The changing carbon balance of tundra ecosystems: results from a vertically-resolved peatland biosphere model

Abstract An estimated 1700 Pg of carbon is frozen in the Arctic permafrost and the fate of this carbon is unclear because of the complex interaction of biophysical, ecological and biogeochemical processes that govern the Arctic carbon budget. Two key processes determining the region’s long-term carbon budget are: (i) carbon uptake through increased plant growth, and (ii) carbon release through increased heterotrophic respiration due to warmer soils. Previous predictions for how these two opposing carbon fluxes may change in the future have varied greatly, indicating that improved understanding of these processes and their feedbacks is critical for advancing our predictive ability for the fate of Arctic peatlands. In this study, we implement and analyze a vertically-resolved model of peatland soil carbon into a cohort-based terrestrial biosphere model to improve our understanding of how on-going changes in climate are altering the Arctic carbon budget. A key feature of the formulation is that accumulation of peat within the soil column modifies its texture, hydraulic conductivity, and thermal conductivity, which, in turn influences resulting rates of heterotrophic respiration within the soil column. Analysis of the model at three eddy covariance tower sites in the Alaskan tundra shows that the vertically-resolved soil column formulation accurately captures the zero-curtain phenomenon, in which the temperature of soil layers remain at or near 0 °C during fall freezeback due to the release of latent heat, is critical to capturing observed patterns of wintertime respiration. We find that significant declines in net ecosystem productivity (NEP) occur starting in 2013 and that these declines are driven by increased heterotrophic respiration arising from increased precipitation and warming. Sensitivity analyses indicate that the cumulative NEP over the decade responds strongly to the estimated soil carbon stock and more weakly to vegetation abundance at the beginning of the simulation.

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A study of the role of wetlands in defining spatial patterns of near-surface (top 1 m) soil carbon in the Northern Latitudes

Biogeosciences Discussions ◽

10.5194/bgd-11-17967-2014 ◽

2014 ◽

Vol 11 (12) ◽

pp. 17967-18002

Author(s):

E. M. Blyth ◽

R. Oliver ◽

N. Gedney

Keyword(s):

Soil Carbon ◽

Spatial Patterns ◽

Land Surface ◽

Surface Soil ◽

Heterotrophic Respiration ◽

The Arctic ◽

Near Surface ◽

Northern Latitudes ◽

The Relationship

Abstract. A study of two observation-based maps (the Harmonised World Soil Database, HWSD and the Northern Circumpolar Soil Carbon Database, NCSCD) of the surface (1 m) soil carbon in the Northern Latitudes (containing the Arctic and Boreal regions) reveal that, although the amounts of carbon estimated to be present in this region are very uncertain, the patterns are robust: both maps have soil carbon maxima that coincide with the major wetlands in the region, as described in the Global Lakes and Wetlands Database, GLWD. In fact, the relationship between near-surface soil carbon and the presence of wetlands is stronger than the relationship with soil temperature and vegetation productivity. These relationships are explored using the land surface model of the UK Hadley Centre GCM: JULES (Joint UK Land Environment Simulator). The model is run to represent conditions at the end of the 20th century. Observed vegetation and phenology are used to define the vegetation, the physical properties of organic soils are represented, the fine-scale topography of the region is included in the parameterisation of the hydrology and as a result the GPP and location of the wetlands of the region are reasonably well simulated using JULES. Despite this, the soil carbon simulated by the model does not reveal the same patterns or the correlation with the wetland regions that are present in the data. This suggests that the model does not represent sufficiently strongly the suppression of heterotrophic respiration in saturated conditions. A simple adjustment to the JULES model was made whereby the heterotrophic respiration was reduced by the fraction of the grid that is modelled to be saturated. In effect, for the saturated areas the respiration was zero. This adjustment represents a simple experiment to establish the role of wetlands in defining the spatial patterns of near-surface soil carbon. The results were an improved predicted spatial pattern of soil carbon, with an increase in the correlation between soil carbon and wetlands although not as strong as suggested by the analysis of the data. This may be because the size of the wetlands was underestimated by the model. The study suggests that land surface models in general, and JULES in particular, need to establish a stronger moderation of soil respiration in saturated conditions in order that future climate controls on wetlands in the Northern Latitudes will result in the correct changes in soil carbon and carbon emissions.

