Effects of continuous cropping on the structure and function of soil nematode communities in potato

Potato is a vital crop for global food security. However, long-term continuous cropping leads to soil degradation and intensifies soil-borne diseases, posing a significant threat to sustainable production. Soil nematodes are important bioindicators of soil health and food web dynamics. In this study, we investigated nematode community succession and its underlying drivers in a 15-year potato monoculture experiment in Dingxi, Gansu, China. Four continuous cropping durations—1, 5, 10, and 15 years (T1, T5, T10, T15)—were evaluated using high-throughput sequencing and soil physicochemical analysis. Results showed that prolonged continuous cropping significantly reduced soil pH from 8.28 (T1) to 8.14 (T15) (P < 0.05) and decreased soil organic matter content, particularly between T5 and T15. In contrast, available nitrogen, phosphorus, and potassium increased and peaked at T15 (P < 0.05), resulting in a disrupted C:N:P stoichiometric balance. Beta-diversity analysis (PCoA) indicated that years 5-10 represent a critical transition period in nematode community structure, explaining 57.06% of the variation. The relative abundance of bacterivorous nematodes increased from 15% (T1) to 24% (T15), with Monhysterida rising from 9% to 15% (P < 0.05), suggesting a shift in the soil food web from a fungal- to a bacterial-dominated energy pathway. Plant-parasitic nematodes followed a nonlinear “rise-then-fall” pattern, peaking at T5 and declining significantly at T10 and T15 (P < 0.05). After fifteen years of continuous cropping, potato economic yield declined by 39.55%, the rot rate by weight increased 15.8-fold, and the proportion of marketable potatoes declined sharply. Redundancy analysis (RDA) and Mantel tests identified soil organic matter and pH as key drivers of nematode community succession. Based on these findings, we propose a two-stage succession model for nematode communities under continuous cropping. We further suggest that applying high-carbon organic amendments to restore fungal-dominated energy channels is a promising strategy to alleviate continuous cropping obstacles and support the ecological restoration of degraded farmland.