Abstract: The aim of this study was to explore the relationship between the leaf nutrient elements and leaf surface community structure under different citrus moss degrees. In this study, we collected the leaves of W·murcott from two different citrus orchards in Jiangjin district of Chongqing for experiments. The degree of leaf moss was classified into G0-G5 and the disease index was counted. Also, the nutrient element content of nitrogen (N), phosphorus (P), potassium (K), calcium(Ca), magnesium(Mg), zinc(Zn), copper(Cu), iron(Fe), manganese(Mn), boron (B) in the leaves of each disease level was determined. High-throughput sequencing technology was utilized to explore the community composition, abundance, difference of phyllosphere eukaryotes under different disease levels. The results showed that both of the severity and characteristics of citrus moss in the two orchards were similar. The content of P was significantly negatively correlated with disease severities, the content of Mg was significantly negatively correlated with disease severities, and the content of Ca was significantly positively correlated with disease severities, the content of K was significantly positively correlated with disease severities. At the genus level, the dominants in G1 were Heterochlorella, Sporidiobolus and Cladosporium, the dominants in G2 were Heterochlorella, Symmetrospora and Microsporomyces, the dominants in G3 were Heterochlorella, Cladosporium and Sporidiobolus, the dominants in G4 were Heterochlorella, Cladosporium and Heveochlorella, and the dominants in G5 were Heterochlorella, Cladosporium and Microsporomyces. The relative abundance of uncultured Apatococcus, Cladosporium herbarum, Heveochlorella hainangensis on leaf surface were positively correlated with the disease levels. The content of P, Fe, Mg, Mn, Cu, N had a great influence on the structure of leaf biota species. The main pathogen uncultured Apatococcus, Cladosporium herbarum were negatively correlated with the content of P and they were positively correlated with Ca. Investigating relationship between mineral nutrient elements in citrus leaves and the eukaryotic community structure of leaf surface, we found the P content was significantly negatively correlated with citrus moss severities and the relative abundance of the major pathogens, the Ca content in the leaves were positively correlated with the citrus moss disease levels and the relative abundance of the main pathogens. In conclusion, citrus moss was most closely related to P and Ca in leaves, and the occurrence degree of citrus moss can directly affect the content of P and Ca in leaves.

Key words: citrus, moss, mineral nutrient element, eukaryote, disease grade