Soil - Soil carbon and nitrogen

Title

Experimental drying intensifies burning and carbon losses in a northern peatland.

Reference

Nature Communications, 2011; 2: 514
DOI: 10.1038/ncomms1523

Author(s)

M.R. Turetsky, W.F. Donahue, B.W. Benscoter

Study type

Peer Review Journal

Abstract

For millennia, peatlands have served as an important sink for atmospheric CO2 and today represent a large soil carbon reservoir. While recent land use and wildfires have reduced carbon sequestration in tropical peatlands, the influence of disturbance on boreal peatlands is uncertain, yet it is important for predicting the fate of northern high-latitude carbon reserves. Here we quantify rates of organic matter storage and combustion losses in a boreal peatland subjected to long-term experimental drainage, a portion of which subsequently burned during a wildfire. We show that drainage doubled rates of organic matter accumulation in the soils of unburned plots. However, drainage also increased carbon losses during wildfire ninefold to 16.8±0.2 kg C m−2, equivalent to a loss of more than 450 years of peat accumulation. Interactions between peatland drainage and fire are likely to cause long-term carbon emissions to far exceed rates of carbon uptake, diminishing the northern peatland carbon sink.

Policy theme(s)

Natural hazards >> Wildfires
Soil >> Soil carbon and nitrogen

Keywords

Entry Source:

Selected for Science for Environment Policy News Alert

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http://www.nature.com/ncomms/journal/v2/n10/full/ncomms1523.html
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mrt@uoguelph.ca

Title

Soil water repellency and its implications for organic matter decomposition - is there a link to extreme climatic events?

Reference

Global Change Biology
Volume 17, Issue 8, pages 2640-2656, August 2011
EU funded

Author(s)

Marc-O Goebel, Jorg Bachmann, Markus Reichstein, Ivan Janssens, Georg Guggenberger

Study type

Peer Review Journal

Abstract

Earth system models associate the ongoing global warming with increasing frequency and intensity of extreme events such as droughts and heat waves. The carbon balance of soils may be more sensitive to the impact of such extremes than to homogeneously distributed changes in soil temperature (T_s) or soil water content (θ_s). One parameter influenced by more pronounced drying/rewetting cycles or increases in Ts is the wettability of soils. Results from laboratory and field studies showed that low θ_s, particularly in combination with high Ts can increase soil water repellency (SWR). Recent studies have provided evidence that the stability of soil organic matter (SOM) against microbial decomposition is substantially enhanced in water repellent soils. This review hypothesizes that SWR is an important SOM stabilization mechanism that could become more important because of the increase in extreme events. We discuss wettability-induced changes in soil moisture distribution and in soil aggregate turnover as the main mechanisms explaining the reduced mineralization of SOM with increasing SWR. The creation of preferential flow paths and subsequent uneven penetration of rainwater may cause a long-term reduction of soil water availability, affecting both microorganisms and plants. We conclude that climate change-induced SWR may intensify the effects of climatic drought and thus affects ecosystem processes such as SOM decomposition and plant productivity, as well as changes in vegetation and microbial community structure. Future research on biosphere-climate interactions should consider the effects of increasing SWR on soil moisture and subsequently on both microbial activity and plant productivity, which ultimately determine the overall carbon balance.

Policy theme(s)

Climate change and energy >> Climate change mitigation >> Carbon sinks
Soil >> Soil carbon and nitrogen

Keywords

aggregate stability; carbon cycle; carbon sequestration; climate change; extreme climatic events; hydrophobicity; microbial respiration; soil organic matter; soil water repellency; substrate availability

Entry Source:

Selected for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2011.02414.x/abstract
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goebel@ifbk.uni-hanover.de

Title

Permafrost carbon-climate feedbacks accelerate global warming

Reference

PNAS September 6, 2011 vol. 108 no. 36 14769-14774

Author(s)

Charles D. Koven , Bruno Ringeval, Pierre Friedlingstein, Philippe Ciais, Patricia Cadule, Dmitry Khvorostyanov, Gerhard Krinner, and Charles Tarnocai

