Abstract
The relationship between microbial respiration rate and soil moisture content is an important property for understanding and predicting soil organic carbon degradation, CO2 production and emission, and their subsequent effects on climate change. This paper reports a pore-scale modeling study to investigate the response of heterotrophic respiration to moisture conditions in soils and to evaluate various factors that affect this response. X-ray computed tomography was used to derive soil pore structures, which were then used for pore-scale model investigation. The pore-scale results were then averaged to calculate the effective respiration rates as a function of water content in soils. The calculated effective respiration rate first increases and then decreases with increasing soil water content, showing a maximum respiration rate at water saturation degree of 0.75, which is consistent with field and laboratory observations. The relationship between the respiration rate and moisture content is affected by various factors, including pore-scale organic carbon bioavailability, the rate of oxygen delivery, soil pore structure and physical heterogeneity, soil clay content, and microbial drought resistivity. Overall, this study provides mechanistic insights into the soil respiration response to the change in moisture conditions, and reveals a complex relationship between heterotrophic microbial respiration rate and moisture content in soils that is affected by various hydrological, geophysical, and biochemical factors.
Highlights
Moisture is one of the most important environmental factors influencing heterotrophic respiration (HR) in soils (Bond-Lamberty and Thomson 2010; Falloon et al 2011; Moyano et al 2013; Orchard and Cook 1983; Sierra et al 2015)
This literature reported the responses of soil respiration rate to
From the pore-scale point of view, the increase in HR rate with increasing saturation degree when S is below Sop is because the local mass transfer rate of soil organic carbon from sorbed to dissolved phases increases with moisture content (Eq 13), which subsequently increases the pore-scale concentration of dissolved organic carbon and the rate of carbon degradation (Eq 1)
Summary
Moisture is one of the most important environmental factors influencing heterotrophic respiration (HR) in soils (Bond-Lamberty and Thomson 2010; Falloon et al 2011; Moyano et al 2013; Orchard and Cook 1983; Sierra et al 2015) It affects soil organic carbon (SOC) bioavailability and the rate of oxygen delivery that affect microbial metabolism in regulating heterotrophic SOC decomposition (Moyano et al 2012; Rodrıguez-Iturbe and Porporato 2005). Reactive transport processes including moisture-dependent diffusion for describing substrate transport and Michaelis–Menten kinetics for describing microbial respiration have been considered in the process-based models (Davidson et al 2012) By incorporating these processes the models provide important insights into the relationship between the HR rate and moisture content (Moyano et al 2012, 2013). Pore-scale investigation on the effects of soil heterogeneity, SOC bioavailability, moisture content distribution, and substrate transport on soil respiration rates have not been investigated
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