| 1. |
- Igamberdiev, Abir U, et al.
(författare)
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Photorespiration Contributes to Stomatal Regulation and Carbon Isotope Fractionation: A Study with Barley, Potato and Arabidopsis Plants Deficient in Glycine Decarboxylase
- 2004
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Ingår i: Photosynthesis Research. ; 81, s. 139-152
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Tidskriftsartikel (refereegranskat)abstract
- The rates of respiration in light and darkness, C i/C a and carbon isotope fractionation were investigated in glycine decarboxylase-deficient plants of barley, potato and Arabidopsis thaliana grown in climate chambers with controlled light intensity, temperature, humidity, irradiation and different CO2 concentrations (360, 700 and 1400 µl l–1) and compared to the wild-type plants. All photorespiration-impaired plants exhibited higher C i/C a and corresponding lower apparent water-use efficiencies, which were more expressed under high irradiance and elevated temperature. The mutants were depleted in 13C as compared to the wild-type plants, with a difference of up to 6permil following growth in 360 µl l–1 CO2. We determined the carbon isotope content at different CO2 concentrations to calculate the contribution of both C i/C a and photorespiration for 13C/12C fractionation. The direct effect of photorespiration was in the range of 0.7–1.0permil, from which we calculated the value of fractionation at the site of glycine decarboxylation as being 10–13permil, which is in agreement with the previously reported carbon isotope discrimination exerted by the glycine decarboxylase. Respiratory rates, particularly in the light, were increased in the glycine decarboxylase mutants. The necessity of the maintenance of a high CO2 concentration near the site of carboxylation in chloroplasts in plants deficient in photorespiratory enzymes, requires an increased opening of the stomata with a corresponding decrease in water-use efficiency. It is concluded that photorespiration participates in the regulation of C i/C a and contributes to carbon isotope fractionation, both via effects on stomata and via discrimination of 13C in the glycine decarboxylase reaction.
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| 2. |
- Vestergård, Mette, et al.
(författare)
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Enhanced priming of old, not new soil carbon at elevated atmospheric CO2
- 2016
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 100, s. 140-148
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Tidskriftsartikel (refereegranskat)abstract
- Rising atmospheric CO2 concentrations accompanied by global warming and altered precipitation patterns calls for assessment of long-term effects of these global changes on carbon (C) dynamics in terrestrial ecosystems, as changes in net C exchange between soil and atmosphere will impact the atmospheric CO2 concentration profoundly. In many ecosystems, including the heath/grassland system studied here, increased plant production at elevated CO2 increase fresh C input from litter and root exudates to the soil and concurrently decrease soil N availability. Supply of labile C to the soil may accelerate the decomposition of soil organic C (SOC), a phenomenon termed 'the priming effect', and the priming effect is most pronounced at low soil N availability. Hence, we hypothesized that priming of SOC decomposition in response to labile C addition would increase in soil exposed to long-term elevated CO2 exposure. Further, we hypothesized that long-term warming would enhance SOC priming rates, whereas drought would decrease the priming response. We incubated soil from a long-term, full-factorial climate change field experiment, with the factors elevated atmospheric CO2 concentration, warming and prolonged summer drought with either labile C (sucrose) or water to assess the impact of labile C on SOC dynamics. We used sucrose with a 13C/12C signature that is distinct from that of the native SOC, which allowed us to assess the contribution of these two C sources to the CO2 evolved. Sucrose induced priming of SOC, and the priming response was higher in soil exposed to long-term elevated CO2 treatment. Drought tended to decrease the priming response, whereas long-term warming did not affect the level of priming significantly. We were also able to assess whether SOC-derived primed C in elevated CO2 soil was assimilated before or after the initiation of the CO2 treatment 8 years prior to sampling, because CO2 concentrations were raised by fumigating the experimental plots with pure CO2 that was 13C-depleted compared to ambient CO2. Surprisingly, we conclude that sucrose addition primed decomposition of relatively old SOC fractions, i.e. SOC assimilated more than 8 years before sampling.
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| 3. |
- Andersen, Emil Alexander Sherman, et al.
(författare)
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Nitrogen isotopes reveal high N retention in plants and soil of old Norse and Inuit deposits along a wet-dry arctic fjord transect in Greenland
- 2020
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Ingår i: Plant and Soil. - : Springer. - 0032-079X .- 1573-5036. ; 455:1-2, s. 241-255
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Plant growth in the Arctic is often nutrient limited due to temperature constraints on decomposition and low atmospheric input of nitrogen (N). Local hotspots of nutrient enrichment found in up to 4000-year-old archaeological deposits can be used to explore the recycling and long-term retention of nutrients in arctic ecosystems.Methods: We investigated old Inuit and Norse deposits (known as middens) and adjacent tundra ecosystems along a wet-dry fjord gradient in western Greenland to explore the isotopic fingerprinting of plant and soil carbon and nitrogen (C-13/C-12 and(15)N/N-14) derived from human presence.Results: At all locations we observed a significant isotopic fingerprint in soil and plant N related to human deposits. This demonstrates a century-long legacy of past human habitation on plant and soil characteristics and indicates a surprisingly high N retention in these ecosystems. This is consistent with the significantly higher plant biomass in areas with archaeological deposits.Conclusion: Vegetation composition and N in plants and soils displayed marked differences along the wet-dry fjord gradient. Furthermore, the profound nutrient enrichment and organic matter accumulation in archaeological deposits compared to surrounding tundra demonstrates a century-long legacy of past habitation on plant and soil characteristics as well as efficient N cycling with surprisingly limited N loss.
