干旱区生态环境知识资源中心

[1] Predicted precipitation regime changes in ari d 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.