| 1. |
- Maes, S.L., et al.
(author)
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Environmental drivers of increased ecosystem respiration in a warming tundra
- 2024
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In: Nature. - : Springer Nature. - 0028-0836 .- 1476-4687. ; 629:8010, s. 105-113
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Journal article (peer-reviewed)abstract
- Arctic and alpine tundra ecosystems are large reservoirs of organic carbon. Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere. The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain. This hampers the accuracy of global land carbon–climate feedback projections. Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9–2.0 °C] in air and 0.4 °C [CI 0.2–0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22–38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration.
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| 2. |
- Hollister, R. D., et al.
(author)
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A review of open top chamber (OTC) performance across the ITEX Network
- 2023
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In: Arctic Science. - : Canadian Science Publishing. - 2368-7460. ; 9:2, s. 331-344
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Journal article (peer-reviewed)abstract
- Open top chambers (OTCs) were adopted as the recommended warming mechanism by the International Tundra Experiment network in the early 1990s. Since then, OTCs have been deployed across the globe. Hundreds of papers have reported the im-pacts of OTCs on the abiotic environment and the biota. Here, we review the impacts of the OTC on the physical environment, with comments on the appropriateness of using OTCs to characterize the response of biota to warming. The purpose of this review is to guide readers to previously published work and to provide recommendations for continued use of OTCs to under -stand the implications of warming on low stature ecosystems. In short, the OTC is a useful tool to experimentally manipulate temperature; however, the characteristics and magnitude of warming varies greatly in different environments; therefore, it is important to document chamber performance to maximize the interpretation of biotic response. When coupled with long-term monitoring, warming experiments are a valuable means to understand the impacts of climate change on natural ecosystems.
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| 3. |
- Karlsson, Tomas, et al.
(author)
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Leaf-Scale Study of Biogenic Volatile Organic Compound Emissions from Willow (Salix spp.) Short Rotation Coppices Covering Two Growing Seasons
- 2021
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In: Atmosphere. - : MDPI AG. - 2073-4433. ; 12:11
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Journal article (peer-reviewed)abstract
- In Europe, willow (Salix spp.) trees have been used commercially since the 1980s at a large scale to produce renewable energy. While reducing fossil fuel needs, growing short rotation coppices (SRCs), such as poplar or willow, may have a high impact on local air quality as these species are known to produce high amounts of isoprene, which can lead to the production of tropospheric ozone (O-3). Here, we present a long-term leaf-scale study of biogenic volatile organic compound (BVOC) emissions from a Swedish managed willow site with the aim of providing information on the seasonal variability in BVOC emissions during two growing seasons, 2015-2016. Total BVOC emissions during these two seasons were dominated by isoprene (> 96% by mass) and the monoterpene (MT) ocimene. The average standardized (STD, temperature of 30 & DEG;C and photosynthetically active radiation of 1000 mu mol m(-2) s(-1)) emission rate for isoprene was 45.2 (& PLUSMN;42.9, standard deviation (SD)) mu g g(dw)(-1) h(-1). Isoprene varied through the season, mainly depending on the prevailing temperature and light, where the measured emissions peaked in July 2015 and August 2016. The average STD emission for MTs was 0.301 (& PLUSMN;0.201) mu g g(dw)(-1) h(-1) and the MT emissions decreased from spring to autumn. The average STD emission for sesquiterpenes (SQTs) was 0.103 (& PLUSMN;0.249) mu g g(dw)(-1) h(-1), where caryophyllene was the most abundant SQT. The measured emissions of SQTs peaked in August both in 2015 and 2016. Non-terpenoid compounds were grouped as other VOCs (0.751 & PLUSMN; 0.159 mu g g(dw)(-1) h(-1)), containing alkanes, aldehydes, ketones, and other compounds. Emissions from all the BVOC groups decreased towards the end of the growing season. The more sun-adapted leaves in the upper part of the plantation canopy emitted higher rates of isoprene, MTs, and SQTs compared with more shade-adapted leaves in the lower canopy. On the other hand, emissions of other VOCs were lower from the upper part of the canopy compared with the lower part. Light response curves showed that ocimene and alpha-farnesene increased with light but only for the sun-adapted leaves, since the shade-adapted leaves did not emit ocimene and alpha-farnesene. An infestation with Melampsora spp. likely induced high emissions of, e.g., hexanal and nonanal in August 2015. The results from this study imply that upscaling BVOC emissions with model approaches should account for seasonality and also include the canopy position of leaves as a parameter to allow for better estimates for the regional and global budgets of ecosystem emissions.
