Yafei Ding

The effect of afforestation in infertile mountainous areas is closely related to the soil ecological environment. Soil enzyme activities and the structure and functions of microbial communities are core indicators reflecting soil quality. Clarifying the response patterns of the two to Cyclobalanopsis gilva afforestation in infertile mountainous areas can provide a key scientific basis for targeted improvement of the cultivation efficiency of C. gilva plantations under different site conditions in the eastern subtropical region of China. In this study, 7-year-old C. gilva young forests in infertile mountainous areas and control woodland areas were selected in Shouchang Forest Farm, Jiande, Zhejiang Province, located in the subtropical region of China. Soil enzyme activities and microbial biomass in different soil layers, as well as metagenomes of rhizosphere and bulk soils, were determined to explore the effects and internal correlations of site conditions on soil enzyme activities and microbial community characteristics of C. gilva forests. The results showed that the activities of urease and catalase, as well as the content of microbial biomass nitrogen in the surface soil of infertile mountainous areas, were significantly lower than those in control woodland areas. The shared dominant phyla in the two types of sites included Proteobacteria and Acidobacteria, and the shared dominant genera included Bradyrhizobium. In addition, the relative abundances of three unclassified populations of Proteobacteria and functional genes related to cofactor and vitamin metabolism in the rhizosphere soil of infertile mountainous areas were significantly higher than those in control woodland areas. Meanwhile, the dominant microbial phyla in the rhizosphere soil of infertile mountainous areas had a closer correlation with soil enzyme activities and microbial biomass. This study clarified the ecological strategy of C. gilva young forests adapting to infertile mountainous areas: by increasing the relative abundances of functional genes related to cofactor and vitamin metabolism in rhizosphere microorganisms, promoting the enrichment of microorganisms associated with soil nitrogen cycling, and enhancing the correlations between dominant microbial phyla and soil enzyme activities and microbial biomass, the nitrogen resource limitation on soil microbial activity in infertile mountainous areas is balanced. This finding provides direct guidance for optimizing the afforestation and management techniques of C. gilva in infertile mountainous areas and has important practical value for promoting forest ecological restoration.

This study explores the effects of afforestation in infertile mountainous areas on soil microbial communities and functional nutrient cycling genes in young Cyclobalanopsis gilva forests, aiming to provide a scientific basis for promoting C. gilva growth. Employing metagenomic sequencing coupled with integrative analyses of microbial community structure and functional genes, this study took 7-year-old C. gilva forest stands in infertile mountainous areas of Shouchang Forest Farm, Zhejiang Province as the research object, using adjacent 7-year-old C. gilva forest in woodland areas as a control, to analyze the differences in soil microbial community structure and nutrient cycling functional genes in the rhizosphere (SCG) and non-rhizosphere (SNR) of infertile mountainous areas, as well as from the rhizosphere (FCG) and non-rhizosphere (FNR) of control woodland areas, and further explore their relationships with the growth of C. gilva. The results indicated that the contents of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and microbial biomass nitrogen (MBN) in SNR were significantly lower than those in FNR by 59.50%, 39.57%, 29.32%, and 53.13%, respectively. Bradyrhizobium and Trebonia were the dominant genera in both site conditions; however, the relative abundance of these genera was lower in infertile mountainous areas compared to the control. Notably, the Shannon and Simpson indices of SCG were significantly lower by 0.49 and 0.01 than those of SNR (p < 0.05), respectively. Additionally, the relative abundances of carbon fixation and nitrogen fixation of SCG were significantly higher than those of SNR. And the relative abundances of functional genes involved in carbon cycling (glyA, fdhA), nitrogen cycling (nasA, narfC, narC, and nirB), and phosphorus cycling (phoB) in infertile mountainous areas were significantly higher than those in the control. The nutrient cycling processes and the expression of functional genes in SCG are coordinately regulated by soil nutrients (SOC and TN) and microbial biomass [MBC (microbial biomass carbon) and MBN]. This work provides a mechanistic foundation for optimizing afforestation strategies and ecological restoration in nutrient-limited mountainous ecosystems, highlighting the critical role of microbial functional plasticity in overcoming edaphic constraints.