Planting Spartina alterniflora in a salt marsh denuded of vegetation by an oil spill induces a rapid response in the soil microbial community

The need for a comprehensive understanding of coastal wetland restoration strategies became clear following the Deepwater Horizon oil spill when quantities of oil reaching the marshes overwhelmed the ecosystem's natural attenuation capacity for several years in the worst-hit areas. Planting and fertilization are common habitat restoration methods in wetlands, but how these treatments impact the native soil microbial community when implemented in formerly oiled salt marshes is not well understood. This research used DNA sequencing to determine how the soil microbial community changed in response to planting, fertilization, and their interaction, and how environmental variables were related to the soil microbial community structure. We studied a salt marsh in northern Barataria Bay, Louisiana, USA that had not revegetated four years after the Deepwater Horizon oil spill using factorial combinations of Spartina alterniflora transplants and biannual fertilizer applications. Transplants significantly affected the soil microbial community structure during the first 13 months after initiating treatment. A cohort of putative sulfate-reducing bacteria (SRB) were significantly more abundant in the transplanted treatments than in the unplanted treatments after 13 months. The response of the microbial community to fertilizer depended on the presence or absence of transplants during that time. Fertilizer application in the absence of transplants resulted in a proliferation of a Staphylococcus taxon after two months, a significant increase in community heterogeneity after 7 months, and a shift in community composition after 13 months, but fertilizer application had no apparent effect on the soil microbial community in combination with S. alterniflora transplants. These results suggest that transplanted S. alterniflora promotes a rapid shift in the soil microbial community composition with concurrent establishment of a diverse community of SRB and mediates the effect of fertilizer on the soil microbial community in previously oiled salt marsh systems. The rapid response by the microbial community to revegetation suggests that planting S. alterniflora will hasten habitat restoration following future oil spills.