an important issue in ecological research. Habitat fragmentation operates on spatial scales ranging over several magnitudes from patches to landscapes. We focus on small-scale fragmentation effects relevant to animal foraging decision making that could ultimately generate distribution patterns. In a controlled experimental environment, we tested small-scale fragmentation effects in artificial sea grass on the feeding behaviour of juvenile cod (Gadus morhua). Moreover, we examined the influence of fragmentation on the distribution of one of the juvenile cod’s main prey resources, the grass shrimp (Palaemon elegans), in association with three levels of risk provided by cod (no cod, cod chemical cues and actively foraging cod). Time spent by cod within sea grass was lower in fragmented landscapes, but total shrimp consumption was not affected. Shrimp utilised vegetation to a greater extent in fragmented treatments in combination with active predation. We suggest that shrimp choose between sand and vegetation habitats to minimize risk of predation according to cod habitat-specific foraging capacities, while cod aim to maximize prey-dependent foraging rates, generating a habitat-choice game between predator and prey. Moreover, aggregating behaviour in grass shrimp was only found in treatments with active predation. Hence, we argue that both aggregation and vegetation use are anti-predator defence strategies applied by shrimp. We therefore stress the importance of considering small-scale behavioural mechanisms when evaluating consequences from habitat fragmentation on trophic processes in coastal environments.
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| 6. |
- Vårhammar, Angelica, 1988, et al.
(author)
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Photosynthetic temperature responses of tree species in Rwanda: evidence of pronounced negative effects of high temperature in montane rainforest climax species
- 2015
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In: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 206:3, s. 1000-1012
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Journal article (peer-reviewed)abstract
- •The sensitivity of photosynthetic metabolism to temperature has been identified as a key uncertainty for projecting the magnitude of the terrestrial feedback on future climate change. While temperature responses of photosynthetic capacities have been comparatively well investigated in temperate species, the responses of tropical tree species remain unexplored. •We compared the responses of seedlings of native cold-adapted tropical montane rainforest tree species to exotic warm-adapted plantation species, all growing in an intermediate temperature common garden in Rwanda. Leaf gas exchange responses to CO2 at different temperatures (20 – 40 C) were used to assess the temperature responses of biochemical photosynthetic capacities. •Analyses revealed a lower optimum temperature for photosynthetic electron transport rates than for Rubisco carboxylation rates, along with lower electron transport optima in the native cold-adapted than in the exotic warm-adapted species. The photosynthetic optimum temperatures were generally exceeded by daytime peak leaf temperatures, in particular in the native montane rainforest climax species. •This study thus provides evidence of pronounced negative effects of high temperature in tropical trees and indicates high susceptibility of montane rainforest climax species to future global warming.
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