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AME prepress abstract   -  DOI: https://doi.org/10.3354/ame01954

Nitrogen cycling in coastal sediment microbial communities with seasonally variable benthic nutrient fluxes

Alexis J. Marshall, Andrew Longmore, Lori Phillips, Caixian Tang, Helen L. Hayden, Karla B. Heidelberg, Pauline Mele

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ABSTRACT: Benthic microbial communities contribute to nitrogen (N) cycling in coastal ecosystems through taxon specific processes such as anammox, nitrification and N-fixation and community attributed pathways such as denitrification. By measuring the total (DNA-based) and active (RNA-based) surface sediment microbial community composition and the abundance and activity profiles of key N-cycling genes in a semi-enclosed embayment—Port Phillip Bay (PPB), Australia—we show that although the total relative abundance of N-cycling taxa is comparatively lower close to estuary inputs (Hobsons Bay; HB), the capacity for this community to perform diverse N-cycling processes is comparatively higher than in sediments isolated from inputs (Central PPB ; CPPB). In HB, seasonal structuring of the sediment microbial community occurred between spring and summer, co-occurring with decreases in the activity profiles of anammox bacteria and organic carbon content. No changes were detected in the activity profiles of nitrifiers or the community-based pathway denitrification. Although no seasonal structuring of the sediment microbial community occurred in CPPB, the activity profiles of key N-cycling genes displayed comparatively higher within-site variability. These results show that despite N-cycling taxa representing a smaller fraction of the total community composition in estuary impacted sediments (HB), these microbial communities consistently engage in N-cycling processes and that seasonal instability in the composition of this community is not reflective of changes in its capacity to cycle N through coupled nitrification-denitrification but potentially via changes within the anammox community.