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Fifty years of contrasted residue management of an agricultural crop: Impacts on the soil carbon budget and on soil heterotrophic respiration

Agriculture Ecosystems & Environment ◽

10.1016/j.agee.2013.01.006 ◽

2013 ◽

Vol 167 ◽

pp. 52-59 ◽

Cited By ~ 32

Author(s):

Pauline Buysse ◽

Christian Roisin ◽

Marc Aubinet

Keyword(s):

Soil Carbon ◽

Carbon Budget ◽

Heterotrophic Respiration ◽

Residue Management ◽

Agricultural Crop ◽

Soil Heterotrophic Respiration

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Microbial decomposition processes and vulnerable arctic soil organic carbon in the 21st century

Biogeosciences ◽

10.5194/bg-15-5621-2018 ◽

2018 ◽

Vol 15 (18) ◽

pp. 5621-5634 ◽

Cited By ~ 2

Author(s):

Junrong Zha ◽

Qianlai Zhuang

Keyword(s):

Soil Carbon ◽

20Th Century ◽

21St Century ◽

Carbon Budget ◽

Carbon Sink ◽

The Arctic ◽

Microbial Decomposition ◽

New Model ◽

Terrestrial Ecosystem Model ◽

Rcp 8.5

Abstract. Various levels of representations of biogeochemical processes in current biogeochemistry models contribute to a large uncertainty in carbon budget quantification. Here, we present an uncertainty analysis with a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), into which detailed microbial mechanisms were incorporated. Ensemble regional simulations with the new model (MIC-TEM) estimated that the carbon budget of the arctic ecosystems is 76.0±114.8 Pg C during the 20th century, i.e., -3.1±61.7 Pg C under the RCP 2.6 scenario and 94.7±46 Pg C under the RCP 8.5 scenario during the 21st century. Positive values indicate the regional carbon sink while negative values are a source to the atmosphere. Compared to the estimates using a simpler soil decomposition algorithm in TEM, the new model estimated that the arctic terrestrial ecosystems stored 12 Pg less carbon over the 20th century, i.e., 19 and 30 Pg C less under the RCP 8.5 and RCP 2.6 scenarios, respectively, during the 21st century. When soil carbon within depths of 30, 100, and 300 cm was considered as initial carbon in the 21st century simulations, the region was estimated to accumulate 65.4, 88.6, and 109.8 Pg C, respectively, under the RCP 8.5 scenario. In contrast, under the RCP 2.6 scenario, the region lost 0.7, 2.2, and 3 Pg C, respectively, to the atmosphere. We conclude that the future regional carbon budget evaluation largely depends on whether or not adequate microbial activities are represented in earth system models and on the sizes of soil carbon considered in model simulations.

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The moisture response of soil heterotrophic respiration: interaction with soil properties

Biogeosciences ◽

10.5194/bg-9-1173-2012 ◽

2012 ◽

Vol 9 (3) ◽

pp. 1173-1182 ◽

Cited By ~ 142

Author(s):

F. E. Moyano ◽

N. Vasilyeva ◽

L. Bouckaert ◽

F. Cook ◽

J. Craine ◽

...

Keyword(s):

Soil Moisture ◽

Soil Properties ◽

Soil Carbon ◽

Empirical Support ◽

Heterotrophic Respiration ◽

Water Dynamics ◽

Organic Carbon Content ◽

Soil Carbon Stock ◽

Biogeochemical Models ◽

Soil Heterotrophic Respiration

Abstract. Soil moisture is of primary importance for predicting the evolution of soil carbon stocks and fluxes, both because it strongly controls organic matter decomposition and because it is predicted to change at global scales in the following decades. However, the soil functions used to model the heterotrophic respiration response to moisture have limited empirical support and introduce an uncertainty of at least 4% in global soil carbon stock predictions by 2100. The necessity of improving the representation of this relationship in models has been highlighted in recent studies. Here we present a data-driven analysis of soil moisture-respiration relations based on 90 soils. With the use of linear models we show how the relationship between soil heterotrophic respiration and different measures of soil moisture is consistently affected by soil properties. The empirical models derived include main effects and moisture interaction effects of soil texture, organic carbon content and bulk density. When compared to other functions currently used in different soil biogeochemical models, we observe that our results can correct biases and reconcile differences within and between such functions. Ultimately, accurate predictions of the response of soil carbon to future climate scenarios will require the integration of soil-dependent moisture-respiration functions coupled with realistic representations of soil water dynamics.

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The moisture response of soil heterotrophic respiration: interaction with soil properties

Biogeosciences Discussions ◽

10.5194/bgd-8-11577-2011 ◽

2011 ◽

Vol 8 (6) ◽

pp. 11577-11599 ◽

Cited By ~ 6

Author(s):

F. E. Moyano ◽

N. Vasilyeva ◽

L. Bouckaert ◽

F. Cook ◽

J. Craine ◽

...

