Plant Microbiomes

Salt marsh ecosystems are dominated by the smooth cordgrass Spartina alterniflora on the US Atlantic and Gulf of Mexico coastlines. Although soil microorganisms are well known to mediate important biogeochemical cycles in salt marshes, little is known about the role of root microbiomes in supporting the health and productivity of marsh plant hosts. We investigate the relationships between S. alterniflora primary productivity, sediment redox potential, and the physiological ecology of bulk sediment, rhizosphere, and root microbial communities at Georgia barrier islands.

We have found that the S. alterniflora root microbiome is dominated by highly active and competitive species taking advantage of available carbon substrates in the oxidized root zone. We have proposed two microbially-mediated mechanisms that we thought stimulate S. alterniflora primary productivity:

1. Enhanced microbial activity replenishes nutrients and terminal electron acceptors in higher biomass stands.
2. Coupling of chemolithotrophic S oxidation with carbon (C) and nitrogen (N) fixation by root and rhizosphere associated prokaryotes. Sulfur oxidizing bacteria detoxify sulfide in the root zone while potentially transferring fixed C and N to the host plant. This relationship resembles that of the previously discovered symbiosis between marine benthic invertebrates and sulfur oxidizing bacteria.