Conversion of pure Chinese fir plantation to multi-layered mixed plantation enhances the soil aggregate stability by regulating microbial communities in subtropical China

Soil aggregates are the basic units of soil structure, and their stability is a key indicator of soil quality and capacity to support ecosystem functions. The impacts of various environmental factors on soil aggregates have been widely studied. However, there remains elusive knowledge on the synergistic effects of changing forest stand structure on soil aggregate stability (SAS), particularly in subtropical China where soil erosion remains a critical issue. We investigated variations in the components of soil humus (HS), including humic acids (HAs), fulvic acids (FAs), and humins (HMs), under pure Chinese fir (Cunninghamia lanceolata) plantation (PP) and multi-layered mixed plantation (MP) comprising C. lanceolata, Castanopsis hystrix, and Michelia hedyosperma. The state of soil aggregate stability, was determined by three separate methods, i.e., dry-sieving, wet-sieving, and the Le Bissonnais. High-throughput sequencing was used to determine the diversity and composition of microbial communities under PP and MP. We then built partial least squares path models (PLS-PM) for assessing the responses of SAS to the variations in soil microorganisms and HS components. The MP stands had significantly greater SAS (P ​