Changing characteristics and influencing factors of the soil microbial community during litter decomposition in a mixed Quercus acutissima Carruth. and Robinia pseudoacacia L. forest in Northern China

Abstract Soil microorganisms play an important role in the decomposition of litter. There stand structure and in-forest microenvironment of mixed forests and pure forests are different, and whether these differences affect the soil microbial community structure and further affect litter decomposition needs further research. In this paper, a mixed Quercus acutissima Carruth. and Robinia pseudoacacia L. (QR) forest and a pure Quercus acutissima Carruth. (QAC) forest were studied to analyse the compositions and influencing factors of soil bacterial and fungal communities during litter decomposition. Through field sampling and quantitative analysis performed in a laboratory, the results of this research were as follows: (1) During litter decomposition, the litter decomposition rate of the QR forest was higher than that of the QAC forest. (2) The dominant bacteria were Acidobacteria, Proteobacteria and Actinobacteria, and the dominant fungi were Basidiomycota and Ascomycota in the QR and QAC forests. (3) For litters decomposed from May to November, the soil bacterial alpha diversity index (richness index and evenness index) showed an increasing trend and the soil fungal alpha diversity index showed a decreasing trend in the QR and QAC forests, but the changes in the QR forest were smaller than those in the QAC forest. (4) Redundancy analysis (RDA) showed that the soil bacterial community structure was different between the QR and QAC forests, and the soil temperature, soil moisture, litter TN, C:N ratio, and N:P ratio were important factors affecting the soil microbial community structure. The results indicate that mixed forests have a more stable microbial alpha diversity index and that the TN, C:N ratio and N:P ratio of litter have important effects on soil microbial community structure; therefore, mixed forests should be given more priority in ecological restoration, and nitrogen regulation must be given attention during forest management.