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Oases are common in desert regions of northwestern China and are major sites for human settlement. The implementation of oasis conservation planning has led to afforestation with appropriate shrubs and trees in the native grasslands surrounding inhabited oases. However, little is known about how this Land use change from native grassland to shrub and tree plantations influences the composition of ground-dwelling arthropod communities and the performance of their different trophic groups. To address this, we measured activity density, taxon richness, and relative abundance of four different ground arthropod trophic groups (spiders, beetle predators, beetle herbivores, and beetle detritivores) and several environmental variables affecting arthropod distributions (vegetation cover, ground temperature, soil moisture, soil properties, and leaf litter) along an experimentally established land use change gradient of a mature shrub ( Haloxylon ammodendron) planation, a mature poplar ( Populus gansuensis) plantation and a mature pine ( Pinus sylvestris) plantation, as well as a native grassland from which all cultivated systems were converted. We found that converted shrub plantation had much lower activity density of predatory, herbivorous, and detritivorous beetles; similar activity density of spiders; and similar taxa richness of all four trophic groups relative to the native grassland. However, converted forest plantations regardless of tree species had much higher activity density of spiders, lower activity density of the three beetle groups, much higher richness of predatory beetles, and lower richness of herbivorous and detritivorous beetles. We also found a change in the composition of the ground arthropod community that was largely driven by changes in ground temperature and leaf litter mass. We conclude that conversion of native grassland to shrub and tree plantations can significantly affect ground-dwelling arthropod communities, reducing the activity of ground-dwelling beetle assemblages while increasing that of ground-dwelling spider assemblages. These findings are important for conserving native arthropod diversity in desert ecosystems. [ABSTRACT FROM AUTHOR]

A vast area of native shrub-dominated steppe at the margins of desert oases in arid regions of China had been reclaimed as farmland in the last century for grain production to feed growing human populations. This study evaluated the consequences of this land-use change on the activity density, taxa richness and composition of functional groups (herbivores, predators and detritivores) of ground-dwelling beetles and spiders, which include some important ecological groups of natural enemies of insect pests (e.g. predatory spiders and beetles), pollinators and decomposers (e.g. detritivorous beetles). Ground-dwelling beetles and spiders were collected using pitfall traps in native steppe habitats and adjacent irrigated farmland of different ages (cultivated either for 27 or at least for 90 years). It was found the conversion of native steppe to farmland, regardless of farmland age, led to a significant increase in activity density of predators, with a greater increase in 90-year-old farmland than in 27-year-old farmland, but did not affect their taxa richness. However, native steppe conversion to farmland, regardless of farmland age, led to significant declines in activity density and taxa richness of both detritivores and herbivores, with a much greater decrease of activity or richness in detritivores than in herbivores in both farmland types. We also observed taxa-specific responses to the land conversion within functional groups. The functional composition of the beetle and spider community shifted from a community dominated by detritivores in the native steppe sites to one dominated by predators in the irrigated farmland sites. Our results suggest that the different functional groups of ground-dwelling beetles and spiders responded in a different way to the land conversion. The remarkable increase in predators and the dramatic decline in detritivores by converting natural vegetation to agricultural land are expected to strongly affect the desert ecosystem services such as biological pest control, pollination and decomposition. [ABSTRACT FROM AUTHOR]

Increased demand for food due to the rapidly growing human population has led to extensive conversion of native steppes at the margins of oases in arid lands of northwest China into intensively managed farmlands. However, the consequences of this land-use change for soil microarthropod biodiversity and ecosystem functioning remain unknown. Here we assessed how conversion of a native steppe to irrigated farmlands of different ages affects the abundance and composition of soil microarthropods and how changes in soil microarthropod biodiversity could scale up to influence soil carbon and nitrogen stocks. We sampled microarthropod communities over two growing seasons from native steppes and cultivated soils of a 27-year-old irrigated farmland and a 90-year-old irrigated farmland, both of which were converted from the native steppe. Topsoil properties and bulk and labile pools of carbon and nitrogen, including soil organic carbon, dissolved organic carbon (DOC), microbial biomass carbon (MBC), total nitrogen (TN), inorganic nitrogen (IN), and microbial biomass nitrogen (MBN), were also measured. The conversion of native steppe to either of the two farmlands significantly increased the abundance and taxa richness of three taxonomic groups (mites, collembolans, and others) and four trophic groups (herbivores, predators, detritivores, and fungivores); this effect was greater in the 90-year-old farmland for the abundance of all taxonomic and trophic groups except for herbivores and was similar between the two farmlands for the richness of all taxonomic and trophic groups. Taxonomic and trophic composition of the microarthropod community showed strong shifts in response to conversion of native steppe to either of the two farmlands. Compositional changes were largely mediated by changes in soil environments. Changes in soil carbon and nitrogen stocks due to conversion of native steppe to farmlands followed similar patterns to soil microarthropod biodiversity, but the greater storage of DOC, MBC, TN, IN, and MBN occurred in the 90-year-old farmland. Our results suggest that soil microarthropod communities are affected positively by native steppe conversion to farmland and farmland age, and that increased microarthropod biodiversity significantly improved the ability of soils to retain carbon and nitrogen. [ABSTRACT FROM AUTHOR]