Natural grass coverage enriches arbuscular mycorrhizal fungal communities in subtropical citrus orchards through the regulation of Glomus on a regional scale

Arbuscular mycorrhizal (AM) fungi are ubiquitous soil fungi in orchard ecosystem, conferring a diverse array of benefits to citrus plants. However, how natural grass coverage, a common phenomenon in citrus orchards in southern China, shifts AM fungal communities in subtropical citrus orchards is far from being understood, especially on a regional scale, which impedes the understanding of the indigenous AM fungal adaptations. In this study, natural grass coverage rate, soil chemical properties, and soil AM fungal community in 80 sampling sites spanning 179, 700 km2 area in subtropical citrus orchards were investigated. The result of 18S rRNA gene highthroughput sequencing revealed that a total of eight AM fungal genera were identified and Glomus (90.15 %) was dominant genus in the community in citrus orchards. Natural grass coverage significantly increased soil organic matter (SOM), soil available phosphorus, and AM fungal alpha diversity, especially Glomus. Variation partitioning analysis revealed that grass coverage rate explained more variation in AM fungal alpha diversity than SOM. All the contrasting AM fungal species between different grass coverage rates and all the core AM fungal species belonged to Glomus. Null model analysis revealed that determinism played a slightly larger role in the assembly process of AM fungal communities than stochasticity with a distance-decay relationship. Moreover, natural grass coverage increased the relative importance of stochasticity in the community assembly. Taken together, these results suggest that maintaining natural grass coverage (naturally growing grass) is an effective nature-based solution for enriching AM fungal communities, which is essential for the sustainability of citrus production.