Abstract:

Aims: Biodiversity loss and functional degradation caused by tropical land use change have attracted widespread attention. However, a systematic understanding of the response mechanisms, network topological adaptation strategies, and cross-trophic linkage dynamics of belowground multi-trophic soil micro-food webs (bacteria, fungi, protozoa, and nematodes) remains lacking. This study aimed to reveal the response patterns of each trophic level in belowground soil micro-food webs to intensive land use, their network structural reorganization strategies, and the underlying environmental driving mechanisms. 

Methods: In Xishuangbanna, four typical land use types representing an increasing gradient of disturbance (primary forest, secondary forest, open habitat, and rubber plantation) were selected. Based on 16S rRNA and 18S rRNA high-throughput sequencing technologies, community structures across four trophic levels were investigated, and a systemic study was conducted combining co-occurrence network analysis (evaluating complexity and modularity) with global Mantel tests. 

Results: (1) The micro-food web exhibited significant asynchronous responses, where bacterial diversity remained high in rubber plantations, whereas the diversity of higher-trophic protozoa decreased significantly with intensifying disturbance, and although nematode diversity remained stable, the omnivorous genus Oxydirus was not detected in secondary forest and rubber plantations. (2) Network reorganization strategies diverged, with lower trophic levels (bacteria and fungi) maintaining stability under intensifying disturbance by increasing modularity, whereas soil protozoa networks were markedly simplified (protozoan connections lost nearly 80%), and the nematode network in rubber plantations densified with connections becoming highly concentrated on a few nodes. (3) Environmental driving mechanisms underwent severe decoupling, where micro-food web assembly in primary forests was dominated by soil physical structure (particle size distribution and porosity), but with the degradation of soil physical conditions in rubber plantations (clay loss and total porosity decline), the assembly of higher-trophic communities became significantly decoupled from environmental factors, shifting the dominant driving force from deterministic environmental filtering to ecological drift. 

Conclusion: This study emphasizes that the degradation of soil physical microhabitats is the key factor triggering the simplification of higher-trophic networks, indicates the limitations of relying solely on microorganisms to assess ecosystem health, and provides a scientific basis for ecological restoration and multi-trophic biodiversity conservation in tropical plantations.

Key words: land use change, soil micro-food web, network analysis, asynchronous response, rubber plantations, Xishuangbanna, multi-trophic levels