Community characteristics of soil nematode in Shushanggan apricot plantations of different ages in the Yili River Valley

Abstract:【Objective】Nematodes are one of the classic indicators of soil health. This study aimed to clarify the composition of soil nematode community and its responsive characteristics to soil physicochemical properties in Shushanggan apricot plantations in Yili River Valley, so as to provide a theoretical basis for sustainable management of Shushanggan apricot plantations.【Methods】In this experiment, soil samples of Shushanggan apricot plantations aged at 4, 8, 10 and 14 years and nearly barren land were collected in Sangong township, Huocheng county in September, 2023. The geographical location and elevation of the sampling site were determined by GPS. Five undertree forestlands of Shushanggan apricot plantations with different planting years were selected as the quadrates (20 m´20 m), and the soil layers were selected at 0-10 cm and 10-20 cm. Five small samples (10 cm´10 cm) were selected from the plantation land under each tree, 0.5 m away from the base of trunk and mixed into one soilsample by five-point sampling method. A total of 50 soil samples were collected from the five plots. An appropriate amount of soil sample was taken from each layer of each quadrate, mixed evenly and airdried to determine the soil physicochemical properties. Soil nematodes were isolated by sucrose density gradient centrifugation and identified by morphological method. To investigate the number, composition and ecological function index of soil nematode community in Shushanggan apricot plantations, this research was conducted to analyze the relationship between soil nematode groups and soil physicochemical properties.【Results】A total of 7066 nematodes were isolated from all plots, and 52 genera of nematodes were identified, belonging to 2 classes, 6 orders and 23 families, with an average density of 373 nematodes per 100 g of dry soil. The density of soil nematodes in Shushanggan apricot plantations decreased first, reaching the highest in 10 years (752 nematodes per 100 g dry soil), and then increased. The dominant genera in the Shushanggan apricot plantations of different ages were Acrobeloides, Paratylenchus and Microdorylaimus. Among them, the dominant genera of the 4- and 10- year- old apricot plantations are Acrobeloides, Chiloplacus, Aphelenchus and Microdorylaimus. The dominant genera of the 8- and 14-year-old plantations are Pararotylenchus, Rotylenchus and Helicotylenchus. According to the c-p value, c-p2 and c-p3 were the main groups. The density of soil nematode in the 8-, 10- and 14- year-old plantations was higher in the 10-20 cm soil layer, and higher in the 0-10 cm soil layer on the 4 years old plantations. There were significant differences in diversity index (H′) between 10 years old Shushanggan apricot plantations and barren land (p＜0.05). Soil nematodes diversity index (H′ ) in Shushanggan apricot plantations decreased first, reaching the lowest in 10- years, and then increased. The plant parasitic index (PPI) in barren land was significantly lower than that in Shushanggan apricot plantations of different ages. The maturity index (MI) of the 4-year-old Shushanggan apricot plantations was significantly lower than that of other plots, while the Wasselska index (WI) was significantly higher than that of other plots. The nematode channel ratio (NCR) of the 8-year-old plantations was significantly lower than that of the 10-year-old Shushanggan apricot plantations, while the MI and PPI of the 8- year-old plantations were the highest. The total kalium (TK), pH and calcium (Ca) content in the soil were the main environment factors affecting the composition of soil community in Shushanggan apricot plantations (p＜0.05). Correlation analysis showed that TK was negatively correlated with c-p1 and bacterivores nematodes (Ba). Soil moisture content (SM) was positively correlated with all nematode trophic groups and c-p groups. pH and Ca content were significantly and positively correlated with Fu and negatively correlated with c-p3 and Pp.【Conclusion】After the conversion of barren land to Shushanggan apricot plantations, the tolerance nematodes c-p2 and c-p3 increased and the sensitivity nematodes c- p4 decreased, indicating that Shushanggan apricot plantations were disturbed to varying degrees in different age’s plantations, and Shushanggan apricot plantations were disturbed the most at 4 years old, followed by 10 years old. Although the density of nematode in the 10- year- old Shushanggan apricot plantations was higher than that in other plots, the stability and diversity of nematode community were poor due to human interference, while the diversity and stability in the barren land were higher than those in other plots, indicating that the soil nematode diversity was higher in undisturbed ecosystems. In general, the disturbance of 4- and 10-year-old plantatios was larger, and the disturbance of 8- and 10- year-old ones was smaller. However, the soil enrichment degree in 4- and 10-year-old Shushanggan apricot plantations was higher, and the food web structure was more mature. Instead, the soil food chain of 8- and 14-year-old plantations was shorter, and the soil organic matter conversion ability was poor. In conclusion, the main trophic groups of 4- and 10- year-old plantations were Bacterivores, and the soil health was good. The main trophic groups of 8- and 14-year-old plantations were Fungivores, and thesoil health was poor. The results provided theoretical basis for rational planting of Shushanggan apricot plantations.