Responses of switchgrass soil respiration and its components to precipitation gradient in a mesocosm study

Aims: The objective of this study was to investigate the effects of the precipitation changes on soil, microbial and root respirations of switchgrass soils, and the relationships between soil respiration and plant growth, soil moisture and temperature. Methods: A mesocosm experiment was conducted with five precipitation treatments over two years in a greenhouse in Nashville, Tennessee. The treatments included ambient precipitation, −50%, −33%, +33% and +50% of ambient precipitation. Soil, microbial, and root respirations were quantified during the growing seasons. Results: Mean soil and root respirations in the +50% treatment were the highest (2.48 and 0.93 μmol CO₂ m⁻² s⁻¹, respectively) among all treatments. Soil microbial respiration contributed more to soil respiration, and had higher precipitation sensitivity mostly than root respiration. Increases in precipitation mostly enhanced microbial respiration while decreases in precipitation reduced both microbial and root respirations. Across precipitation treatments, soil respiration was significantly influenced by soil moisture, soil temperature, and aboveground biomass. Conclusions: Our results showed that microbial respiration was more sensitive to precipitation changes, and precipitation regulated the response of soil respiration to soil temperature. The information generated in this study will be useful for model simulation of soil respiration in switchgrass fields under precipitation changes.