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| 4. |
- Pascual, Didac, et al.
(author)
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The missing pieces for better future predictions in subarctic ecosystems: A Torneträsk case study
- 2021
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In: Ambio. - : Springer. - 0044-7447 .- 1654-7209. ; 50:2, s. 375-392
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Research review (peer-reviewed)abstract
- Arctic and subarctic ecosystems are experiencing substantial changes in hydrology, vegetation, permafrost conditions, and carbon cycling, in response to climatic change and other anthropogenic drivers, and these changes are likely to continue over this century. The total magnitude of these changes results from multiple interactions among these drivers. Field measurements can address the overall responses to different changing drivers, but are less capable of quantifying the interactions among them. Currently, a comprehensive assessment of the drivers of ecosystem changes, and the magnitude of their direct and indirect impacts on subarctic ecosystems, is missing. The Torneträsk area, in the Swedish subarctic, has an unrivalled history of environmental observation over 100 years, and is one of the most studied sites in the Arctic. In this study, we summarize and rank the drivers of ecosystem change in the Torneträsk area, and propose research priorities identified, by expert assessment, to improve predictions of ecosystem changes. The research priorities identified include understanding impacts on ecosystems brought on by altered frequency and intensity of winter warming events, evapotranspiration rates, rainfall, duration of snow cover and lake-ice, changed soil moisture, and droughts. This case study can help us understand the ongoing ecosystem changes occurring in the Torneträsk area, and contribute to improve predictions of future ecosystem changes at a larger scale. This understanding will provide the basis for the future mitigation and adaptation plans needed in a changing climate.
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| 5. |
- Tang, J., et al.
(author)
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Acclimation of Biogenic Volatile Organic Compound Emission From Subarctic Heath Under Long-Term Moderate Warming
- 2018
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In: Journal of Geophysical Research - Biogeosciences. - 2169-8953. ; 123:1, s. 95-105
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Journal article (peer-reviewed)abstract
- Biogenic volatile organic compound (BVOC) emissions from subarctic ecosystems have shown to increase drastically in response to a long-term temperature increase of only 2°C. We assessed whether this increase takes place already after 3 years of warming and how the increase changes over time. To test this, we measured BVOC emissions and CO2 fluxes in a field experiment on a subarctic wet heath, where ecosystem plots were subjected to passive warming by open top chambers for 3 (OTC3) or 13 years (OTC13) or were kept as unmanipulated controls. Already after 3 years of moderate temperature increase of 1–2°C, warming increased the emissions of isoprene (five- to sixfold) and monoterpenes (three- to fourfold) from the subarctic heath. The several-fold higher BVOC emissions in the warmed plots are likely a result of increased vegetation biomass and altered vegetation composition as a shift in the species coverage was observed already after 3 years of warming. Warming also increased gross ecosystem production and ecosystem respiration, but the increases were much lower than those for BVOCs. Our results demonstrate that the strong BVOC responses to warming already appeared after 3 years, and the BVOC and CO2 fluxes had acclimated to this warming after 3 years, showing no differences with another 10 years of warming. This finding has important implications for predicting CO2 and BVOC fluxes in subarctic ecosystems.
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| 6. |
- Tang, J., et al.
(author)
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Process Understanding of Soil BVOC Fluxes in Natural Ecosystems : A Review
- 2019
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In: Reviews of Geophysics. - 8755-1209. ; 57:3, s. 966-986
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Research review (peer-reviewed)abstract
- Biogenic volatile organic compounds (BVOCs) can be released from soils to the atmosphere through microbial decomposition of plant residues or soil organic carbon, root emission, evaporation of litter-stored BVOCs, and other physical processes. Soils can also act as a sink of BVOCs through biotic and abiotic uptake. Currently, the source and sink capabilities of soils have not been explicitly accounted for in global BVOC estimates from the terrestrial biosphere. In this review, we summarize the current knowledge of soil BVOC processes and aim to propose a generic framework for modelling soil BVOCs based on current understanding and data availability. To achieve this target, we start by reviewing measured sources and sinks of soil BVOCs and summarize commonly reported compounds. Next, we strive to disentangle the drivers for the underlying biotic and abiotic processes. We have ranked the list of compounds, known to be emitted from soils, based on our current understanding of how each process controls emission and uptake. We then present a modelling framework to describe soil BVOC emissions. The proposed framework is an important step toward initializing modelling exercises related to soil BVOC fluxes. Finally, we also provide suggestions for measurements needed to separate individual processes, as well as explore long-term and large-scale patterns in soil BVOC fluxes.
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