Located at the edge of the Tibetan Plateau, the Qilian Mountains form a significant high-altitude permafrost region. Understanding the stratification characteristics of soil carbon and the response mechanisms under altitudinal variation provides important insights into the carbon pool dynamics across the Tibetan Plateau. Potentilla parvifolia is a shrub species widely distributed at moderate and high altitudes. Recently, with the intensification of global climate change, there have been signs of migration to the high latitudes. This migration affects the microbial community structure and has influence on the soil carbon pools and the carbon cycling processes of ecosystems. In the present study, the rhizosphere soil carbon components and microbial communities of P. parvifolia were evaluated along altitudinal gradients (3204, 3350, 3550, and 3650 m) in the Qilian Mountains. We found that P. parvifolia significantly increased the biomass of soil gram-positive bacteria and fungi at medium and low altitudes (3204, 3350, and 3550 m) (p < 0.05), and significantly increased the contribution of mineral-associated organic carbon (MAOC) to the soil organic carbon (SOC) content when compared to those in bare soil (p < 0.05). Furthermore, P. parvifolia mainly increased SOC content by increasing the contribution of microbial necromass carbon, especially fungal necromass carbon, to MAOC; however, there were no significant differences at high altitudes (3650 m) (p > 0.05). This research enhances our comprehension of the impact of plant migration on SOC and its microbial mechanisms and provides a basis for the development of bioprotection strategies for alpine ecosystem conservation.

Climate change and shrub encroachment affect nematode biodiversity, although shrub species had different effects on below-ground community. Yet, the consequences of shrub species on the nematode beta diversity under future climate change scenarios remain insufficiently explored. Here, we studied the dominant shrub effects on the beta diversity of soil nematode communities along climate gradients on the Qinghai-Tibet Plateau. We investigated soil nematode communities in 31 sites of alpine meadow ecosystems across a 1200 km × 1200 km area with widespread shrub on the Qinghai-Tibet Plateau. We found that shrubs decreased the nematode beta diversity through decreasing the nestedness component at local and landscape scales. Leguminous shrubs had stronger effects on the nematode beta diversity than non-leguminous shrub types at landscape scale. MAP and MAT both significantly increased the negative shrub effects on the nematode beta diversity, but they remained constant for leguminous shrub. The pSEM analysis showed that shrubs had direct and indirect effects on nematode beta diversity via plant species turnover. Our results showed that shrub encroachment, particularly leguminous shrubs, leads to the homogenization of nematode communities. The “warming-wetting” trend will exacerbate shrub effects on the homogenization of nematode communities on the Qinghai-Tibet Plateau. Our study provides insight into the ecological processes that maintain soil biodiversity and biogeographic patterns of soil communities on the Qinghai-Tibet Plateau.