Root litter inputs exert greater influence over soil C than does aboveground litter in a subtropical natural forest

Aims: Changes in plant net primary production due to climate change can influence aboveground and belowground litter inputs to forest soils. We aim to examine the effects of such changes on soil carbon in subtropical forest ecosystems where these effects have not been thoroughly investigated. Methods: We manipulated aboveground litter inputs and excluded roots in a factorial design, and measured the effects of each treatment and their interactions on soil carbon (C) and soil microbial community structure. Results: After only 3 years of treatment, aboveground litter addition and root exclusion respectively caused 9% and 21% reductions in soil C concentration in the 0–10 cm soil, likely through different mechanisms. The reduction of soil C with aboveground litter addition was attributed to a priming effect, while reduced root-derived C inputs were likely the cause of the C reduction associated with root exclusion. PLFA analysis showed that both aboveground and belowground litter manipulations reduced Gram-positive bacteria biomass (by 30%–58%) compare to the control, but only root exclusion significantly reduced the actinobacteria biomarkers (by 46%–58%). Fungi, arbuscular mycorrhizal fungi, and ratios of Gram-negative to Gram-positive bacteria and bacteria to fungi did not differ among treatments. Conclusion: Our results show that root-derived C inputs exert a stronger control on soil C concentrations and microbial community structures than aboveground litter does in subtropical natural forest soils. Our study also highlights that that both increases in aboveground litter and decreases in belowground C input to soil can lead to reduced soil C.