Long-term vegetation succession enhances the network complexity and stability of soil protozoan communities

Abstract

Long-term vegetation succession is critical for the improvement of environmental quality and the restoration of ecosystem functions. As key links in the micro-food web, protozoa are widespread in the soil and are important participants in nutrient cycling and energy transfer. However, the effects of vegetation succession on soil protozoan communities compared to those on other soil microbial communities, such as bacteria and fungi, remain largely unknown. Here, a long-term vegetation succession sequence of approximately 160 years was selected to investigate the evolutionary characteristics and drivers of soil protozoan diversity, network stability, and community assembly processes. Soil protozoan alpha diversity increased significantly with vegetation succession, and beta diversity differed significantly between early and late successional stages. Microbial biomass is a key driver of soil protozoan diversity. In addition, the network robustness and complexity of soil protozoa increased significantly and stabilized during late successional stages. Soil microbes played a direct role in protozoan network stability, whereas abiotic factors played an indirect role, reflecting the trophic cascade in soil micro-food webs. The relative contributions of deterministic processes to the community assembly of soil protozoa increased progressively with vegetation succession, owing to multiple eco-selective mechanisms arising from environmental changes. Our results highlight the bottom-up effects of soil microbes on secondary consumer communities during natural restoration, providing new insights into the mechanisms underlying the maintenance of soil micro-food web diversity and stability across environmental gradients.