Abstract
Soil microorganisms and physicochemical properties are considered the two most influencing factors for maintaining plant diversity. However, the operational mechanisms and which factor is the most influential manipulator remain poorly understood. In this study, we examine the collaborative influences of soil physicochemical properties (i.e., soil water, soil organic matter (SOM), salinity, total phosphorus and nitrogen, pH, soil bulk density and fine root biomass) and soil microorganisms (fungi and bacteria) on plant diversity across two types of tree patches dominated by big and small trees (big trees: height ≥ 7 m and DBH ≥ 60 cm; small trees: height ≤ 4.5 m and DBH ≤ 20 cm) in an arid desert region. Tree patch is consists of a single tree or group of trees and their accompanying shrubs and herbs. It was hypothesized that soil physicochemical properties and microorganisms affect plant diversity but their influence differ. The results show that plant and soil microbial diversity increased with increasing distances from big trees. SOM, salinity, fine root biomass, soil water, total phosphorus and total nitrogen contents decreased with increasing distance from big trees, while pH and soil bulk density did not change. Plant and soil microbial diversity were higher in areas close to big trees compared with small trees, whereas soil physicochemical properties were opposite. The average contribution of soil physicochemical properties (12.2%–13.5%) to plant diversity was higher than microbial diversity (4.8%– 6.7%). Salinity had the largest negative affect on plant diversity (24.7%–27.4%). This study suggests that soil fungi constrain plant diversity while bacteria improve it in tree patches. Soil physicochemical properties are the most important factor modulating plant diversity in arid desert tree patches.