Effects of labile carbon addition on organic carbon mineralization and microbial growth strategies in subtropical forest soils.

Abstract

Deep soil is a major organic carbon pool in terrestrial ecosystems. Labile carbon inputs can stimulate soil organic carbon (SOC) mineralization, causing priming effect, which in turn affects soil carbon emission. However, the mechanism of the priming effect in deep soil is still unclear. Therefore, to know how deep soil responds to labile carbon addition is essential for better understanding of deep soil carbon dynamics. In this study, we incubated three profiled soils (0-10 cm, 10-30 cm, 30-60 cm) from a subtropical forest with 13C-labeled glucose addition to analyze the priming effects and their relationship with the shift of microbial communities (r-K strategies). The results showed that glucose addition increased SOC mineralization in all soil layers, causing positive priming effects. But glucose addition significantly decreased the specific growth rates of microorgani-sms for all soils, indicating a relative decrease of r-strategists and a relative increase of K-strategists in the microbial community. Thus, we inferred that the positive priming effect was possibly attributed to the increased contribution of K-strategists. The priming effect in deep soil (156%) was significantly higher than that in surface soil (45%). Meanwhile, the ratio of dissolved organic carbon (DOC) and dissolved nitrogen (DN) after glucose addition was significantly higher in deep soil (76.03) than that in surface soil (13.00). These results suggested that there existed a stronger nitrogen limitation in deep soil. The microorganisms in deep soil tended to decompose recalcitrant SOC to acquire nitrogen, which then caused a greater priming effect. Overall, deep soil was more vulne-rable to labile carbon addition due to its carbon and nitrogen limitations, and hence was likely more sensitive to climate change in the future.