Soil nematode community composition, diversity, and soil properties in an age sequence of Haloxylon ammodendron plantations in an oasis-desert ecotone of northwestern China

Restoration of vegetation and soil ecosystems controls desertification, and soil nematodes have been used as bioindicators of ecosystem restoration, but the efficacy of this method is not clear in desert ecosystem. We selected different ages of Haloxylon ammodendron plantations in a desert-oasis ecotone, in Linze County, northwestern China, and sampled surface soil under and outside the canopy to examine the restoration process of plants and changes in the composition and diversity of nematode communities, and relationship between soil physicochemical properties and nematode genera. The results showed that plantation ages of H. ammodendron had significant effects on total nematodes, omnivores-predators and bacterivores. The numbers of total nematodes increased with plantation ages, and reached 228.0 per 100 g dry soil after 46 years. Bacterivores dominated in soil nematode community, accounting for 50.3-94.1% of nematode numbers. The effect of H. ammodendron on soil nematode communities and physicochemical properties was time-dependent. The significant increase of soil nematodes abundance and diversity appeared from 6 years, and soil physicochemical properties varied significantly after 11 years. Shannon-Weiner diversity index, Evenness index, Trophic diversity (TD) index, and Maturity index showed an increasing trend with plantation age, indicating that the food web became more complex, and soil environment gradually stabilized. Nematode genera in different plantation ages were separated by redundancy analysis (RDA), and soil properties significantly affected the temporal and spatial distribution of nematode communities. We concluded soil nematodes can be used as a biological indicator because they reflect the restoration process of the plant-soil ecosystem.