The formation and subsequent sequestration of soil organic carbon(SOC) during forest succession are primarily driven by soil microorganisms. The microbial residues are important source of soil organic C and play an important role in C sequestration by soil. Amino sugars are biomarker of microbial residues. 

The subtropical forest succession include three stages: early coniferous forest, middle mixed species forest and climax broad-leaved forest. In the process, litter quality affects the substrate use efficiency and community composition of microbes. However, the long-term associations between soil organic C accumulation and the functions of soil microbes in C sequestration are still unknown. 

The Research Group of Matter Cycling Process from Institute of Applied Ecology (IAE) of the Chinese Academy of Sciences investigated the subject by determination of the changes of amino acid content and its ratio to the whole amount of organic carbon along soil profiles, and then they assessed the role of microbes in the process of soil carbon accumulation. 

The results show that in the profile from 0 to 40 cm, the whole organic C content and amino sugar content both gradually increased with the succession process, indicating that the C sequestration by soil is closely associated with the process of microbial proliferation and death.  

Litters of coniferous trees are relatively hard to decompose so that the contribution of microbial residues to the soil C accumulation is relatively low. The invade of broad-leaved trees in the forest increased the accumulation of microbial residues and C sequestration by soil.

However, from early to middle stages of succession, the accumulation of amino sugar was faster than soil organic C. This may implicate that the formation and accumulation of microbial residues is the prerequisite of organic C sequestration. 

The structure of fungal residues makes them more difficult to decompose than bacteria. In the middle successional stage, the ratio of fungal residues to the whole organic C is highest, but in the climax stage the bacterial residues were more easily accumulated.

So, during the process of subtropical forest succession, the soil organic C accumulation may pass the stage of fixation by fungal residues and then gradually transited to the stage of accumulation of bacterial residues. 

Dinghushan forest ecosystem is dominated by middle staged coniferous- broad leaved trees mixed forest, so it is suggested the forest soil still has considerable ability in carbon sequestration. 

The work is the first time to recover that microbes affect changes in chemical composition of organic matter. This helps understanding on the long-term changes in soil carbon dynamics.  

The results were published in a top journal of soil science Soil Biology and Biochemistry entitled "Linkage of microbial residue dynamics with soil organic carbon accumulation during subtropical forest succession".

Thi work was supported by special project in CAS Strategic Pilot Program, NNSFC, National Key R & D Project and CAS innovation group Project.