Study type

Peer Review Journal

Abstract

Permafrost soils contain enormous amounts of organic carbon, which could act as a positive feedback to global climate change due to enhanced respiration rates with warming. We have used a terrestrial ecosystem model that includes permafrost carbon dynamics, inhibition of respiration in frozen soil layers, vertical mixing of soil carbon from surface to permafrost layers, and CH₄ emissions from flooded areas, and which better matches new circumpolar inventories of soil carbon stocks, to explore the potential for carbon-climate feedbacks at high latitudes. Contrary to model results for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4), when permafrost processes are included, terrestrial ecosystems north of 60°N could shift from being a sink to a source of CO₂ by the end of the 21st century when forced by a Special Report on Emissions Scenarios (SRES) A2 climate change scenario. Between 1860 and 2100, the model response to combined CO₂ fertilization and climate change changes from a sink of 68 Pg to a 27 + -7 Pg sink to 4 + -18 Pg source, depending on the processes and parameter values used. The integrated change in carbon due to climate change shifts from near zero, which is within the range of previous model estimates, to a climate-induced loss of carbon by ecosystems in the range of 25 + -3 to 85 + -16 Pg C, depending on processes included in the model, with a best estimate of a 62 + -7 Pg C loss. Methane emissions from high-latitude regions are calculated to increase from 34 Tg CH₄/y to 41-70 Tg CH₄/y, with increases due to CO₂ fertilization, permafrost thaw, and warming-induced increased CH₄ flux densities partially offset by a reduction in wetland extent.

Policy theme(s)

Climate change and energy >> Climate change mitigation >> Carbon sinks
Climate change and energy >> Greenhouse gas emissions >> Terrestrial emissions
Soil >> Soil carbon and nitrogen

Keywords

carbon cycle:  land surface models: cryosphere: soil organic: matter active layer

Entry Source:

Selected for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.pnas.org/content/108/36/14769.abstract
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cdkoven@lbl.gov

Title

Increased forest ecosystem carbon and nitrogen storage from nitrogen rich bedrock

Reference

Nature 477, 78-81 doi:10.1038/nature10415

Author(s)

Scott L. Morford, Benjamin Z. Houlton & Randy A. Dahlgren

Study type

Peer Review Journal

Abstract

Nitrogen (N) limits the productivity of many ecosystems worldwide, thereby restricting the ability of terrestrial ecosystems to offset the effects of rising atmospheric CO₂ emissions naturally. Understanding input pathways of bioavailable N is therefore paramount for predicting carbon (C) storage on land, particularly in temperate and boreal forests. Paradigms of nutrient cycling and limitation posit that new N enters terrestrial ecosystems solely from the atmosphere. Here we show that bedrock comprises a hitherto overlooked source of ecologically available N to forests. We report that the N content of soils and forest foliage on N-rich metasedimentary rocks (350-950 mg N kg^-1) is elevated by more than 50% compared with similar temperate forest sites underlain by N-poor igneous parent material (30-70 mg N kg^-1). Natural abundance N isotopes attribute this difference to rock-derived N: 15N/14N values for rock, soils and plants are indistinguishable in sites underlain by N-rich lithology, in marked contrast to sites on N-poor substrates. Furthermore, forests associated with N-rich parent material contain on average 42% more carbon in above-ground tree biomass and 60% more carbon in the upper 30cm of the soil than similar sites underlain by N-poor rocks. Our results raise the possibility that bedrock N input may represent an important and overlooked component of ecosystem N and C cycling elsewhere.

Policy theme(s)

Soil >> Soil carbon and nitrogen
Climate change and energy >> Climate change mitigation >> Carbon sinks

Keywords

Earth science, Ecology, Geology and geophysics, Climate science

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.nature.com/nature/journal/v477/n7362/full/nature10415.html  
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slmorford@ucdavis.edu

Title

Reduced N cycling in response to elevated CO₂, warming, and drought in a Danish heathland: Synthesizing results of the CLIMAITE project after two years of treatments.

