Carbon isotopic measurements from coastal zone protected forests in northern China: Soil carbon decomposition assessment and its influencing factors

Abstract. Priming of soil carbon decomposition encompasses different processes through which the decomposition of native (already present) soil organic matter is amplified through the addition of new organic matter, with new inputs typically being more labile than the native soil organic matter. Evidence for priming comes from laboratory and field experiments, but to date there is no estimate of its impact at global scale and under the current anthropogenic perturbation of the carbon cycle. Current soil carbon decomposition models do not include priming mechanisms, thereby introducing uncertainty when extrapolating short-term local observations to ecosystem and regional to global scale. In this study we present a simple conceptual model of decomposition priming, called PRIM, able to reproduce laboratory (incubation) and field (litter manipulation) priming experiments. Parameters for this model were first optimized against data from 20 soil incubation experiments using a Bayesian framework. The optimized parameter values were evaluated against another set of soil incubation data independent from the ones used for calibration and the PRIM model reproduced the soil incubations data better than the original, CENTURY-type soil decomposition model, whose decomposition equations are based only on first-order kinetics. We then compared the PRIM model and the standard first-order decay model incorporated into the global land biosphere model ORCHIDEE (Organising Carbon and Hydrology In Dynamic Ecosystems). A test of both models was performed at ecosystem scale using litter manipulation experiments from five sites. Although both versions were equally able to reproduce observed decay rates of litter, only ORCHIDEE–PRIM could simulate the observed priming (R2 = 0.54) in cases where litter was added or removed. This result suggests that a conceptually simple and numerically tractable representation of priming adapted to global models is able to capture the sign and magnitude of the priming of litter and soil organic matter.

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Can we model observed soil carbon changes from a dense inventory? A case study over England and Wales using three versions of the ORCHIDEE ecosystem model (AR5, AR5-PRIM and O-CN)

Geoscientific Model Development ◽

10.5194/gmd-6-2153-2013 ◽

2013 ◽

Vol 6 (6) ◽

pp. 2153-2163 ◽

Cited By ~ 10

Author(s):

B. Guenet ◽

F. E. Moyano ◽

N. Vuichard ◽

G. J. D. Kirk ◽

P. H. Bellamy ◽

...

Keyword(s):

Soil Carbon ◽

Net Primary Productivity ◽

Soil Depth ◽

Carbon Mineralization ◽

Ecosystem Model ◽

Climate Trends ◽

England And Wales ◽

Carbon Decomposition ◽

Plant Soil ◽

Carbon Losses

Abstract. A widespread decrease of the topsoil carbon content was observed over England and Wales during the period 1978–2003 in the National Soil Inventory (NSI), amounting to a carbon loss of 4.44 Tg yr−1 over 141 550 km2. Subsequent modelling studies have shown that changes in temperature and precipitation could only account for a small part of the observed decrease, and therefore that changes in land use and management and resulting changes in heterotrophic respiration or net primary productivity were the main causes. So far, all the models used to reproduce the NSI data have not accounted for plant–soil interactions and have only been soil carbon models with carbon inputs forced by data. Here, we use three different versions of a process-based coupled soil–vegetation model called ORCHIDEE (Organizing Carbon and Hydrology in Dynamic Ecosystems), in order to separate the effect of trends in soil carbon input from soil carbon mineralization induced by climate trends over 1978–2003. The first version of the model (ORCHIDEE-AR5), used for IPCC-AR5 CMIP5 Earth System simulations, is based on three soil carbon pools defined with first-order decomposition kinetics, as in the CENTURY model. The second version (ORCHIDEE-AR5-PRIM) built for this study includes a relationship between litter carbon and decomposition rates, to reproduce a priming effect on decomposition. The last version (O-CN) takes into account N-related processes. Soil carbon decomposition in O-CN is based on CENTURY, but adds N limitations on litter decomposition. We performed regional gridded simulations with these three versions of the ORCHIDEE model over England and Wales. None of the three model versions was able to reproduce the observed NSI soil carbon trend. This suggests either that climate change is not the main driver for observed soil carbon losses or that the ORCHIDEE model even with priming or N effects on decomposition lacks the basic mechanisms to explain soil carbon change in response to climate, which would raise a caution flag about the ability of this type of model to project soil carbon changes in response to future warming. A third possible explanation could be that the NSI measurements made on the topsoil are not representative of the total soil carbon losses integrated over the entire soil depth, and thus cannot be compared with the model output.

