Abstract: Aims Plants and soil microorganisms play crucial roles in regulating the function and stability of terrestrial ecosystems. Exploring the pattern variations of the community composition and diversity of plant and soil microorganisms and their driving mechanisms along elevation gradients is better understanding their response to terrestrial ecosystems and the maintenance mechanisms of biodiversity under global change. Methods In this paper, we designed a vertical gradient experiment with three different grassland types in the northern slope of Kunlun Mountain. Through community investigation in field with climate data, and high-throughput sequencing was used to assess soil microbial for baterial 16S RNA and fungal internal transcribed spacer(ITS) regions on Illumina NovaSeq. The variation patterns of community structure, composition and species diversity of plant and soil microorganisms along altitude gradient (2 200–3 800 m) and their potential relationships were studied. Important findings (1) The species diversity and productivity of aboveground plant community, soil microorganism’s diversity (including bacteria and fungi) and soil nutrients increased monotonously along the altitude gradient, and the peak value was found in the alpine steppe. Soil fungi were more sensitive to environmental gradient than bacteria. Aboveground plant community and soil fungal community had a significant variation along altitude gradient, but the structure and composition of soil bacterial community did not change significantly. Species diversity and aboveground biomass of plant community were significantly related to the diversity of soil microbial community, but the relationship with bacterial diversity was stronger than that of fungi. The species diversity of soil microorganisms and plant community was positively correlated with mean annual precipitation (MAP) and soil nutrients (carbon, phosphorus and potassium) content, but negatively correlated with mean annual air temperature (MAT). The pattern analysis showed that altitude (geographical distance) and climate factors had greater contribution on soil microorganisms and plant biodiversity than soil factors. The variation of climate factors (MAT and MAP) caused by altitude gradient were the dominant driving factors for community dynamics of plant and soil microorganisms, but their roles were different. Soil nutrients also play an important role in biodiversity of soil microorganisms and plant community. In summary, the regional distribution pattern of aboveground plant and soil microbial communities in mountain steppe is co-regulated by climate and soil factors caused by altitude gradient in the arid region. This study revealed that climatic factors in arid areas were the dominant factors that drive the variations of distribution pattern and structural composition of plant and soil microbial communities in mountain steppe ecosystems, and soil microbial diversity (especially bacteria) played a vital role in improving the productivity of grassland communities. This research provides scientific guidance for grassland ecosystem management and biodiversity protection in arid areas.

Key words: Arid region, Mountain steppe, Community composition, Biodiversity, Altitude gradient, Driving mechanism