The relative controls of temperature, soil moisture, and plant functional group on soil CO 2 efflux at diel, seasonal, and annual scales

Soil respiration ( R soil ) is a dominant, but variable, contributor to ecosystem CO 2 efflux. Understanding how variations in major environmental drivers, like temperature and available moisture, might regulate R soil has become extremely relevant. Plant functional‐type diversity makes such assessments difficult because of the confounding influence of varied plant phenology and influences on soil microhabitats. We used automated measurement systems to quantify R soil in the three microhabitats (under mesquites, under bunchgrasses, and in intercanopy soils) that result from mesquite encroachment into grasslands to inform our understanding of diel R soil patterns in response to changes in temperature, seasonal variations in R soil in response to varied soil moisture and plant phenology, and the contribution of each microhabitat to total ecosystem‐scale R soil . We detected a counterclockwise hysteretic response of R soil to soil temperature, such that up to 100% greater fluxes were observed in the afternoon/evening than the morning for the same temperature. Phenological differences influenced ecosystem‐scale R soil in that mesquites were physiologically active months before bunchgrasses and R soil rates under mesquites were greater and elevated longer in response to rains. Cumulative annual R soil was 412, 229, and 202 g C m −2 under mesquites, bunchgrasses, and intercanopy spaces, respectively. Extrapolating to the ecosystem‐scale using cover estimates within the site's eddy covariance footprint illustrated that average mesquite R soil contributed 46% to overall ecosystem‐scale R soil , though mesquite composed only about 35% of the site. As grasslands transition to shrub dominance, the contribution of R soil to net ecosystem flux will likely increase, potentially offsetting presumed greater CO 2 uptake potential of woody plants.