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Early Holocene Changes in Lake Level and Productivity in Lake Malawi as Interpreted from Oxygen and Carbon Isotopic Measurements of Authigenic Carbonates

The Limnology, Climatology and Paleoclimatology of the East African Lakes ◽

10.1201/9780203748978-26 ◽

2019 ◽

pp. 475-493 ◽

Cited By ~ 3

Author(s):

R.D. Ricketts ◽

T.C. Johnson

Keyword(s):

Lake Level ◽

Lake Malawi ◽

Early Holocene ◽

Authigenic Carbonates ◽

Carbon Isotopic ◽

Isotopic Measurements

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The implications of microbial and substrate limitation for the fates of carbon in different organic soil horizon types: a mechanistically based model analysis

Biogeosciences Discussions ◽

10.5194/bgd-11-2227-2014 ◽

2014 ◽

Vol 11 (2) ◽

pp. 2227-2266 ◽

Cited By ~ 2

Author(s):

Y. He ◽

Q. Zhuang ◽

J. W. Harden ◽

A. D. McGuire ◽

Z. Fan ◽

...

Keyword(s):

Soil Carbon ◽

Microbial Activity ◽

Size Variation ◽

Pool Size ◽

Soil Horizon ◽

Biogeochemical Processes ◽

Soil Horizons ◽

Model Framework ◽

Carbon Decomposition ◽

Decomposition Models

Abstract. The large magnitudes of soil carbon stocks provide potentially large feedbacks to climate changes, highlighting the need to better understand and represent the environmental sensitivity of soil carbon decomposition. Most soil carbon decomposition models rely on empirical relationships omitting key biogeochemical mechanisms and their response to climate change is highly uncertain. In this study, we developed a multi-layer mechanistically based soil decomposition model framework for boreal forest ecosystems. A global sensitivity analysis was conducted to identify dominating biogeochemical processes and to highlight structural limitations. Our results indicate that substrate availability (limited by soil water diffusion and substrate quality) is likely to be a major constraint on soil decomposition in the fibrous horizon (40–60% of SOC pool size variation), while energy limited microbial activity in the amorphous horizon exerts a predominant control on soil decomposition (>70% of SOC pool size variation). Elevated temperature alleviated the energy constraint of microbial activity most notably in amorphous soils; whereas moisture only exhibited a marginal effect on dissolved substrate supply and microbial activity. Our study highlights the different decomposition properties and underlying mechanisms of soil dynamics between fibrous and amorphous soil horizons. Soil decomposition models should consider explicitly representing different boreal soil horizons and soil-microbial interactions to better characterize biogeochemical processes in boreal ecosystems. A more comprehensive representation of critical biogeochemical mechanisms of soil moisture effects may be required to improve the performance of the soil model we analyzed in this study.

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Oscillatory behavior of two nonlinear microbial models of soil carbon decomposition

Biogeosciences ◽

10.5194/bg-11-1817-2014 ◽

2014 ◽

Vol 11 (7) ◽

pp. 1817-1831 ◽

Cited By ~ 39

Author(s):

Y. P. Wang ◽

B. C. Chen ◽

W. R. Wieder ◽

M. Leite ◽

B. E. Medlyn ◽

...

Keyword(s):

Stability Analysis ◽

Microbial Biomass ◽

Soil Carbon ◽

Nonlinear Model ◽

Linear Models ◽

Nonlinear Models ◽

Oscillatory Behavior ◽

Carbon Pools ◽

Carbon Decomposition ◽

Pool Model

Abstract. A number of nonlinear models have recently been proposed for simulating soil carbon decomposition. Their predictions of soil carbon responses to fresh litter input and warming differ significantly from conventional linear models. Using both stability analysis and numerical simulations, we showed that two of those nonlinear models (a two-pool model and a three-pool model) exhibit damped oscillatory responses to small perturbations. Stability analysis showed the frequency of oscillation is proportional to √(&varepsilon;−1−1) Ks/Vs in the two-pool model, and to √(&varepsilon;−1−1) Kl/Vl in the three-pool model, where &varepsilon; is microbial growth efficiency, Ks and Kl are the half saturation constants of soil and litter carbon, respectively, and /Vs and /Vl are the maximal rates of carbon decomposition per unit of microbial biomass for soil and litter carbon, respectively. For both models, the oscillation has a period of between 5 and 15 years depending on other parameter values, and has smaller amplitude at soil temperatures between 0 and 15 °C. In addition, the equilibrium pool sizes of litter or soil carbon are insensitive to carbon inputs in the nonlinear model, but are proportional to carbon input in the conventional linear model. Under warming, the microbial biomass and litter carbon pools simulated by the nonlinear models can increase or decrease, depending whether &varepsilon; varies with temperature. In contrast, the conventional linear models always simulate a decrease in both microbial and litter carbon pools with warming. Based on the evidence available, we concluded that the oscillatory behavior and insensitivity of soil carbon to carbon input are notable features in these nonlinear models that are somewhat unrealistic. We recommend that a better model for capturing the soil carbon dynamics over decadal to centennial timescales would combine the sensitivity of the conventional models to carbon influx with the flexible response to warming of the nonlinear model.

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