Soil nematode community responses along a Sophora alopecuroides encroachment gradient in degraded grasslands of the Ili River Valley

Abstract

Abstract

The encroachment of Sophora alopecuroides is becoming increasingly common in degraded grasslands of the Ili River Valley, but its associations with belowground nematode communities remain unclear. In this study, four plot types representing different encroachment intensities were selected in the Tohulasu Grassland: non-encroached B, lightly encroached L, moderately encroached M, and heavily encroached H plots. Soil nematode abundance, genera richness, trophic guilds, life-history strategy groups, ecological indices, and soil physicochemical properties were analyzed. A total of 25,754 nematodes belonging to 64 genera were identified. Nematode abundance increased with encroachment intensity and was highest in H plots, reaching 2.27 times that in B plots. Plant-parasitic nematodes were significantly more abundant in H and M plots than in B plots, while bacterial feeders and omnivorous-predatory nematodes increased significantly under heavy encroachment. Among life-history strategy groups, colonizer–persister group 2 increased mainly under moderate to heavy encroachment, and cp 4 was significantly more abundant in H plots than in the other three plot types. In contrast, genera richness and community-level ecological indices showed no significant differences among encroachment intensities. Mantel tests detected no significant correlations between trophic guilds and individual soil variables, but weak correlations were observed between selected guilds and soil variables, including BA with nitrate nitrogen, soil organic matter, and pH, OP with electrical conductivity, and fungal feeder nematodes with soil water content. In contrast, cp3 was significantly correlated with nutrient-related variables, including soil organic matter, total nitrogen, total potassium, nitrate nitrogen, available phosphorus, and available potassium, while cp2 was significantly correlated with total potassium and available phosphorus. Redundancy analysis retained soil organic matter, soil water content, total phosphorus, and electrical conductivity after collinearity reduction, but the overall model was not statistically significant; therefore, the ordination results were interpreted as exploratory patterns.