Effects of changing precipitation regimes on dryland soil respiration and C pool dynamics at rainfall event, seasonal and interannual scales

Predicted precipitation regime changes in arid ecosystems have the potential to alter soil C balance, but the influence of changes in different aspects of precipitation (amount, seasonality, and intensity) and the factors contributing to such effects are poorly understood. We used a process‐based ecosystem model (PALS) that was modified, parameterized, and evaluated for a Mojave Desert ecosystem in the southwestern US to simulate how dryland soil respiration (R s ) and soil C pool size responded to precipitation changes at multiple temporal scales. The effects of changing precipitation on R s were largely mediated by the contrasting respiratory response of plants (R a ) and soil microbes (R h ) and confounded by predrought duration, season, soil temperature, plant phenology, and substrate availability. Increases in precipitation amount stimulated R s and increased the contribution of R a to R s , whereas reductions in summer rainfall and strong increases in rainfall event size reduced total R s and decreased the contribution of R a to R s . Increases in annual rainfall and decreases in summer rainfall benefited dryland soil C sequestration, whereas strong increases in rainfall event size resulted in a loss of soil C, with labile soil C pools being more responsive to precipitation regime changes than recalcitrant C pools at a decadal scale. These simulation results implied that dryland soils may act as C sinks with increased precipitation amount or C sources with decreased precipitation amount, but the strength of the sink/source may be mediated by accompanying shifts in rainfall seasonality and event size distribution.