Long-term experimental warming decreased labile soil organic carbon in a tallgrass prairie

Aims: Climate warming has been hypothesized to influence dynamics of soil organic carbon (SOC), especially labile SOC due to its rapid response to changes in temperature and carbon (C) supply. In this study, we examined impacts of experimental warming on the labile and whole SOC pools in association with warming-induced vegetation changes from 2000 to 2008 in a tallgrass prairie in Oklahoma, USA. Methods: Infrared heaters were used to elevate soil temperature by approximately 2°C since November 1999. The modified potassium permanganate (KMnO₄, 0. 02 mol L^-1) procedure was used to estimate chemically labile organic C (LOC). Results: Warming significantly decreased chemically labile organic C (LOC) by an average of 15. 56 %, but had little effect on SOC content. The decrease in LOC was probably attributable to increased soil respiration, enhanced soil erosion, and possibly stimulated C₄ dominance under warming. Warming did not induce an instantaneous decrease in LOC. A 2-stage variation in LOC response to warming was observed, with no significant changes from 2000 to 2004 and significant decreases from 2005 to 2008. Lagged temporal dynamics of LOC (2 yrs) asynchronously correlated with warming-increased C₄ proportion of aboveground biomass (AGB). Conclusions: Our findings suggest that staged decrease in LOC under warming may potentially relate to the increase in C₄ biomass through detrital inputs, making it complex to predict the effect of warming on C cycling in this region.