Experimental warming reduced topsoil carbon content and increased soil bacterial diversity in a subtropical planted forest

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200206853

The potential effects of global warming on the soil carbon (C) dynamics of subtropical forests are still uncertain. To assess the effects of warming on soil C and tree roots, combined soil warming (infrared heaters, +1.5 °C soil temperature) and trenching experiments were conducted in a subtropical Castanopsis hystrix plantation. Topsoil C content was reassessed after five years of warming, and the effects on soil organic carbon (SOC) quality and microbial diversity were analyzed. Compared with corresponding controls, the topsoil (0–10 cm) SOC content was significantly lower in un-trenched warmed soil (-13.6%) as well as in trenched warmed soil (-15.4%). However, the range of SOC content after five years of warming was similar to that observed after two years of warming
(-14.6%, -19.2%), indicating that the warming effect on SOC content leveled off during the latter three years. In trenched plots, warming significantly decreased the carbohydrate C as well as the ratio of carbohydrate C to N-alkyl/methoxyl C ratio, suggesting that labile C was preferentially decomposed. In un-trenched plots, SOC quality was unaffected, indicating a compensatory input of labile root C. Bacterial α-diversity increased under warming, whereas no significant warming effects on fungal community diversity were observed. Both the SOC content and the proportion of soil carbohydrate C were negatively correlated with soil bacterial α-diversity, suggesting that the abundance of more recalcitrant SOC increased soil microbial diversity. Overall, soil warming resulted in a reduction
in SOC in the first two years, and then SOC content was sustained.