Reference

Global Change Biology, 2011; 17 (5): 1884 DOI: 10.1111/j.1365-2486.2010.02351.x

Author(s)

Klaus S. Larsen, Louise C. Andresen, Claus Beier, Sven Jonasson, Kristian R. Albert, Per Ambus, Marie F. Arndal, Mette S. Carter, Søren Christensen, Martin Holmstrup, Andreas Ibrom, Jane Kongstad, Leon Van Der Linden, Kristine Maraldo, Anders Michelsen, Teis N. Mikkelsen, Kim Pilegaard, Anders Priemé, Helge Ro-Poulsen, Inger K. Schmidt, Merete B. Selsted, Karen Stevnbak.

Study type

Peer Review Journal

Abstract

Field-scale experiments simulating realistic future climate scenarios are important tools for investigating the effects of current and future climate changes on ecosystem functioning and biogeochemical cycling. We exposed a seminatural Danish heathland ecosystem to elevated atmospheric carbon dioxide (CO₂), warming, and extended summer drought in all combinations. Here, we report on the short-term responses of the nitrogen (N) cycle after 2 years of treatments. Elevated CO₂ significantly affected aboveground stoichiometry by increasing the carbon to nitrogen (C/N) ratios in the leaves of both co-dominant species (Calluna vulgaris and Deschampsia flexuosa), as well as the C/N ratios of Calluna flowers and by reducing the N concentration of Deschampsia litter. Belowground, elevated CO₂ had only minor effects, whereas warming increased N turnover, as indicated by increased rates of microbial NH₄⁺ consumption, gross mineralization, potential nitrification, denitrification and N₂O emissions. Drought reduced belowground gross N mineralization and decreased fauna N mass and fauna N mineralization. Leaching was unaffected by treatments but was significantly higher across all treatments in the second year than in the much drier first year indicating that ecosystem N loss is highly sensitive to changes and variability in amount and timing of precipitation. Interactions between treatments were common and although some synergistic effects were observed, antagonism dominated the interactive responses in treatment combinations, i.e. responses were smaller in combinations than in single treatments. Nonetheless, increased C/N ratios of photosynthetic tissue in response to elevated CO₂, as well as drought-induced decreases in litter N production and fauna N mineralization prevailed in the full treatment combination. Overall, the simulated future climate scenario therefore lead to reduced N turnover, which could act to reduce the potential growth response of plants to elevated atmospheric CO₂ concentration.

Policy theme(s)

Climate change and energy >> Climate change adaptation >> Biodiversity impacts
Soil >> Soil carbon and nitrogen

Keywords

climate driver interactions;C/N ratio;multifactor climate change experiment;N₂O;nitrogen cycling;nitrogen mineralization;soil fauna

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2010.02351.x/full
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klas@risoe.dtu.dk

Title

Comparison of soil CO2 flux between uncleared and cleared windthrow areas in Estonia and Latvia

Reference

Forest Ecology and Management
Volume 262, Issue 2, 15 July 2011, Pages 65-70

Author(s)

