Effects of maize and forage planting on the community structure of ground-dwelling arthropods in oasis farmland

Intensive management of oasis farmland has pronounced negative effects on the diversity and function of soil-dwelling animals. Ground-dwelling arthropods comprise an important group of soil macrofauna that inhabit oasis agroecosystems. Their community composition and functional traits are particularly sensitive to changes in farmland plant coverage. In this study, we systematically investigated the changes in the species composition and quantity of ground-dwelling arthropods during the growing and non-growing seasons of maize field and froages (vetch and alfalfa) fields in the Zhangye Oasis of the Hexi Corridor, China, using a trap method. We also determined the influence of farmland crops and changes in grazing cover on arthropod community structure. We detected significant differences in the community composition of ground-dwelling arthropods in the maize, vetch, and alfalfa fields, as well as seasonal variation. The community composition in alfalfa field was significantly different from that in both maize and vetch fields during the growing season, although comparatively little difference among fields was detected in the non-growing season. During the growing season, the activity density and species richness, diversity, and evenness indices of ground-dwelling arthropods in the alfalfa field were significantly higher than those of arthropods inhabiting the maize and vetch fields. During the non-growing season, the species richness and diversity indices of ground-dwelling arthropods in the alfalfa and vetch fields were significantly higher than those in the maize fields. Furthermore, during the growing season, the activity density of predatory ground-dwelling arthropods in the alfalfa field was significantly higher than that in the vetch and maize fields. Similarly, during both the growing and non-growing seasons, the activity density of phytophagous arthropods in the alfalfa field was significantly higher than in the vetch and maize fields. However, in both seasons, the activity density ratio of predatory phytophagous arthropods in the maize and vetch fields was significantly higher than that in alfalfa field. In addition, we found that in the alfalfa field, the activity densities of herbivorous ground-dwelling arthropods (including those in the families Acridoidea, Thripidae, Cicadellidae, and Aphididae) were significantly higher than those in the vetch and maize fields. Similarly, in the alfalfa field, the activity densities of predatory ground-dwelling arthropods (including those in the families Gnaphosidae, Lycosidae, and Carabidae) were significantly higher than those in the other two fields. Collectively, the findings of this study reveal that the planting of perennial herbage in arid areas can contribute to increased number and diversity of beneficial populations among surface-dwelling arthropods inhabiting oasis farmlands, notably by promoting increases in the diversity and population size of herbivorous arthropod species. This in turn contributes the enhanced biological control of farmland pests.