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The response of the marine nitrogen cycle to ocean acidification
Author(s) -
Wannicke Nicola,
Frey Claudia,
Law Cliff S.,
Voss Maren
Publication year - 2018
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.14424
Subject(s) - diazotroph , biogeochemical cycle , nitrogen cycle , nitrification , ecosystem , environmental science , ocean acidification , biogeochemistry , nitrogen , nitrogen fixation , cycling , denitrification , nutrient cycle , nutrient , ecology , environmental chemistry , mesocosm , carbon cycle , ammonium , marine ecosystem , biology , chemistry , climate change , history , organic chemistry , archaeology
Ocean acidification (OA), arising from the influx of anthropogenically generated carbon, poses a massive threat to the ocean ecosystems. Our knowledge of the effects of elevated anthropogenic CO 2 in marine waters and its effect on the performance of single species, trophic interactions, and ecosystems is increasing rapidly. However, our understanding of the biogeochemical cycling of nutrients such as nitrogen is less advanced and lacks a comprehensive overview of how these processes may change under OA. We conducted a systematic review and meta‐analysis of eight major nitrogen transformation processes incorporating 49 publications to synthesize current scientific understanding of the effect of OA on nitrogen cycling in the future ocean by 2100. The following points were identified by our meta‐analysis: (a) Diazotrophic nitrogen fixation is likely enhanced by 29% ± 4% under OA; (b) species‐ and strain‐specific responses of nitrogen fixers to OA were detectable, which may result in alterations in microbial community composition in the future ocean; (c) nitrification processes were reduced by a factor of 29% ± 10%; (d) declines in nitrification rates were not reflected by nitrifier abundance; and (e) contrasting results in unispecific culture experiments versus natural communities were apparent for nitrogen fixation and denitrification. The net effect of the nitrogen cycle process responses also suggests there may be a shift in the relative nitrogen pools, with excess ammonium originating from CO 2 ‐fertilized diazotrophs. This regenerated inorganic nitrogen may recycle in the upper water column increasing the relative importance of the ammonium‐fueled regenerated production. However, several feedback mechanisms with other chemical cycles, such as oxygen, and interaction with other climate change stressors may counteract these findings. Finally, our review highlights the shortcomings and gaps in current understanding of the potential changes in nitrogen cycling under future climate and emphasizes the need for further ecosystem studies.