Tracking C and N flows through microbial biomass with increased soil moisture variability

► Microbial sensitivity to moisture variability increases with grassland MAP. ► Microbial communities in mesic grassland soils utilized N-free protective solutes. ► Upon osmotic downshock microbes rapidly catabolized protective solutes. ► High moisture variability led to temporal decoupling of nitrification and denitrification. ► Protective solutes represent a significant proportion of total C and N cycling.