Linking microbial community structure to carbon substrate chemistry in soils following aboveground and belowground litter additions

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Plant aboveground litter (AL) and belowground litter (BL) differ in their carbon (C) chemistry, which can substantially affect soil microbial communities through litter inputs. Few studies, however, have compared how AL and BL additions to the soil change C substrate chemistry, microbial communities and their relationships during various decomposition stages. We tracked concurrent changes in C substrate chemistry and microbial communities with AL and BL addition to bare soil based on a 412-day laboratory incubation experiment. Carbon substrate chemistry was measured by solid-state 13C nuclear magnetic resonance (NMR), and the microbial community was measured by quantitative real-time polymerase chain reaction (qPCR) and high-throughput sequencing. We found that AL addition strongly increased the gene copy number of both bacterial and fungal communities in the early stage of decomposition (the first 72 days) but had no effect on their gene copy number in the late stage of decomposition (after 72 days). The bacterial community composition in bare soil and soil with AL addition diverged, while the fungal community composition converged from the early to the late stage. BL addition, in contrast, did not strongly change the gene copy number or composition of bacterial and fungal communities in either the early or late stages. Labile C (e.g., O-alkyl-C), whose content increased significantly with AL addition but not with BL addition, was the key C substrate affecting microbial communities throughout the whole incubation period. Our findings demonstrate that the effects of labile C on soil decomposition can persist for a long time. The responses of bacterial and fungal communities to labile C inputs differ in various decomposition stages, which is important for predicting soil and litter decomposition processes, and thereby soil carbon sequestration.