Tree species influence microbiome-mediated nutrient sequestration in soil aggregates of subtropical plantations in China

Abstract

The mixed planting of tree species regulates nutrient and carbon cycling in forest ecosystems by shaping soil microbial communities. However, the mechanisms by which tree species identity regulates microorganism-driven nutrient cycling within soil aggregates remain elusive. This study investigated how tree species identity shapes soil aggregate microorganisms and functions related to nutrient cycling in five mixed plantations, established by introducing broadleaved trees (Camellia oleifera Abel, Manglietia chingii Dandy, Cercidiphyllum japonicum Sieb. et Zucc., Michelia maudiae Dunn, and Bretschneidera sinensis Hemsl.) into subtropical coniferous monocultures (Pinus massoniana Lamb.) after thinning. We found that mixing tree species induced shifts in microbial communities, particularly within <2 mm aggregates, where diversity increased compared to monocultures. This was primarily driven by the heterogeneous nutritional resources and microenvironments created by mixed plantations. Notably, the abundance of Actinobacteria and Basidiomycota increased, indicating a transition towards nutrient-rich microenvironments and enhanced organic matter degradation. While mixed plantations fortified fungal network stability, the impact on bacterial networks varied with tree species characteristics, suggesting fungi are more responsive to nutrient differences caused by tree diversity. Furthermore, litter quality (carbon and nitrogen concentration), enzyme activities [(l-leucine aminopeptidase + β-1,4-N-acetylglucoaminosidase)/acid phosphatase], and bacterial Shannon index emerged as key drivers of carbon, nitrogen, and phosphorus accumulation in aggregates. Therefore, our findings underscore that tree species identities influence the interactions between microorganisms and nutrients within aggregates, enhancing nutrient retention and contributing to soil ecosystem multifunctionality and stability. Thus, optimizing tree species composition in plantations can enhance soil fertility and support adaptive forest management.