Response of an Arctic Sediment Nitrogen Cycling Co

Authors: Karen Tait Bonnie Laverock Stephen Widdicombe

Publish Date: 2013/09/20

Volume: 37, Issue: 3, Pages: 724-735

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Abstract

Ocean acidification influences sediment/water nitrogen fluxes possibly by impacting on the microbial process of ammonia oxidation To investigate this further undisturbed sediment cores collected from Ny Alesund harbour Svalbard were incubated with seawater adjusted to CO2 concentrations of 380 540 760 1120 and 3000 µatm DNA and RNA were extracted from the sediment surface after 14 days exposure and the abundance of bacterial and archaeal ammonia oxidising amoA genes and transcripts quantified using quantitative polymerase chain reaction While there was no change to the abundance of bacterial amoA genes an increase to 760 µatm pCO2 reduced the abundance of bacterial amoA transcripts by 65  and this was accompanied by a shift in the composition of the active community In contrast archaeal amoA gene and transcript abundance both doubled at 3000 µatm with an increase in species richness also apparent This suggests that ammonia oxidising bacteria and archaea in marine sediments have different pH optima and the impact of elevated CO2 on N cycling may be dependent on the relative abundances of these two major microbial groups Further evidence of a shift in the balance of key N cycling groups was also evident the abundance of nirStype denitrifier transcripts decreased alongside bacterial amoA transcripts indicating that NO3 − produced by bacterial nitrification fuelled denitrification An increase in the abundance of Planctomycetespecific 16S rRNA the vast majority of which grouped with known anammox bacteria was also apparent at 3000 µatm pCO2 This could indicate a possible shift from coupled nitrification–denitrification to anammox activity at elevated CO2This work was funded by the European Project on Ocean Acidification EPOCA funded by the European Communitys Seventh Framework Programme FP7/20072013 under grant agreement no 211384 and was also supported by the NERC funded programme Oceans 2025 Theme 3 – Coastal and Shelf Processes BL acknowledges funding from an NERC Algorithm PhD Studentship NE/F008864/1 We thank Helen Findlay and Hannah Wood for setting up the mesocosm system Fred Gazeau Peter van Rijswijk Lara Pozzato MarieDominique Pizay and JeanPierre Gattuso for providing the carbonate and nutrient data Max Schwanitz Sandra Treydte and Julian Mönnich for collecting the sediment cores Vas Kitidis and Bess Ward for useful discussions and Paul Somerfield for advice on statistical analysesPhylogenetic tree of nirS transcripts from OTU data 80  similarity retrieved from the different pCO2 treatments filled triangle 81 filled square 77 filled circle 72 shown alongside previously reported environmental sequences The number of sequences derived from each pCO2 treatment is also shown for each OTU The tree topology is based on neighbourjoining and bootstrap analysis was performed with 1000 replications MEGA 5 The accession numbers of the reference sequences are shown in parentheses JPEG 606 kb

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