Disturbance intensity shapes the soil micro-food web compositions and energy fluxes during seven-year land use changes

Soil micro-food webs play an important role in ecosystem functions through energy flow; they are strongly influenced by land use types. Previous studies have typically utilized the space-for-time substitution or single-time sampling method to reflect the land-use change effects by comparing differences among existing land-use types. These methods would increase random error. Research on how synchronized land-use change (starting at the same time and place) influences soil ecological processes and functions is urgently needed. Based on a controlled field experiment and seven years of observations, this study explored the effects of land-use change from natural shrubland to cropland (maize), forage land (tall-grass forage), and economic forest land (walnut plantation) on the community structure and energy dynamics of the soil micro-food webs. Cropland simplified the complexity of the soil food webs compared to the other three land-uses. Forage grassland maintained the highest biomasses of soil total microbes, fungi, and arbuscular mycorrhizal fungi. In addition, economic forest land improved the flow uniformity of the micro-food web by increasing energy transfer from resources to bacterivores, fungivores, and herbivores while decreasing herbivore energy flow to omnivores-predators. Omnivore abundance and nematode diversity were important predictors of total energy flux and flow uniformity of the soil micro-food webs, respectively. In addition, omnivores maintained the complexity of soil micro-food webs by promoting interactions among trophic groups through top-down control. Soil organisms are sensitive to the response of agricultural management and planting time, and it may take several years or more to reach a dynamic equilibrium. Different types and levels of ecosystem disturbance (e.g., tillage and no-tillage, fertilizer rates, aboveground biomass removal intensity) may be the major drivers of soil community during land use change. Our findings highlight the importance of conservation agriculture in maintaining soil food web structure and energy flow for future sustainable land uses, and that promoting omnivore abundance is essential for food web complexity and stability.