Vegetation type mediates how urbanization reshapes the structure, function, and spatial variation of soil food webs

Urbanization represents one of the major anthropogenic alterations of the
Earth's surface, with significant impacts on biodiversity and its
functions. Soil animals are essential components of biodiversity, playing
integral roles in terrestrial ecosystems. How urbanization reshapes soil
food webs and affects their function and stability is largely unknown. We
assessed the structure and function of soil food webs using stable isotope
analysis and the energy flux approach in urban grasslands and woodlands in
a subtropical city in China, using natural ecosystems with the same
vegetation type as the reference. In urban woodlands, total biomass was 6
times higher, and energy flux was 2 times higher than in the reference
natural forests, resulting in a 50 % lower energy turnover (energy flux to
biomass ratio), and supporting longer food chains. By contrast, urban
grasslands had similar total biomass, total energy flux, and turnover to
wild grasslands, but both the bacterial-to-fungal ratio and soil
consumption-to-feces production ratio increased, suggesting accelerated
soil carbon cycling. Further, we found that urbanization reduced the
stability of trophic connections between food-web nodes (i.e., increased
variation in trophic interaction strengths), especially in woodlands,
probably related to the strong specific predator-prey interactions and
higher environmental heterogeneity of urban green spaces. Overall, against
the generally assumed negative impacts of land-use changes on soil
communities, our study demonstrates that urbanization enhances energy flux
in soil food webs but increases the risk of declining energy flux balance
between different channels and trophic interaction stability. In addition,
the divergent responses to urbanization between different vegetation
emphasize the importance of vegetation-specific management to improve soil
ecosystem functioning (such as C sequestration).