Objective Chemical fertilizers are often over applied in citrus orchards for high fruit yield. Citrus is mycorrhiza - dependent plants, has relatively few root hairs, so requiring assistance from microorganism for sufficient nutrient absorption. Therefore, we studied the effects of fertilization practices on the community structure,diversity, and co-occurrence network patterns of arbuscular mycorrhizal fungi (AMF)in citrus soil.

Methods The research choosed 24 citrus orchards in Quzhou City, Zhejiang Province, including 5 orchards without fertilizer application (NF), 10 orchards only applying chemical fertilizer (CF), and 9 orchards with co-application of chemical and organic fertilizers (COF). Soil samples were collected in the orchards, and the wet-screened decanting-sucrose centrifugation method was used to determine AM fungi spore density, the high-throughput sequencing technique was used for analysis of soil AM fungal community.

Results Compared to NF orchards, COF significantly increased the fruit Vc and solid acid contents by 22.1% and 65.5%, enhanced soil organic carbon, total N, and available NPK contents. Neither COF nor CF changed soil pH, easily extractable glomalin, and AM fungal spore density significantly. The dominant genera of soil AM fungi were Funneliformis, Glomus, and Rhizophagus. Compared to NF, CF and COF decreased the relative abundance (RA) of Funneliformis but increased that of Rhizophagus significantly. The RA of Rhizophagus was positively correlated with soil organic carbon, and available K contents, positively correlated with fruit Vc content and solid-acid ratio. The RA of Glomus and Funneliformis negatively correlated with soil organic carbon, and available Kcontents. However, Compared to NF, CF and COF did not affect on the Shannon and Simpson indices of AM fungal community, but decreased AM fungal richness (Chao1 index) and changed the community structure significantly. Fertilization changed the Co-occurrence network patterns of AM fungi, and the network under NF treatment being the most stable.

Conclusion Fertilization significantly altered soil AM fungal community structures and changed their relative abundances at genus level through modifying soil organic carbon and available K content, consequently declined the complexity and stability of AM fungal community networks. The co-application of organic and chemical fertilizers significantly improved the fruit quality of citrus, and soil nutrient content and the relative RA of Rhizophagus due to high soil organic carbon and available K, and the high spore density.