Intercropping improves the complexity of cross-kingdom networks between bacterial and fungal communities associated with soil carbon cycling in Hainan island of China

Black pepper (Piper nigrum L.) intercropped with areca palm (Areca catechu L.) represents the main composite planting pattern for black pepper production in Hainan Province, China. This intercropping system can enhance black pepper yield by altering soil physicochemical properties and microbial communities. However, the mechanisms by which microorganisms influence soil nutrient cycling and the changes in soil microbial communities—particularly cross-kingdom networks linking bacteria and fungi—remain largely unknown. Here, we comprehensively examined soil physicochemical properties, enzyme activities, microbial communities, and cross-kingdom networks of bacteria and fungi. Intercropping strengthened the relationships between soil nutrients and enzyme activities and promoted soil carbon cycling by increasing β-glucosidase activity, primarily driven by bacterial functions in carbon metabolism. Bacterial diversity responded more strongly to intercropping than fungal diversity. Moreover, this practice substantially increased the complexity of microbial co-occurrence networks in both bacterial and fungal communities. Intercropping also enhanced the interconnections between abiotic and biotic factors, particularly increasing the complexity and stability of cross-kingdom microbial networks.