Abstract: Shaniodendron subaequale, a tertiary relict species endemic to China, is designated as a nationally protected wild plant species due to its significant evolutionary status bridging gymnosperms and angiosperms. The plant-associated microbiome is considered the second genome of plants. Phyllosphere bacteria significantly influence plant growth and environmental adaptability. The characteristics and geographical distribution patterns of the bacterial community in S. subaequale phyllosphere are unknown. This study aimed to investigate the composition and diversity of S. subaequale phyllosphere bacteria in its primary distribution areas, as well as the influences of geographical features, soil physical and chemical properties, and leaf physiological and biochemical indices on phyllosphere bacterial composition and diversity. Leaves of S. subaequale from six native sites were collected. The phyllosphere bacterial community was determined by high-throughput sequencing technology. Moreover, leaf physiological and biochemical indices and soil physical and chemical properties in each site were measured. The results revealed a high relative abundance of Sphingomonas, Massilia, and Amnibacterium in the phyllosphere of S. subaequale in all the six sites. Leaf bacterial composition was significantly distinct in different sites. In particular, the phyllosphere bacterial composition in plants from Huzhou City, Zhejiang Province was significantly different from that of other sites. The phyllosphere bacterial diversity was greatly affected by the latitude differences among the sites. However, the effects of leaf physiological and biochemical characteristics and soil physical and chemical properties on the bacterial composition and diversity in the phyllosphere of S. subaequale were more pronounced. This study reported the presence of a wide range of bacterial taxa in S. subaequale phyllosphere. Moreover, there were significant differences in the phyllosphere bacterial composition and diversity in S. subaequale across different sites, which were mainly regulated by leaf defense-related metabolites and soil nutrients. The results provide a theoretical basis for preserving the environment of microecology in S. subaequale and thus strengthening species conservation.

Key words: Shaniodendron subaequale, phyllosphere bacteriome, bacterial diversity, biogeographic distribution pattern, soil physical and chemical properties