The influence of rewetting intensity on soil priming after drought

Abstract

Soil moisture is a key driver of soil organic matter (SOM) decomposition and the global carbon (C) cycle, and climate warming-induced extremes of rainfall and drought are intensifying the dynamics of soil C stocks. Although addition of labile C pools can trigger strong priming effects (PE) by stimulating decomposition of recalcitrant SOM, how varying rewetting intensity interacts with these exogenous inputs of C pools to affect PE remains unclear. In this study, we used an isotopic approach to examine the effects of rewetting intensity (40%, 60%, and 80% water holding capacity (WHC)) on PE during a 21-day incubation following intensive drought (20% WHC). Our results show that glucose addition induced a strong positive PE, with higher moisture (60% and 80% WHC) resulting in greater PEs. High moisture regulated microbial community composition and boosted microbial activity and turnover. These changes heightened microbial nitrogen demand, accelerated nitrogen mining, and intensified decomposition of stable C, leading to net soil-C loss. The correlation analysis shows that enhanced biosynthetic and degradative activity under higher moisture conditions facilitates the turnover of labile C, whereas reduced microbial diversity and metabolic intensity promote the stabilization of more persistent C forms. This study underscores the significant role of moisture in shaping PEs and soil C dynamics in the subtropical forest soils, offering insights into soil C sequestration in response to climate change.