Ancient Walnut Trees in Periurban Areas Reduce Soil Microbial Network Complexity, Function, and Multifunctionality

Although extensive studies have explored the influence of stand age on soil microbial diversity and functionality; however, knowledge of ancient trees' impacts on soil microbial communities and multifunctionality is limited. Here, we analyzed the bacterial communities, keystone species, and potential functions associated with young (< 10 years), middle‐aged (about 50 years), and old (1000 years) trees of walnut ( Juglans regia L.) to track microbial‐mediated soil multifunctionality (SMF) on the Xizang Plateau. The SMF increased with the increase in stand age; however, old trees significantly reduced the SMF compared to middle‐aged trees. Old trees substantially decreased microbial diversity and reshaped the microbial community composition, decreasing the relative abundance of dominant bacterial taxa like Proteobacteria, Bacteroidota, and Gemmatimonadota. Metagenomic screening indicated that stand age brought about a concurrent reduction in the abundance of carbon (C)‐related genes, such as genes encoding glucoamylase, which breaks down starch, xylanase for hemicelluloses degradation, and endoglucanase for chitin degradation, as well as nitrogen (N)‐related genes, including amoA . Changes in the microbiota characteristics (diversity, composition, and network complexity) are strongly correlated with age‐induced changes in SMF. Our findings demonstrated that ancient trees in periurban areas have a notably negative effect on soil microbial communities and functionality. Thus, comprehending the intricacy of interactions between ancient trees and soil is crucial for formulating sustainable management and ancient tree conservation policies.