Functional Diversity of Plant Communities Explains the Response of Soil Microbes to Plant Invasion Along a Successional Gradient

Ecosystems worldwide face growing impacts from non-native species invasions. However, little is known about how soil microbial communities respond to the addition of non-native plants, and whether these responses differ along a successional gradient. To address these knowledge gaps, we collected soil samples, recorded plant species cover and measured the traits of the plant species in lava flow vegetation and lowland rainforest (representing early and late successional stages) on La Réunion Island. Our results show that non-native plant cover drives variation in plant species diversity, community composition, functional composition (community-weighted means of vegetative height and leaf area) and functional diversity (mean pairwise trait distance among species), with these effects being stronger in early than in late successional stage. Non-native plant cover did not affect the diversity or community composition of soil fungi and bacteria. Instead, the functional diversity of plant communities associated with non-native plant addition explained the variation in soil microbial community composition and co-occurrence network structure. These results suggest that while non-native plant cover is a good indicator of variation in plant community composition, the functional diversity of the plant community is more useful for describing shifts in soil microbial communities of invaded habitats along primary succession.