Habitat heterogeneity drives arbuscular mycorrhizal fungi and shrub communities in karst ecosystems

Arbuscular mycorrhizal fungi (AMF) constitute one of the factors that regulate the success of vegetation restoration. Karst ecosystems are heterogenous in nutrient content and plant communities because of preferential water fluxes within cracks and gullies in the soil parent material. The effects of habitat on soil nutrients, shrub, and AMF diversity in karst ecosystems are yet to be established. Thus, we investigated the diversity of shrubs and AMF within three habitats: i) rocky soil surface (Rock), ii) soil surface (Soil), and iii) rocky gully (Gully) in a typical karst shrub ecosystem. We observed that AMF diversity was independent of the sampling location, whereas AMF abundance and the shrub Shannon index increased with sampling distance, reaching a plateau in a sampling area of 1000 m2. The AMF community composition was driven by dominating shrubs (Vitex negundo, Tirpitzia ovoidea). Higher shrub diversity and AMF abundance occurred in Rock than in Soil and Gully areas, suggesting higher habitat heterogeneity in Rock areas. Based on co-occurrence network analysis, interactions with a high link number among the AMF taxa were stronger in Rock than in Gully because the network complexity in the Rock areas strongly depended on symbiosis with AMF taxa to cope with high habitat heterogeneity. The Random forest model revealed that AMF abundance was mainly affected by available phosphorous, total potassium, and shrub diversity. Available phosphorous, soil pH, and exchangeable Ca2+, rather than plant diversity, were the main factor controlling AMF community composition. Overall, the results suggest that the increase in shrub diversity raised AMF abundance and richness, and strengthened the interactions among AMF taxa because of nutrient exchange. Thus, increasing habitat heterogeneity with abundant shrub diversity, but soil nutrient limitation, enriches AMF abundance and diversity.