Abstract
Soil microbial respiration is one of the largest sources of carbon (C) emissions to the atmosphere in terrestrial ecosystems, which is strongly dependent on multiple environmental variables including soil moisture. Soil moisture content is strongly dependent on soil texture, and the combined effects of texture and moisture on microbial respiration are complex and less explored. Therefore, this study examines the effects of soil moisture on the mineralization of soil organic C Soil organic carbon in three different soils, Ultisol, Alfisol and Vertisol, collected from mixed forests of Georgia, Missouri, and Texas, United States , respectively. A laboratory microcosm experiment was conducted for 90 days under different moisture regimes. Soil respiration was measured weekly, and destructive harvests were conducted at 1, 15, 60, and 90 days after incubation to determine extractable organic C (EOC), phospholipid fatty acid based microbial community, and C-acquiring hydrolytic extracellular enzyme activities (EEA). The highest cumulative respiration in Ultisol was observed at 50% water holding capacity (WHC), in Alfisol at 100% water holding capacity, and in Vertisol at 175% WHC. The trends in Extractable Organic Carbon were opposite to that of cumulative microbial respiration as the moisture levels showing the highest respiration showed the lowest EOC concentration in all soil types. Also, extracellular enzyme activities increased with increase in soil moisture in all soils, however, respiration and EEA showed a decoupled relationship in Ultisol and Alfisol soils. Soil moisture differences did not influence microbial community composition.
Highlights
Soil organic carbon (SOC) is the largest and most dynamic terrestrial C reserve (Jobbágy and Jackson, 2000) and understanding SOC decomposition in response to environmental changes is critical for predicting CO2 feedbacks driving future climates (Davidson and Janssens, 2006; Schmidt et al, 2011; Hao et al, 2017; Su et al, 2020)
The finding that microbial respiration is changing with soil moisture content, microbial community is not, probably implying microbial acclimation to varying moisture regimes. These results showed that short-term laboratory incubations at different soil moisture levels did not change microbial community composition, microbial activity was affected as indicated by changes in extractable organic C (EOC), C acquiring enzyme activities and CO2 fluxes
Understanding the dependency of microbial respiration on soil moisture and soil texture is important for reducing the uncertainty in modeling SOC dynamics under changing climate
Summary
Soil organic carbon (SOC) is the largest and most dynamic terrestrial C reserve (Jobbágy and Jackson, 2000) and understanding SOC decomposition in response to environmental changes is critical for predicting CO2 feedbacks driving future climates (Davidson and Janssens, 2006; Schmidt et al, 2011; Hao et al, 2017; Su et al, 2020). The existing literature shows that the soil moisture-respiration relationship is complex and site-specific, and is strongly controlled by porosity, bulk density, texture, and SOC concentration (Franzluebbers, 1999; Thomsen et al, 1999; Moyano et al, 2012; Herbst et al, 2016; Homyak et al, 2018; Li et al, 2020). Soil C models tend to rely on empirical soil moisturerespiration functions which are developed and validated based on site-specific studies (Bauer et al, 2008; Falloon et al, 2011) These functions represent an average response of the moisture-respiration relationships, can introduce uncertainties into predictions of the SOC budget (Sierra et al, 2015)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call