Seasonal patterns of the abundance of ground-dwelling arthropod guilds and their responses to livestock grazing in a semi-arid steppe

The ground-dwelling arthropods is a key component in grassland ecosystem. Many studies have been done on the effects of grazing intensity and grazer species on arthropods in grassland ecosystems, but the information on the effects of grazing timing and frequency are less available. We investigated the abundance of ground-dwelling arthropods in spring, summer and autumn in an experimental steppe grassland that had experienced four grazing management (no-grazed control (T0), June-and-August grazing (T1), July-and-September grazing (T2) and plant growing season grazing (T3)) over four years in central Inner Mongolia. We found that (i) Phytophagous, parasitic and detritivore arthropods were more abundant in autumn than spring, whereas predatory and omnivorous arthropods were less abundant in autumn than spring and summer. (ii) Grazing reduced the abundance of detritivore or predatory arthropods, but not that of omnivorous arthropods. (iii) Grazing had no effects on the relative abundance of different arthropod guilds in spring, but T2 and T3 reduced the relative abundance of detritivore or predatory arthropods, but increased that of omnivorous arthropods in summer. (iv) The variations in the abundance of arthropod guilds was closely associated with the changes in vegetation attributes induced by current-year grazing (height, standing biomass and quality), not by grazing over multiple years (relative biomass of dominant plant species, soil available N and total C:N ratio). Our results provide new insights into the mechanisms of the biological interactions across tropic levels under different management and is helpful to the development of management regimes for steppe ecosystem conservation.