AGE-RELATED CHANGES IN SOIL AND MICROBIAL C:N:P STOICHIOMETRY IN ZENIA INSIGNIS PLANTATIONS IN KARST REGIONS OF SOUTHWEST CHINA

Afforestation is a key strategy for vegetation restoration in the karst rocky desertification regions of southern China. Zenia insignis is widely cultivated for this purpose. However, there is a scarcity of data on soil nutrient status and biogeochemical cycles concerning different stand ages in Z. insignis plantations within these ecosystems. This study assessed the concentrations of carbon (C), nitrogen (N), and phosphorus (P) and their stoichiometric ratios in soil and microbial biomass across Z. insignis plantations of varying ages (3-5, 9-11, 14-16, 19-21, and 24-26 years) in the karst region of Guangxi Province, Southwest China. The results showed that soil C, N, and P concentrations increased with stand age, with significant differences in C content among different ages. Notably, the C:P ratio varied significantly between stands aged 3-5 years and those aged 19-26 years, as did the N:P ratio between stands aged 3-11 years and those aged 24-26 years. The concentrations of soil microbial biomass C (SMBC), microbial biomass N (SMBN), and microbial biomass P (SMBP) also tended to increase with stand age. Differences were observed between stands aged 3-5 years and those aged 24-26 years for SMBC, SMBN, and SMBP but not for the microbial C:N:P ratio. Our study revealed no significant associations between soil and microbial stoichiometric ratios. However, significant correlations were found between SMBC:SMBP and SMBC:SMBN, as well as between SMBN:SMBP. This study underscores the complex responses of soil and microbial stoichiometry to age variations in Z. insignis in the karst desertification of Southwest China.