Microbial roles in reconstructive restoration: Divergence in soil microbiomes from constructed and natural tree islands mediate tree growth under hydrological stress

As ecosystems face unprecedented change and habitat loss, pursuing comprehensive and resilient habitat restoration will be integral to protecting and maintaining natural areas and the services they provide. Microbiomes offer an important avenue for improving restoration efforts as these hidden players are integral to ecosystem health and functioning. Despite microbiomes importance, unresolved knowledge gaps hinder their inclusion in restoration efforts. Here, we address two critical gaps in understanding microbial roles in restoration, microbiomes importance in reconstructive restoration efforts and how management and restoration decisions interactively impact microbial communities and their cascading effects on plants, the primary producers that fuel natural communities. We combined field surveys, microbiome sequencing, and greenhouse experiments to determine how reconstructing an iconic landscape feature (tree islands) in the Everglades impacts microbiomes and microbial effects on native tree species compared to their natural microbial counterparts under different possible hydrological management regimes. We found that while fungal microbiomes from natural and constructed tree islands exhibited similar diversity and richness, they differed significantly in fungal community composition. These compositional differences arose mainly from changes to which microbial taxa were present on the islands rather than changes in relative abundances. Surprisingly, around 50 percent of microbial hub taxa (putative keystone fungi) from natural islands were completely missing on constructed islands, suggesting that differences in community composition of constructed island could be important for microbiome stability and function. The differences in microbial composition between natural and constructed islands did have important consequences for native tree growth. Specifically, these compositional differences interacted with hydrological regime (treatments simulating management strategies) to affect woody growth across the four tree species in our experiment. Our results suggest that reconstructing a landscape feature tree without consideration of microbiomes can result in diverging microbial communities that are likely to interact with water management decisions leading to meaningful consequences for foundational primary producers.