Soil microbial respiration adapts to ambient temperature in global drylands.

Heterotrophic soil microbial respiration-one of the main processes of carbon loss from the soil to the atmosphere-is sensitive to temperature in the short term. However, how this sensitivity is affected by long-term thermal regimes is uncertain. There is an expectation that soil microbial respiration rates adapt to the ambient thermal regime, but whether this adaptation magnifies or reduces respiration sensitivities to temperature fluctuations remains unresolved. This gap in understanding is particularly pronounced for drylands because most studies conducted so far have focused on mesic systems. Here, we conduct an incubation study using soil samples from 110 global drylands encompassing a wide gradient in mean annual temperature. We test how mean annual temperature affects soil respiration rates at three assay temperatures while controlling for substrate depletion and microbial biomass. Estimated soil respiration rates at the mean microbial biomass were lower in sites with higher mean annual temperatures across the three assayed temperatures. The patterns observed are consistent with expected evolutionary trade-offs in the structure and function of enzymes under different thermal regimes. Therefore, our results suggest that soil microbial respiration adapts to the ambient thermal regime in global drylands.