New Insights Into the Influence of Plant and Microbial Diversity on Denitrification Rates in a Salt Marsh

Coastal salt marshes are some of the most productive ecosystems on Earth, providing numerous services such as soil carbon storage, flood protection and nutrient filtering, several of which are mediated by the sediment microbiome associated with marsh vegetation. Here, nutrient filtering (nitrate removal through denitrification) was examined by determining microbial (bacteria and archaea) community structure (16S rRNA gene iTag sequencing), diversity, denitrification rates and metabolic potential (assembled metagenomic sequences) in collocated patches of Spartina alterniflora (Spartina) and Juncus roemerianus (Juncus) sediments. The iTag data showed that diversity and richness in Spartina and Juncus sediment microbial communities were highly similar. However, microbial community evenness differed significantly, with the most even communities observed in Juncus sediments. Further, denitrification rates were significantly higher in Juncus compared to Spartina, suggesting oscillations in microbial abundances and in particular the core microbiome identified herein, along with plant diversity influence marsh nitrogen (N) removal. Amplicon and assembled metagenome sequences pointed to a potentially important, yet unappreciated Planctomycetes role in N removal in the salt marsh. Thus, ecosystem perturbations that alter marsh vegetation distribution could impact microbial diversity and may ultimately influence the ecologically important ecosystem functions the marsh sediment microbiome provides.

Automated summary

Coastal salt marshes are highly productive ecosystems that provide essential services such as soil carbon storage, flood protection, and nutrient filtering. This study examined nutrient filtering in marsh sediments by analyzing microbial community structure, diversity, denitrification rates, and metabolic potential in different vegetation patches. The results showed that microbial communities in Spartina and Juncus sediments had similar diversity and richness, but differed in evenness, with Juncus sediments having the most even communities. Additionally, denitrification rates were higher in Juncus sediments, indicating that microbial abundances and the core microbiome may play a role in marsh nitrogen removal. Sequencing data suggested a potentially important role of Planctomycetes in nitrogen removal in salt marshes. Ecosystem perturbations that affect marsh vegetation distribution could impact microbial diversity and ecosystem functions.