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| 4. |
- Andresen, Louise C., 1974, et al.
(författare)
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Moderate nitrogen retention in temperate heath ecosystem after elevated CO2, drought and warming through 7years
- 2023
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Ingår i: European Journal of Soil Science. - 1351-0754 .- 1365-2389. ; 74:4
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) dynamic is one of the main controlling factors of responses to climate change in N-limited terrestrial ecosystems, which rely on nutrient re-cycling and retention. In this study we investigate the N partitioning in ecosystem compartments of a grassland heath, and the impact of multiple climate change factors on long-term N retention after 15N pulse labelling. The impacts of elevated carbon dioxide (eCO2), warming and drought and the treatments in combination on ecosystem N retention was investigated in a field scale manipulation experiment. A six-year time-course was assessed by pulse-labelling with the stable N isotope 15N and by sampling after 1 day, 1 year and 6years. After the six years we observed that the total ecosystem retained 42 % of the amended 15N across treatments (recovery of the amended 15N in the pool). The fate of the applied 15N was mainly stabilisation in soil, with 36 % recovery, while the plant compartment and microbial biomass each retained only 1-2 % of the added 15N. This suggests a moderate retention of N, for all treatments, as compared to similar long-term studies of forest ecosystems. A decreased ammonium and vegetation N pool combined with higher 15N retention in the soil at eCO2 treatments suggests that eCO2 promoted processes that immobilize N in soil, while warming counteracted this when combined with eCO2. Drought treatments contrastingly increased the vegetation N pool. We conclude that as the organic soil layer has the main capacity for N storage in a temperate heathland-grassland, it is important for buffering nutrient availability and maintaining a resilient ecosystem. However, the full treatment combination of drought, warming and eCO2 did not differ in 15N recovery from the controls, suggesting unchanged long-term consequences of climate change on retention of pulse added N in this ecosystem.
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| 5. |
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| 6. |
- Björsne, Anna-Karin, 1983, et al.
(författare)
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Effect of climate change on soil nitrogen dynamics in a heathland
- 2012
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Ingår i: BIOGEOMON 2012, Northport, Maine, USA, 2012-07-16.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Climate change is likely to affect all levels of the global biosphere. Nitrogen (N) is limiting for net primary production (NPP) in most terrestrial ecosystems and therefore a crucial factor for the ecosystem response to climate change. The hypothesis of progressive nitrogen limitation (PNL) predicts that if NPP is stimulated by elevated CO2 (eCO2), N will become limiting in the ecosystems over time, since the plants will sequester more N with increased carbon uptake (Luo et al. 2004). However, PNL tells nothing of the response of soil N cycling to eCO2. If turnover rates of N accelerate together with decreasing N losses it would lead to increased soil N availability, which would alleviate PNL (Rütting et al. 2010). The N cycle response to a changing climate is however still poorly understood. Only a few studies have investigated how ecosystems are affected by exposure to multiple climate factors and if responses are variable over time. This study is part of CLIMAITE (Climate change effects on biological processes in terrestrial ecosystems), simulating the projected climate conditions for Denmark in 2075 (Mikkelsen et al. 2008). We have investigated how the gross mineralization rates in a heathland are affected by climate change after 2 and 5 years of manipulation. The study site was exposed to three climate factors; eCO2, increased temperature and prolonged summer drought, both single and in combination, in a total of eight different treatments. We have measured the gross mineralization rates with stable isotope techniques in 2010 and compared with mineralization data from 2007. The aim of the study is to understand how climate change affects soil mineralization and if responses on soil nitrogen turnover vary over time of exposure to climate change. Results will be discussed in the light of changes in physico-chemical soil properties as well as compared to other studies.
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| 7. |
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| 8. |
- Holmstrup, Martin, et al.
