Tree Species Mixing Regulates Soil Multi-Nutrient Cycling by Altering Microbial Network Complexity and Assembly Processes in Larix olgensis

TL;DR

Mixing tree species improves soil nutrient cycling by changing soil microbes and their interactions.

Contribution

The study reveals how tree species mixing affects soil microbes and nutrient cycling through microbial diversity and network changes.

Findings

Soil multi-nutrient cycling was significantly higher in mixed stands compared to pure stands.

Microbial diversity and network complexity were key predictors of improved nutrient cycling.

Bacterial assembly processes directly influenced soil nutrient cycling.

Abstract

Establishing mixed conifer–broadleaf forests enhances soil multi-nutrient cycling (SMC), yet the underlying mechanisms, particularly the role of rhizosphere microbial communities, remain poorly understood. This study investigated how bacterial and fungal communities in the rhizosphere soil of Larix olgensis drive SMC in both pure and mixed plantations with Fraxinus mandshurica, elucidating the microbial pathways for nutrient supply in mixed stands. Our results indicated that SMC in the L. olgensis rhizosphere soil was significantly greater in mixed stands (0.43) than in pure stands (−0.51). Tree species mixing significantly enhanced microbial diversity, increased the stochasticity of community assembly, and reduced dispersal limitation. Cross-kingdom (bacteria–fungi) co-occurrence networks in mixed stands showed a 19.7% increase in positive correlations, indicating stronger microbial cooperation. Random forest analysis identified microbial diversity, network complexity, and bacterial assembly processes as the main predictors of SMC. Structural equation modeling indicated that microbial diversity indirectly promoted SMC via increased network complexity, while bacterial assembly processes directly influenced SMC. These findings demonstrate that mixed conifer–broadleaf plantations improve soil microbial functioning and nutrient cycling by modifying microbial diversity, assembly processes, and interaction networks.

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