Keyword(s):

Soil Moisture ◽

Soil Properties ◽

Soil Carbon ◽

Empirical Support ◽

Heterotrophic Respiration ◽

Water Dynamics ◽

Organic Carbon Content ◽

Soil Carbon Stock ◽

Biogeochemical Models ◽

Soil Heterotrophic Respiration

Abstract. Soil moisture is of primary importance for predicting the evolution of soil carbon stocks and fluxes, both because it strongly controls organic matter decomposition and because it is predicted to change at global scales in the following decades. However, the soil functions used to model the heterotrophic respiration response to moisture have limited empirical support and introduce an uncertainty of at least 4 % in global soil carbon stock predictions by 2100. The necessity of improving the representation of this relationship in models has been highlighted in recent studies. Here we present a data-driven analysis of soil moisture-respiration relations based on 90 soils. With the use of linear models we show how the relationship between soil heterotrophic respiration and different measures of soil moisture is consistently affected by soil properties. The empirical models derived include main and moisture interaction effects of soil texture, organic carbon content and bulk density. When compared to other functions currently used in different soil biogeochemical models, we observe that our results can correct biases and reconcile differences within and between such functions. Ultimately, accurate predictions of the response of soil carbon to future climate scenarios will require the integration of soil-dependent moisture-respiration functions coupled with realistic representations of soil water dynamics.

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Microbial decomposition processes and vulnerable Arctic soil organic carbon in the 21st century

10.5194/bg-2018-241 ◽

2018 ◽

Author(s):

Junrong Zha ◽

Qianlai Zhuang

Keyword(s):

Soil Carbon ◽

20Th Century ◽

21St Century ◽

Carbon Budget ◽

Terrestrial Ecosystem ◽

Terrestrial Ecosystems ◽

The Arctic ◽

Microbial Decomposition ◽

Terrestrial Ecosystem Model ◽

Rcp 8.5

Abstract. Inadequate representation of biogeochemical processes in current biogeochemistry models results in a large uncertainty in carbon budget quantification. Here, detailed microbial mechanisms were incorporated into a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM). Ensemble regional simulations with the model estimated the Arctic ecosystem carbon budget is 76.0 ± 114.8 Pg C during the 20th century, −3.1 ± 61.7 Pg C under the RCP 2.6 scenario and a sink of 94.7 ± 46 Pg C under the RCP 8.5 scenario during the 21st century. Compared to the estimates using a simpler soil decomposition algorithm in TEM, the new model estimated that the Arctic terrestrial ecosystems stored 12 Pg less carbon over the 20th century, 19 Pg C and 30 Pg C less under the RCP 8.5 and RCP 2.6 scenarios, respectively, during the 21st century. When soil carbon within depths 30 cm, 100 cm and 300 cm was considered as initial carbon in the 21st century simulations, the region was estimated to accumulate 65.4, 88.6, and 109.8 Pg C, respectively, under the RCP 8.5 scenario. In contrast, under the RCP 2.6 scenario, the region lost 0.7, 2.2, and 3 Pg C, respectively, to the atmosphere. We conclude that the future regional carbon budget evaluation largely depends on whether or not the adequate microbial activities are represented in earth system models and the sizes of soil carbon considered in model simulations.

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Modeling soil organic carbon dynamics in temperate forests using Yasso07

10.5194/bg-2018-219 ◽

2018 ◽

Author(s):

Zhun Mao ◽

Delphine Derrien ◽

Markus Didion ◽

Jari Liski ◽

Thomas Eglin ◽

...

Keyword(s):

Soil Carbon ◽

Carbon Stock ◽

Temperate Forests ◽

National Level ◽

Carbon Dynamics ◽

Carbon Stocks ◽

Sensitivity Analyses ◽

Global Changes ◽

Soil Carbon Stock ◽

Carbon Quality

Abstract. Facing global changes, modeling and predicting the dynamics of soil carbon stock of forest ecosystems is vital but challenging work. Yasso07 is considered as one of the most promising models for such a purpose. We aim at examining the prediction accuracy of Yasso07 on soil carbon dynamics over the whole French metropolitan territory at a decennial time scale. We used the dataset from 101 RENECOFOR sites network, which encompass most of the French temperate forests. The data include (i) measured yearly litter quantity from aboveground organs part from 1994 to 2008, and soil carbon stocks twice at an interval of ca. 15 years (early 1990s versus around 2010). Using Yasso07, we simulated the stock changes (t C ha−1 yr−1) per site and compared them with the measured ones. We carried out meta-analyses to reveal the variability in litter biochemistry between different tree organs for conifers and broadleaves. We also performed sensitivity analyses to explore Yasso07’s sensitivity to inputs, including litter carbon quality and initial carbon stocks. At the national level, the simulated annual carbon stock changes (ACC, +0.45 ± 0.09 t C ha−1 year−1, mean ± standard error) stayed in the same order of magnitude with the observed ones (+0.34 ± 0.06 t C ha−1 year−1). The correlation between predicted and measured ACC remained weak (R²

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