Community structure and diversity of soil nematodes in different slope directions of wild cherry plum forests in Xinjiang, China

【Objective】This study elucidates the spatial differentiation pattern of nematode communities in soils in slopes facing different directions and provides reference for the conservation and scientific management of wild cherry plum forest population.【Methods】Through field investigations, soil nematodes were collected from four sites (20 m × 20 m) in the Fushou Mountain Scenic Area of Daxigou, Huocheng county in May 2024, including sunny slopes, semi sunny slopes, semi shaded slopes, and shaded slopes (The geographical location is 44°25′29″ to 44°25′39″ N, 80°45′20″ to 80°46′3″ E, the altitude is 1 260.80-1 376.50 m, and the slope is 16.5° to 37.0°). Five plots were set up with duplicate samples at 0-10 cm and 10-20 cm depths in each plot. A total of 20 plots were set and soil samples col-lected using the five-point sampling method. Soil samples from different sampling points in the same plot were pooled to form a single soil sample. Tree roots, stones, and other debris were removed from the soil samples, which were then put in self sealing bags, labelled and stored in a laboratory freezer at 4 ℃. One soil sample was used for separating and extracting nematodes; another was used to determine the physical and chemical properties of soil. The structural characteristics of soil nematode communities and soil physicochemical properties on different slopes of cherry plum forest in Huocheng County, Xinjiang were analyzed.【Results】The results showed that a total of 4101 soil nematodes were captured, belonging to 60 genera, and the dominant genera of the nematodes were the spine-bladed genus Coslenchus and the forked-needle genus Boleodorus, which accounted for 23.80% of the total number of nematodes captured. The dominant nematode genera were Coslenchus and Boleodorus, accounting for 23.80% of the total number of collections. Among them, there were 550 nematodes belonging to 30 genera in Yangpo soil, with an average density of 353.02 nematodes per 100 g of dry soil. The dominant genera were Boleodorus and Merlin. There were 906 nematodes belonging to 35 genera in the soil of the semi sunny slope, with an average density of 472.24 nematodes per 100 g of dry soil. The dominant genera were Lelenchus, Basiria, and Merlin. There were 1482 nematodes belonging to 49 genera in the semi shaded soil, with an average density of 947.48 nematodes per 100 g of dry soil. The advantageous genera were Coslenchus and Boleodorus, which belong to the spine cushioned blade genus and the forked needle genus. There were 1163 nematodes belonging to 40 genera in the shady slope soil, with an average density of 729.74 nematodes per 100 g of dry soil. The advantageous genera were Coslenchus, Boleodorus, and Acrobeles. In the first soil layer (0-10 cm) and the second layer (10-20 cm), the nematode density was highest in the soil of the semi shaded slope and lowest in that of the sunny slope. And as the depth of the soil layer increased, the density of soil nematodes gradually decreased. In terms of functional groups, the relative abundance of phytophagous nematodes and the relative abundance of c-p2, was the highest in the soils at the four slope orientations. The density and number of soil nematodes were highest on semi shaded slopes and lowest on sunny slopes, with obvious surface aggregation characteristics. In terms of diversity and ecological index, the diversity index (H'), species richness index (SR), enrichment index (EI) and the maturity index (MI) were different in vertical distribution. SR, MI and EI of the semi-negative slope were the highest. The nematode channel ratio (NCR) was greater than 0.5 and the Wasselska index (WI) was less than 1, indicating that parasitic nematodes of wild cherry plum forest plants occupied a dominant position in the community, and the ecosystem had low antiinterference ability. Organic matter decomposition is a bacterial based decomposition pathway. From the nematode symbiotic network, there were differences in the collinear network of soil nematodes in different slope orientations. Among them, the number of nodes, edges, edge density, and connectivity of the nematode network in the semi shaded slope soil were the highest, indicating that in this habitat, the nematode collinear network was more complex and had a more stable food web structure inside. The linear regression model showed that the complexity of nematode networks was significantly positively correlated with external soil physicochemical factors (nitrate nitrogen and available phosphorus) (P＜ 0.05), and there was also a significant positive correlation between soil nematode richness index and network complexity (P＜0.01). Non metric multidimensional scale (NMDS) analysis was conducted on soil nematodes in different slope orientations and vertical distributions (different soil layers), and the results showed significant differences in the community structure of soil nematodes in different slope orientations (P＜0.05). There was no significant difference in soil nematode community structure between different soil layers (first and second layers) (P＞0.05), indicating that slope orientation is a key factoraffecting soil nematode community structure (ANOSIM, r＞0, P＜0.05). Correlation analysis showed that soil available phosphorus was the main factor affecting the composition and diversity of nematode community. In addition, soil organic matter, total phosphorus, nitrate nitrogen, ammonia nitrogen and electrical conductivity also affected the composition of nematode community.【Conclusion】The community structure of soil nematodes significantly differs among different slope directions, the semi shaded slope has the best ecological environment quality, and the changes in soil environmental factors in different slope directions are the main factors driving the changes in soil nematode communities.