Though the effects of anthropogenic disturbances on coastal marsh plant communities have been extensively studied, root-associated soil microbiota responses to severe disturbance are not well understood. Over 1000 miles of shoreline across the northern Gulf of Mexico were oiled as a result of the 2010 Deepwater Horizon spill, with the Louisiana coast sustaining the heaviest oiling. In previous work, we found that oil exposure shifted the community composition of endophytes in Louisiana salt marshes. Other studies have similarly found that oil exposure affects salt marsh soil microbiota, but it is not clear whether exposure elicits parallel responses in root-associated microbiota. It is also not known how responses progress over time.
We examined how the diversity of soil microbiota associated with Spartina alterniflora roots changed at a lightly oiled (Fourchon) and a heavily oiled (Bay Jimmy) salt marsh site in southern Louisiana, beginning approximately two years after the oil spill. We sampled three transects at the Fourchon site over 17 months and 22 plots at the Bay Jimmy site over 11 months. Using the Illumina HiSeq platform, we sequenced from the V4 region of the 16S rDNA to profile root-associated bacterial communities in samples taken from the sites.
Results/Conclusions
We found the microbial communities of Fourchon and Bay Jimmy to be significantly different. At each site the community significantly varied with season as well. Bacterial communities showed significant compositional changes along oiling gradients at both sites. The differences between site and seasonal patterns at each site may be attributable to differences in oiling sustained at each site. Other factors, such as plant genotype, might be contributing to observed differences within and among our study sites. Future work will investigate relationships between root-associated soil microbiota, bacterial and fungal endophytes, plant genotype, and environmental conditions.