Effects of Caragana intermedia on soil nematode communities in a steppe desert region

This study examined the effect of shrubs on soil nematode communities. We took the dominant shrub species Caragana intermedia in the Inner Mongolia steppe desert area as the target plant and investigated the soil nematode communities composition and structure under C. intermedia shrub canopies and in open areas at different soil depths (0 − 10, 10 − 20, 30 − 40 cm) using the wet funnel method (Baermann method). The results showed that 1) The total number of soil nematodes in the top soil layer was higher under C. intermedia shrub canopies than in the open areas, but the species richness and Shannon-Wiener index were not significantly different between the canopy conditions (P > 0.05). The total number and Shannon-Wiener index of the soil nematodes decreased as the soil depth increased. 2) The number of bacterial-feeder and fungal-feeder nematodes in the top soil layer was higher under the shrub canopies than in open areas. Soil depth significantly affected the total number of bacterial-feeder, plant-parasitic, and omnivorous-predation nematodes, and their total numbers were highest at the soil surface and in the subsurface soil layer. 3) Shrubs had a significant effect on PPI/MI values (P < 0.05), which showed that the values were higher in open areas than under the shrub canopies. Soil depth had no significant effect on the PPI/MI values (P > 0.05). 4) As the soil depth increased, the community structure of the soil nematodes changed to the resident trophic groups (persister, cp3 – cp5) under the shrub canopies, and to the colonizer trophic groups (colonizer, cp1 or cp2) in open areas. The RDA analysis revealed that available P and available K are the primary environmental factors influencing soil nematode communities, and that nematodes communities belonging to different taxa and trophic groups respond to environmental conditions in different ways.