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

[1] 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 (Rs) and soil C pool size responded to precipitation changes at multiple temporal scales. The effects of changing precipitation on Rs were largely mediated by the contrasting respiratory response of plants (Ra) and soil microbes (Rh) and confounded by predrought duration, season, soil temperature, plant phenology, and substrate availability. Increases in precipitation amount stimulated Rs and increased the contribution of Ra to Rs, whereas reductions in summer rainfall and strong increases in rainfall event size reduced total Rs and decreased the contribution of Ra to Rs. 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.