Abstract
Abstract. The large amount of soil carbon in boreal forest ecosystems has the potential to influence the climate system if released in large quantities in response to warming. Thus, there is a 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 microbial explicit soil decomposition model framework for boreal forest ecosystems. A thorough 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 soil organic carbon (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 forest 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.
Highlights
Decomposition of the large stocks of soil organic matter in northern high latitude ecosystems in response to warming is one of the largest potential feedbacks to climate change (Bond-Lamberty and Thomson, 2010; Tarnocai et al, 2009)
Enzyme pool (ENZ) in general exhibited similar sensitivity patterns with that of microbial biomass C pool (MIC) and soil organic C pool (SOC) (Fig. 5b). These results indicate that microbial assimilation and substrate availability are important factors for amorphous soil, while substrate availability superimposed over microbial assimilation are the most important controls of decomposition in fibrous soil
We presented a mechanistically based soil C dynamic model and evaluated the sensitivity of SOC decomposition to temperature and moisture effects in fibrous and amorphous soil horizons via a global sensitivity analysis
Summary
Decomposition of the large stocks of soil organic matter in northern high latitude ecosystems in response to warming is one of the largest potential feedbacks to climate change (Bond-Lamberty and Thomson, 2010; Tarnocai et al, 2009). He et al.: Microbial decomposition model and boreal forest these models often predict a wide range of soil C response (Todd-Brown et al, 2013) and they omit key biogeochemical mechanisms based on empirical regression analyses (Conant et al, 2011; Schmidt et al, 2011). Recent mechanistically based models that explicitly account for microbial biomass pools and enzyme kinetics that catalyze soil C decomposition produce notably different results and provide a closer match to contemporary observations (Allison et al, 2010; Wieder et al, 2013)
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