Land-use change alters patterns of soil biodiversity in arid lands of northwestern China

Irrigation-maintained artificial oases (AO) in arid regions of northwestern China provide vital human settlement sites. Recent human population increases has caused rapid AO expansion, mainly through transforming natural grassland to arable and afforested land. Here, we assessed how soil biodiversity is affected by various AO expansion strategies, each representing historical land-use regimes. We sampled six dominant functional groups of soil biota, covering multiple trophic levels: macrofauna consumers (predators and insect herbivores), mesofauna decomposers (Oribatida and Collembola), and microbial decomposers (bacteria and fungi). Sampling was carried out in three AO sites of northwestern China, each containing distinct land uses: natural grasslands (NG; non-irrigated), shrub (Haloxylon ammodendron) plantations (SP; non-irrigated), tree (Populus gansuensis) plantations (TP; irrigated), and arable lands (AL; irrigated). The conversion of NG to SP, TP, and AL eliminated or reduced the abundance of some NG-adapted taxa. Their replacements were exotic species better suited for anthropogenic habitats. As a result, community composition shifted in all six functional groups, with greater differences between NG and TP and AL than between NG and SP. Based on taxonomic gains and losses within each group, we determined that NG to SP conversion positively affected diversity among predators, Collembola, and fungi, but negatively affected diversity of insect herbivores and Oribatida. Bacterial diversity remained unaffected. However, converting NG to TP and AL significantly promoted diversity in all six functional groups, although effect sizes differed. Our results suggest that different AO expansion strategies differentially affected the diversity and structure of belowground communities, which in turn, cascaded down to ecosystem functioning differently. These findings not only contribute to a better understanding of how the diversity and community composition within soil food-webs respond to land-use change but also provide key insights into the development of management strategies for AO ecosystems in drylands to mitigate the negative impact of land-use change on soil biodiversity and ecosystem functioning.