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Poster Number:
128
Presenter/Primary Author:
Patrick Kearns Salt marshes are highly productive ecosystems that provide numerous ecosystem services.
Despite their importance, salt marshes have experienced substantial declines in recent
decades, partly due to excess anthropogenic nitrogen additions. Salt marshes harbor
abundant, highly diverse, and active microbial communities, but we have a poor
understanding of how they respond to changes in their environment, in particular to nutrient
enrichment. To address this knowledge gap, we examined sediment microbial communities
from four creeks nested within a decade-long marsh fertilization experiment as part of the
TIDE project at the Plum Island Ecosystems LTER during 2005-2006 and 2013-2014. We
sampled sediment underlying the dominant macrophytes (tall Spartina alterniflora and
Spartina patens) monthly over the course of the growing season (May-October) and
sequenced both 16S rDNA and 16S rRNA to analyze the total (16S rDNA) and active (16S
rRNA) microbial communities. When examining the total microbial communities, we observed
no effect of fertilization, while a strong effect of habitat was evident. Analysis of 16S rRNA,
however, revealed a dramatic effect of fertilization on the active microbial communities. The
active communities in the unfertilized sediments were strongly structured by both season and
plant type, while no such patterns existed in the fertilized sediments suggesting a
homogenization of the active microbial communities. Additionally, active communities in the
fertilized sediments from 2013 and 2014 showed distinct compositions from corresponding
communities in 2005 and 2006, suggesting long-term effects of fertilization on active
microbes. Our results suggest fertilization elicits a homogenization effect on microbial
communities, overwhelming the effects of season and habitat observed in unfertilized
sediments and reducing overall microbial diversity.
Student Poster Competition:
Yes 
