Effects of soil fauna on soil carbon accumulation under organic amendments: Insights from community composition and energy flux

Abstract

Soil fauna plays an indispensable role in soil organic carbon (SOC) cycling. Organic amendments are anticipated to enrich the soil with organic carbon and enhance the soil faunal abundance. However, the specific mechanisms by which soil fauna regulates carbon accumulation under these organic amendments are not fully elucidated. We carried out a six-year field experiment including no fertilizer application, conventional chemical fertilizer, and partial substitutions of urea with maize straw and cattle manure. We aimed to explore the connections between soil faunal community and carbon fractions under organic amendments. Our findings indicated that organic amendments elevated SOC and mineral-associated organic carbon (MAOC) by 16.7 %–25.9 % and 7.5 %–10.1 %, respectively, relative to the unfertilized control. Fertilization regimes modified the composition of arthropod and nematode communities. Notably, Prostigmata and Oribatida positively correlated with microbial necromass carbon, while nematode community composition was positively associated with neutral sugar accumulation. Under manure amendment, the concentration of neutral sugar positively correlated with the ratio of MAOC to particulate organic carbon (POC). Moreover, compared with conventional chemical fertilizer, straw amendment increased total nematode biomass by 71.4 % and energy flux by 67.3 %, enhancing plant-derived carbon formation through root energy pathways. In contrast, manure amendment increased fungivorous nematodes' relative carbon flux to 18.6 %, showing preferential fungal-mediated carbon channeling. These differential effects underscore the significance of integrating faunal-mediated processes into strategies for managing soil carbon dynamics and developing sustainable agroecosystem fertilization practices.