Forest conversion can cause drastic changes in soil organic carbon (SOC) and soil microbial community (SMC), which is particularly evident in rhizosphere because it is a microbial hotspot with high microbial abundance and high-quality substrate input. However, the relationship between SMC structure in rhizosphere soil and carbon stability under long-term forest conversion remains unclear. 

The Global Change Ecology Group in Wuhan Botanical Garden (CAS) has constructed a 36-year forest conversion scenario in subtropical region of China, and examined SOC stability (expressed by aggregate fractionation) and the SMC structures in bulk and rhizosphere soils. The relationships of SOC with SMC structures in bulk and rhizosphere soils were compared.  

Results revealed that under the long-term forest conversion, SMC structure in rhizosphere soil evidently differentiated from that in bulk soil and was distinctly species-specific, representing more sensitivity to forest conversion. Dissolved organic nitrogen (DON) and pH were the primary determinants of SMC structure differentiation, of which gram-negative bacteria (GN) and fungi are the dominant groups.     

As bulk-SOC contents in the converted plantations restored to native status in the previous natural forest, the aggregate-SOC contents tended to stabilize, reflected by the lower SOC content in aggregates of <53 μm (F53-SOC) –in natural forest than in all the plantations, implying growing SOC sequestration potential in surface soil. Furthermore, SMC structure in rhizosphere soil is positively correlated with the F53–SOC content.   

The study found that, relative to that in bulk soil, SMC structure in rhizosphere soil can be more indicative of the dynamics of aggregate-SOC in response to the forest conversion, which will be helpful for further understanding of soil carbon process in response to land-use change in subtropical forests.  

This work was supported by the Natural Science Foundation of China, which has been published in Rhizosphere entitled “Microbial community structure in rhizosphere soil rather than that in bulk soil characterizes aggregate-associated organic carbon under long-term forest conversion in subtropical region”.