Responses of Soil Respiration and Extracellular Enzyme Activities to Manipulated Precipitation Regimes in a Switchgrass Mesocosm Experiment
Precipitation regimes exert important controls on soil respiration but the underlying microbial mechanisms that likely mediate the effects remain rarely studied, particularly in a bioenergy cropland such as switchgrass (Panicum virgatum L.). In this study, a mesocosm experiment with five levels of precipitation representing ambient precipitation as a control (P0), two drought conditions (P-33 and P-50: 33% and 50% reduction relative to P0), and two wet conditions (P+33 and P+50: 33% and 50% enhancement relative to P0) was conducted to investigate the responses of switchgrass soil to altered precipitation regimes. Soil samples (0-15 cm) were collected in March 2017 and June 2019 and quantified for soil organic carbon (SOC), total nitrogen (TN), microbial biomass carbon (MBC), heterotrophic respiration (Rs), biomass specific respiration (Rss; respiration per unit of microbial biomass) and extracellular enzymes activities (EEAs). Results showed that changes in precipitation caused no significant effect on SOC and TN. Relative to P0, P+33 significantly increased Rs by 147.9% (P<0.05) and little changed MBC, leading to insignificant positive effects on Rss. Relative to P0, P+33 significantly increased hydrolytic carbon acquisition enzyme (C-acq) by 141.9% but did not significantly affect peroxidase (PEO). On the other hand, drought treatments (P-33 and P-50) led to numerical decreases in Rs. In addition, P-50 significantly suppressed MBC by 52.3% and P-33 significantly decreased PEO by 50.3%. N-acq was less sensitive to either increased or decreased precipitation. Relative to P0, P+50 and P+33 significantly increased aboveground biomass by 25% and 26.6%, respectively, and P-33 and P-50 significantly decreased aboveground biomass by 24.3% and 29.5%, respectively (P<0.05). Collectively, these results suggested that the enhanced quantity of precipitation stimulated soil respiratory C loss likely associated with increased aboveground biomass and elevated hydrolases. However, drought conditions had no significant impacts on respiratory carbon losses likely due to insignificant changes in enzyme activities or microbial physiology suggesting potential microbial tolerance to drought conditions in the switchgrass mesocosm experiment.
"Responses of Soil Respiration and Extracellular Enzyme Activities to Manipulated Precipitation Regimes in a Switchgrass Mesocosm Experiment"
ETD Collection for Tennessee State University.