Continuous cotton cropping affects soil micro-food web

The resource connection between microflora and microfauna in soil micro-food web is of great importance for soil ecosystem in terms of maintaining its quality, productivity, and sustainability. However, the responses of soil micro-food web to continuous cropping (CC) are still unclear at present. In this study, the responses of soil micro-food web to different duration of CC (0 (the control), 5, 10, 15, and 20 years) were investigated in a long-term experiment in Xinjiang, China. The trophic groups of soil nematodes in 0–10 cm and 11–20 cm soil layers were determined according to the trophic habits, oesophageal structure, and predation pattern. The stability and maturity of soil micro-food web were determined by nematode faunal analysis. The connectance was determined according to the predation relationship between nematodes and microbes. The results showed that the abundance of nematodes in the 10- and 20-year CC treatments were higher than that in the control in the 0–10 cm soil layer, and the abundance of nematodes in the 5- and 20-year CC treatments were also higher than that in the control in the 11–20 cm soil layer. In the same soil layer, the abundance of plant parasites in the 10- and 20-year CC treatments and omnivores-predators in the 5- and 20-year CC treatments were higher than those in the control. CC increased the metabolic footprint of omnivore-predators and structure footprint in both soil layers. The soil micro-food web in the CC treatments received fewer disturbances than that in the control, which increased soil nutrients. Meanwhile, the soil micro-food web became stable and mature. The connectance of omnivore-predators channel in the 5-year CC treatment was higher than that in the control in the 0–10 cm soil layer, and the connectance of bacterial channel in the 20-year CC treatment and omnivores-predators channel in the 5-, 10-, and 15-year CC treatments were also higher than those in the control in the 11–20 cm soil layer. Mantel test showed that soil pH, electrical conductivity, organic carbon, total nitrogen, and C/N ratio were key factors affecting soil nematode communities. Therefore, continuous cropping could effectively enhance the soil micro-food web structure and function through bottom-up effects in the cotton fields.