(författare)
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Long-term and realistic global change manipulations had low impact on diversity of soil biota in temperate heathland
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- In a dry heathland ecosystem we manipulated temperature (warming), precipitation (drought) and atmospheric concentration of CO2 in a full-factorial experiment in order to investigate changes in below-ground biodiversity as a result of future climate change. We investigated the responses in community diversity of nematodes, enchytraeids, collembolans and oribatid mites at two and eight years of manipulations. We used a structural equation modelling (SEM) approach analyzing the three manipulations, soil moisture and temperature, and seven soil biological and chemical ariables. The analysis revealed a persistent and positive effect of elevated CO2 on litter C:N ratio. After two years of treatment, the fungi to bacteria ratio was increased by warming, and the diversities within oribatid mites, collembolans and nematode groups were all affected by elevated CO2 mediated through increased litter C:N ratio. After eight years of treatment, however, the CO2-increased litter C:N ratio did not influence the diversity in any of the four fauna groups. The number of significant correlations between treatments, food source quality, and soil biota diversities was reduced from six to three after two and eight years, respectively. These results suggest a remarkable resilience within the soil biota against global climate change treatments in the long term.
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| 9. |
- Rasmussen, L. H., et al.
(författare)
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Modelling impacts of lateral N flows and seasonal warming on an arctic footslope ecosystem N budget and N2O emissions based on species-level responses
- 2022
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Ingår i: Biogeochemistry. - : Springer Nature. - 0168-2563 .- 1573-515X. ; 158:2, s. 195-213
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Tidskriftsartikel (refereegranskat)abstract
- Future Arctic tundra primary productivity and vegetation community composition will partly be determined by nitrogen (N) availability in a warmer climate. N mineralization rates are predicted to increase in both winter and summer, but because N demand and –mobility varies across seasons, the fate of mineralized N remains uncertain. N mineralized in winter is released in a “pulse” upon snowmelt and soil thaw, with the potential for lateral redistribution in the landscape. In summer, the release is into an active rhizosphere with high local biological N demand. In this study, we investigated the ecosystem sensitivity to increased lateral N input and near-surface warming, respectively and in combination, with a numerical ecosystem model (CoupModel) parameterized to simulate ecosystem biogeochemistry for a tundra heath ecosystem in West Greenland. Both measurements and model results indicated that plants were poor utilizers of increased early-season lateral N input, indicating that higher winter N mineralization rates may have limited impact on plant growth and carbon (C) sequestration for a hillslope ecosystem. The model further suggested that, although deciduous shrubs were the plant type with overall most lateral N gain, evergreen shrubs appear to have a comparative advantage utilizing early-season N. In contrast, near-surface summer warming increased plant biomass and N uptake, moving N from soil to plant N pools, and offered an advantage to deciduous plants. Neither simulated high lateral N fluxes nor near-surface soil warming suggests that mesic tundra heaths will be important sources of N2O under warmer conditions. Our work highlights how winter and summer warming may play different roles in tundra ecosystem N and C budgets depending on plant community composition.
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| 10. |
- Rasmussen, Laura Helene, 1990, et al.
(författare)
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Nitrogen immobilization could link extreme winter warming events to Arctic browning
- 2024
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Ingår i: Soil Biology and Biochemistry. - 0038-0717. ; 191
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Tidskriftsartikel (refereegranskat)abstract
- Arctic extreme winter warming events (WW events) have increased in frequency with climate change. WW events have been linked to damaged tundra vegetation (“Arctic browning”), but the mechanisms that link episodic winter thaw to plant damage in summer are not fully understood. We suggest that one mechanism is microbial N immobilization during the WW event, which leads to a smaller release of winter-mineralized N in spring and therefore more N limitation for vegetation in summer. We tested this hypothesis in a Western Greenlandic Low arctic tundra, where we experimentally simulated a 6 day field-scale extreme WW event and 1) used stable isotopes to trace the movement of N as a consequence of the WW event, 2) measured the effect of a WW event on spring N release in top soils in the laboratory, and 3) measured the carry-over effect on summer aboveground vegetation C/N ratio in tundra subject to a WW event. Our results show that soil mineral N released by a WW event followed by soil thaw is taken up by microbes and stored in the soil, whereas vascular plants acquired almost none, and significant amounts were lost to leaching and gaseous emissions. As soils thawed in spring, we saw weak but not significant evidence (P = 0.067) for a larger N release over the first month of spring thaw in Control soils compared to WW event soils, although not significantly. A weak signal (P = 0.07) linked WW event treatment to higher summer C/N ratios in evergreen shrubs, whereas deciduous shrubs were not affected. We conclude that our results did not show significant evidence for WW events causing Arctic browning via N immobilization and summer N limitation, but that we had indications (P < 0.1) which merits further testing of the theory in various tundra types and with repeated WW events. Evergreen shrubs could be especially sensitive to winter N immobilization, with implications for future vegetation community composition and tundra C storage.
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| 11. |
- Rasmussen, L. H., et al.
(författare)
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Nitrogen transport in a tundra landscape : the effects of early and late growing season lateral N inputs on arctic soil and plant N pools and N2O fluxes
- 2022
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Ingår i: Biogeochemistry. - : Springer Nature. - 0168-2563 .- 1573-515X. ; 157:1, s. 69-84
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Tidskriftsartikel (refereegranskat)abstract
- Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N2O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic.
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| 12. |
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