Abstract: To clarify the improvement effect of Caragana korshinskii plantation on fragile eco-environment in semi-arid areas, we selected four C. korshinskii plantations with different ages (4-, 14-, 24-, and 34-yea-old) in the mountainous area of southern Ningxia as the research objects, where was one of the key C. korshinskii planting areas on the Loess Plateau. We investigated the composition, structure, and diversity of soil nematode communities, and analyzed their relationships with soil properties, to explore the evolution of soil nematode community and their environmental influencing factors in the restoration process of C. korshinskii plantation in the semi-arid region of the Loess- Plateau. The results showed that the stand age of C. korshinskii plantation significantly affected soil nematode abundance, which increased first and then decreased with increasing stand age, and peaked in the 14-year-old plantation. The nematode community composition and trophic group structure differed greatly among different stand ages. The percentages of omnivorous-predatory and plant-parasitic nematodes were highest in the 14- and 24-year-old plantations (40.3% and 61.3%), respectively, while that of bacterial and fungal-feeding nematodes reached the maximum in the 4- and 34-year-old plantations, respectively. The ecological indices of soil nematode communities changed with stand age. The maturity index, Wasilewska index, and structure index all reached the maximum in the 14-year-old plantation, while those three ecological indices as well as the Shannon diversity index and Pielou evenness index of nematode community decreased to the lowest in the 24-year-old C. korshinskii plantation, indicatingdecreased soil biodiversity and poor ecosystem restoration. Across the chronosequence of C. korshinskii plantations, soil water content, organic carbon concentration, total nitrogen concentration, and microbial biomass carbon were the main influencing factors driving the changes in the abundance and community composition of soil nematodes. Such changes in soil nematode communities can effectively indicate soil health and ecosystem restoration status, which are of great significance for the comprehensive evaluation of eco-environmental impacts of C. korshinskii plantations.

Key words: semi-arid region of Loess Plateau, vegetation restoration, Caragana korshinskii plantation, stand age, nematode community.