Changes in Phyllosphere Microbial Communities of Pinus tabuliformis after Infestation by Bursaphelenchus xylophilus

Phyllosphere microbial communities have an important role in plant growth and resistance to pathogen infection and are partially influenced by leaf characteristics. Pinewood nematode, Bursaphelenchus xylophilus, is one of the greatest threats to pine trees and is spreading all over the world. However, studies on the resistance of plant-microbe interactions to pathogens during the nematode's pathogenesis and the relationships of leaf chemical characteristics caused by pinewood nematode and phyllosphere microbial communities are limited. In this study, different stages of Pinus tabuliformis that were healthy or infected with B. xylophilus-associated leaf characteristics and phyllosphere bacterial and fungal communities were compared. These results demonstrated that soluble sugar and starch contents decreased based on the extent of infection. Phyllosphere microbial community changes potentially caused by B. xylophilus infection of P. tabuliformis and the fungal community compositions of healthy P. tabuliformis trees (Ya) were clearly different from diseased P. tabuliformis trees at an early stage of B. xylophilus infection (Yb) and P. tabuliformis trees in the last stage of B. xylophilus infection (Yc), particularly along the first coordinate axis. According to a linear discriminant effect size (LEfSe) analysis, the biomarker species in the phyllosphere of Yb were Acidobacteria, Deinococcus-Thermus, and Patescibacteria, while those in the phyllosphere of Ya were Proteobacteria, Aureobasidium, Dictyosporium, Alternariaster, Knufia, Microstroma, and Naganishia. Particularly at the end of PWD (pine wilt disease) infection, the majority of microbial taxa tended to co-exclude rather than co-occur with PWD infection. The result of a canonical correlation analysis (CCA) showed that the chemical properties of leaves, such as carbon and nitrogen, have significant impacts on phyllosphere microbial communities. These results expanded the possible connections between the phyllosphere communities and plant health.