Reductions in daily soil temperature variability increase soil microbial biomass C and decrease soil N availability in the C hihuahuan Desert: potential implications for ecosystem C and N fluxes

Maximum and minimum soil temperatures affect belowground processes. In the past 50 years in arid regions, measured reductions in the daily temperature range of air ( DTR air ) most likely generated similar reductions in the unmeasured daily temperature range of soil ( DTR soil ). However, the role of DTR soil in regulating microbial and plant processes has not been well described. We experimentally reduced DTR soil in the C hihuahuan Desert at Big Bend National Park over 3 years. We used shade cloth that effectively decreased DTR soil by decreasing daily maximum temperature and increasing nighttime minimum temperature. A reduction in DTR soil generated on average a twofold increase in soil microbial biomass carbon, a 42% increase in soil CO 2 efflux and a 16% reduction in soil NO 3 − –N availability; soil available NH 4 + –N was reduced by 18% in the third year only. Reductions in DTR soil increased soil moisture up to 15% a few days after a substantial rainfall. Increased soil moisture contributed to higher soil CO 2 efflux, but not microbial biomass carbon, which was significantly correlated with DTR soil . Net photosynthetic rates at saturating light ( A sat ) in L arrea tridentata were not affected by reductions in DTR soil over the 3 year period. Arid ecosystems may become greater sources of C to the atmosphere with reduced DTR soil , resulting in a positive feedback to rising global temperatures, if increased C loss is not eventually balanced by increased C uptake. Ultimately, ecosystem models of N and C fluxes will need to account for these temperature‐driven processes.