Abstract:

Aims: Phyllosphere microorganisms are crucial for host plant health; however, the diversity patterns and underlying mechanisms of both phyllosphere endophytic and epiphytic bacterial communities in desert shrubs of arid regions remain poorly understood. This study aimed to systematically investigate the diversity characteristics, influencing factor, and assembly mechanisms of phyllosphere endophytic and epiphytic bacterial communities in six typical desert shrubs. 

Methods: The study focused on six typical desert shrub species in Turpan, Xinjiang. Using high-throughput sequencing of the 16S rRNA gene combined with statistical approaches including principal coordinates analysis, variation partitioning, structural equation modeling, and null models, we analyzed the diversity characteristics, influencing factors, and assembly mechanisms of phyllosphere endophytic and epiphytic bacterial communities. 

Results: The diversity of epiphytic bacterial communities differed significantly among the six desert shrub species (P < 0.05), while no significant interspecific differences were observed in endophytic bacterial community diversity (P > 0.05). Significant differences in bacterial community diversity were detected between the leaf surface (epiphytic) and interior (endophytic), with the Shannon index and Pielou’s evenness index being significantly higher in endophytic than in epiphytic communities (P < 0.05). Variation partitioning analysis revealed that leaf physiology independently explained a greater proportion of variation in endophytic bacterial communities (35.10%) than leaf morphology (13.42%) or leaf nutrients (0.62%). In contrast, leaf morphology independently explained more variation in epiphytic bacterial communities (32.75%) compared to leaf physiology (6.75%) and leaf nutrients (0.52%). Structural equation modeling indicated that leaf physiological and chemical traits not only directly affected bacterial community structure on both leaf surfaces and interiors, but also indirectly influenced it through leaf morphological traits. Additionally, leaf morphology indirectly shaped community structure via its effect on bacterial α diversity. Null model analysis demonstrated that stochastic processes dominated the assembly of both epiphytic (66.67%–93.33%) and endophytic (80.00%–100.00%) bacterial communities, with ecological drift being the core influencing factors. 

Conclusion: This study reveals that in extremely arid desert shrubs, epiphytic bacterial community diversity is primarily shaped by plant species identity and leaf morphology, with significant interspecific differences, whereas endophytic community diversity is mainly driven by leaf physiology and shows no significant interspecific variation. Moreover, stochastic processes, particularly ecological drift, play a dominant role in the assembly of both community types. These findings provide new theoretical insights into the mechanisms sustaining biodiversity in vulnerable desert ecosystems under global climate change.

Key words: desert shrubs, endophytic and epiphytic bacterial community diversity, community assembly, leaf functional traits, host plant identity, hyper-arid regions