Kajar Köster, Ülle Püttsepp and Jukka Pumpanen

Study type

Peer Review Journal

Abstract

Storms can turn a great proportion of forests' assimilation capacity into dead organic matter because of windthrow and thus its role as a carbon sink will be diminished for some time. However, little is known about the magnitude or extent to which storms affect carbon efflux. We compared soil CO2 fluxes in wind-thrown forest stands with different time periods since a storm event, and with different management practices (deadwood cleared or left on-site). This study examined changes in soil CO2 efflux in two windthrow areas in north-eastern Estonia and one area in north-western Latvia, which experienced severe wind storms in the summers of 2001, 2002 and 1967, respectively. We measured soil CO2 fluxes in stands formerly dominated by Norway spruce (Picea abies L. Karst.) with total and partial canopy destruction (all trees or roughly half of the trees in stand damaged by storm), in harvested areas (material removed after the wind storm) and in control areas (no damage by wind). Removal of wind-damaged material decreased instantaneous CO2 flux from the soil surface. The highest instantaneous fluxes were measured in areas with total and partial canopy destruction (0.67 g CO2 m-2 h-1 in both cases) compared with fluxes in the control areas (0.51 g CO2 m-2 h-1), in the new storm-damaged areas where the material was removed (0.57 g CO2 m-2 h-1) and in the old storm-damaged area where wood was left on site (0.55 g CO2 m-2 h-1). The only factor affecting soil CO2 flux was location of the measuring collar (plastic collar with diameter 100 mm, height 50 mm) - either on undamaged forest ground or on the uprooted tree pit, where the mineral soil was exposed after disturbance. New wind-thrown stands where residues are left on site would most likely turn to sources of CO2 for several years until forest regeneration reaches to substantial assimilation rates. New wind-thrown stands where residues are left on site would most likely tend to have elevated CO2 fluxes for several years until forest regeneration reaches to substantial assimilation rates. However, forest managers might be concerned about the amounts of CO2 immediately released into the atmosphere if the harvested logs are burned.

Policy theme(s)

Climate change and energy >> Greenhouse gas emissions >> Terrestrial emissions
Forests >> Forest governance and management
Soil >> Soil carbon

Keywords

Soil respiration, Carbon dioxide, Disturbance, Windthrow management

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.sciencedirect.com/science/article/pii/S0378112710005554
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kajar.koster@emu.ee

Title

Effects of elevated atmospheric CO2, prolonged summer drought and temperature increase on N2O and CH4 fluxes in a temperate heathland

Reference

Soil Biology and Biochemistry
Volume 43, Issue 8, August 2011, Pages 1660-1670

Author(s)

Mette S. Carter, Per Ambus, Kristian R. Albert, Klaus S. Larsen, Michael Andersson, Anders Priemé, Leon van der Linden and Claus Beier

Study type

Peer Review Journal

Abstract

In temperate regions, climate change is predicted to increase annual mean temperature and intensify the duration and frequency of summer droughts, which together with elevated atmospheric carbon dioxide (CO2) concentrations, may affect the exchange of nitrous oxide (N2O) and methane (CH4) between terrestrial ecosystems and the atmosphere. We report results from the CLIMAITE experiment, where the effects of these three climate change parameters were investigated solely and in all combinations in a temperate heathland. Field measurements of N2O and CH4 fluxes took place 1-2 years after the climate change manipulations were initiated. The soil was generally a net sink for atmospheric CH4. Elevated temperature (T) increased the CH4 uptake by on average 10 µg C m-2 h-1, corresponding to a rise in the uptake rate of about 20%. However, during winter elevated CO2 (CO2) reduced the CH4 uptake, which outweighed the positive effect of warming when analyzed across the study period. Emissions of N2O were generally low (<10 µg N m-2 h-1). As single experimental factors, elevated CO2, temperature and summer drought (D) had no major effect on the N2O fluxes, but the combination of CO2 and warming (TCO2) stimulated N2O emission, whereas the N2O emission ceased when CO2 was combined with drought (DCO2). We suggest that these N2O responses are related to increased rhizodeposition under elevated CO2 combined with increased and reduced nitrogen turnover rates caused by warming and drought, respectively. The N2O flux in the multifactor treatment TDCO2 was not different from the ambient control treatment. Overall, our study suggests that in the future, CH4 uptake may increase slightly, while N2O emission will remain unchanged in temperate ecosystems on well-aerated soils. However, we propose that continued exposure to altered climate could potentially change the greenhouse gas flux pattern in the investigated heathland.

Policy theme(s)

Climate change and energy >> Greenhouse gas emissions >> Terrestrial emissions
Soil >> Soil carbon

Keywords

Climate change, Ecosystem manipulation, Greenhouse gas, Methane, Nitrous oxide, Rewetting, Sandy soil, Shrubland, Treatment interaction

Entry Source:

Shortlisted for Science for Environment Policy News Alert

Referred to in EC doc:

N/A

View this study at:

http://www.sciencedirect.com/science/article/pii/S0038071711001477
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Contact the study author at:

mthy@risoe.dtu.dk