Long-term vegetation restoration promotes the stability of the soil micro-food web in the Loess Plateau in North-west China

Soil nematode communities play a significant role in soil ecosystems. Indeed, soil nematode metabolic carbon footprint, based on nematode biomass, is used to evaluate ecosystem functioning and assess nematode response to ecosystem nutrient enrichment. However, it is unclear whether vegetation restoration affects the metabolic carbon footprint of soil nematodes and soil food webs. We selected five periods for this study including: (1) farmland (0 years), (2) grassland (30 years), (3) shrubland (60 years), (4) pioneer forest (100 years), and (5) climax forest (160 years). Community composition, diversity, and metabolic footprint of soil nematodes, and carbon flow changes through the food web were investigated. The Shannon diversity (H') index of the soil nematode community increased in the process of restoration, and the Pielou index (J') appeared to be lower at 30 years after vegetation restoration than at 60, 100, and 160 years. The connectance of the soil nematode food web values increased continuously, from 30 years to 160 years, reaching the highest value at 100 and 160 years, which indicated that the food web had the strongest carbon flow at 100 years after vegetation restoration on the Loess Plateau, indirectly reflecting the stability of the soil food web. Bacteria were more important than fungi in the carbon flow in the food web during vegetation restoration. The study demonstrated that vegetation restoration promoted the input of the availability of external resources, enhanced the metabolic activity of omnivorous carnivores and the soil carbon flow, and stabilized the soil food web. However, the increase in vegetation restoration time not only changed the species composition but also changed the carbon input, due to the lack of interference by agriculture. Therefore, the intrinsic mechanism needs to be studied further.