[Micro-morphological Characteristics of Particles on Holly and Ligustrum Leaf Surfaces and Seasonal Changes in...

The characteristics of particles and microorganisms on leaf surfaces have great significance for the near-surface environment and ecology. Here, fresh leaves of holly and Ligustrum were examined from different functional areas in Qingdao. Environmental scanning electron microscopy was used to observe particles and microorganisms on the leaf surfaces during different seasonal, and Illumina high-throughput sequencing was performed to analyze the phyllosphere bacterial community structure. The results showed that the retention of TSP on leaves in autumn and winter was higher than in spring and summer. The leaves of the two plants were more likely to retain PM₁₀ and PM_2.5; however, the dust retention capacity of holly leaves was higher than that of Ligustrum, especially for particle sizes greater than 10 μm. The numbers of particles on the leaf surfaces along an urban main road were higher than in two other locations, and were greatly affected by ground dust and automobile exhaust emissions. The community structure of phyllospheric microorganisms showed distinct seasonal variation, with different types of fungi, fungal spores, and mycelium observed on the leaf surfaces. Mycelium was more frequently detected on leathery leaves, and fungal spores with even folds were detected on the leaf epidermis of Ligustrum. The relative abundances of phyllospheric microorganisms were highest on leaves from an urban park, explained by a positive effect of humidity on growth. Significant differences in bacterial community abundance were observed between seasons. Specifically, bacterial abundance was highest in spring and lowest in summer. γ-Proteobacteria were the dominant bacteria, and the two plants shared a similar core microbial community. In addition, the phyllospheric bacterial community structure of leaves from urban arterial roads with ground dust pollution was significantly different from the leaves collected from other city areas. Our research results suggest a significant correlation between the leaf-surface particles and microbial community structure on representative plants in different areas of the city, which provides reference information for urban greening activities.