Pore-scale investigation on the response of heterotrophic respiration to moisture conditions in heterogeneous soils

Abstract

The relationship between microbial respiration rate and soil moisture content is an important property for understanding and predicting soil organic carbon degradation, CO 2 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 porescale 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.

Distinct Source Water Chemistry Shapes Contrasting Concentration‐Discharge Patterns

“…Here we take a commonly used median value of 2.0. The f ( S w ) takes the form of f ( S w ) = ( S w ) n , where n is the exponent reflecting effects of soil water content on reaction (Yan et al, ); a value of n = 2 is considered applicable for most soil textures (Hamamoto et al, ).…”

Coupling between the terrestrial carbon and water cycles—a review

“…sap conductivity) at the expense of safety (i.e. resistance to drought) Soil moisture is also an important regulator of heterotrophic respiration (Manzoni et al 2012, Suseela et al 2012, Ryan et al 2015, Yan et al 2016, Zhang et al 2018a, which represents about half of the total CO 2 emissions from soils. Low soil moisture conditions limit heterotrophic respiration rates through the reduction of solute transport and can trigger microbial dormancy in extreme drought conditions (Manzoni et al 2012, Suseela et al 2012, Ryan et al 2015, Yan et al 2016, Zhang et al 2018a.…”

CO<sub>2</sub> efflux from soils with seasonal water repellency

“…Soil moisture is one of the most important environmental factors regulating the production and transport of CO 2 in terrestrial ecosystems (Maier et al, 2011;Moyano et al, 2012). It influences not only soil organic C bioavailability and regulates access to oxygen (O 2 ) (Moyano et al, 2012;Yan et al, 2016) but also C mass transport (Davidson et al, 2012).…”

“…4782 E. Urbanek and S. H. Doerr: CO 2 efflux from water repellent soils Soil C models consider changes in soil moisture conditions, but they use functions that represent a response of soil respiration (i.e. CO 2 efflux) to average soil water content (SWC) and do not account for within-soil moisture variability, which is a characteristic of most soils (Rodrigo et al, 1997;Moyano et al, 2013;Yan et al, 2016). Most soils are very heterogeneous, with moisture distribution and water movement being variable and dependent on a number of factors (e.g.…”