Microbial responses to temperature sensitivity of soil respiration in a dry fallow cover cropping and submerged rice mono-cropping system

Soil heterotrophic respiration (SHR) increases exponentially with temperature and this general information has been incorporated into soil carbon models. However, the positive feedback of warming to SHR remains uncertain, mostly due to the differential response of soil microbial community to warming under dry and flooded conditions in a rice mono-cropping system. In this study, we aimed to evaluate the relationship between SHR and microbial functional groups during the fallow and flooded rice cultivation seasons under changing temperature in a rice mono-cropping system. Field experiments were conducted to investigate SHR, soil microbial functional groups and biomass, and temperature sensitivity of SHR (Q10) under dry fallow conditions during the cover cropping season and under flooded conditions during the rice cropping season. We found that SHR increased with increasing air and soil temperature, carbon availability, and soil microbial community composition and biomass in the fallow season, whereas a decrease in SHR in spite of an increase in temperature and carbon availability was observed under flooded conditions during the rice cropping season. Furthermore, a nonlinear response of microbial community composition and biomass with SHR was noticed during the flooded rice cropping season. This suggests that flooding could be the limiting factor for temperature sensitivity of SHR as well as microbial community composition in a rice mono-cropping system. Flooding the soil significantly (p < 0.01) decreased Q10. We therefore conclude that temperature, moisture region and carbon availability, rather than only soil microbial community composition are responsible for the spatiotemporal variation in SHR in a rice mono-cropping system in this region.