Effects of Irrigation Methods on Leaf Nutrients and Phyllosphere Microbial Community Structure of Zanthoxylum planispinum var. dingtanensis

Scientific irrigation can not only achieve efficient water resource utilization but also help improve crop yield and quality. To clarify the effects of different irrigation methods on leaf nutrient status and phyllosphere microbial community structure in Zanthoxylum planispinum var. dingtanensis, this study established three treatments—no irrigation (control), sprinkler irrigation, and flood irrigation—in the Huajiang Rocky Desertification Control Experimental Area in Guizhou, and systematically measured leaf total carbon (TC), total nitrogen (TN), total phosphorus (TP), and total potassium (TK) contents. Meanwhile, high-throughput sequencing of bacterial 16S rDNA and fungal ITS was used to analyze phyllosphere microbial community composition and to explore its response to leaf nutrient factors. The results showed that leaf nutrient contents did not differ significantly among irrigation treatments (p > 0.05). Flood irrigation had the lowest TK content and relatively large within-treatment variation, whereas sprinkler irrigation showed relatively low within-treatment variation for all nutrient indices. Bacterial Chao1, Shannon, and Simpson indices did not differ significantly among treatments; the fungal Chao1 index under sprinkler irrigation was significantly lower than under no irrigation and flood irrigation (p < 0.05). The dominant bacterial phyla were Cyanobacteria, Proteobacteria, Actinobacteria, and Bacteroidetes. The relative abundance of Bacteroidetes under sprinkler irrigation was significantly higher than under flood irrigation (p < 0.05); Firmicutes under flood irrigation was significantly higher than under no irrigation and sprinkler irrigation; in addition, Hymenobacter was significantly enriched under sprinkler irrigation. The dominant fungal phyla were Ascomycota and Basidiomycota. Under sprinkler irrigation, the relative abundance of Ascomycota was significantly lower than under no irrigation, whereas the relative abundances of Basidiomycota under sprinkler and flood irrigation were significantly higher than under no irrigation (p < 0.05). In addition, the relative abundance of Alternaria under flood irrigation was significantly higher than that under sprinkler irrigation. Redundancy analysis (RDA) indicated that leaf nutrient indices (TC, TN, and TP) were not significantly correlated with the overall phyllosphere microbial community structure (p > 0.05), whereas TK was one of the potentially important environmental factors influencing the distribution of dominant phyllosphere microbial genera. In summary, different irrigation methods did not significantly alter the leaf nutrient content of Zanthoxylum planispinum var. dingtanensis but significantly reshaped the phyllosphere microbial community structure and specifically increased the relative abundances of Bacteroidetes, Firmicutes, Hymenobacter, and other taxa. This study provides preliminary empirical evidence and data support for understanding the regulatory mechanisms by which irrigation measures affect phyllosphere microecology in the cultivation of Zanthoxylum planispinum var. dingtanensis in rocky desertification areas.