Regulation of nitrous oxide production in low-oxygen waters off the coast of Peru

[摘要] Oxygen-deficient zones (ODZs) are major sites of net natural nitrous oxide ( N 2 O ) production and emissions. In order to understand changes in the magnitude of N 2 O production in response to global change, knowledge on the individual contributions of the major microbial pathways (nitrification and denitrification) to N 2 O production and their regulation is needed. In the ODZ in the coastal area off Peru, the sensitivity of N 2 O production to oxygen and organic matter was investigated using 15 N tracer experiments in combination with quantitative PCR (qPCR) and microarray analysis of total and active functional genes targeting archaeal amoA and nirS as marker genes for nitrification and denitrification, respectively. Denitrification was responsible for the highest N 2 O production with a mean of 8.7 nmol L −1  d −1 but up to 118±27.8  nmol L −1  d −1 just below the oxic–anoxic interface. The highest N 2 O production from ammonium oxidation (AO) of 0.16±0.003  nmol L −1  d −1 occurred in the upper oxycline at O 2 concentrations of 10–30  µ mol L −1 which coincided with the highest archaeal amoA transcripts/genes. Hybrid N 2 O formation (i.e., N 2 O with one N atom from NH 4 + and the other from other substrates such as NO 2 - ) was the dominant species, comprising 70 %–85 % of total produced N 2 O from NH 4 + , regardless of the ammonium oxidation rate or O 2 concentrations. Oxygen responses of N 2 O production varied with substrate, but production and yields were generally highest below 10  µ mol L −1   O 2 . Particulate organic matter additions increased N 2 O production by denitrification up to 5-fold, suggesting increased N 2 O production during times of high particulate organic matter export. High N 2 O yields of 2.1 % from AO were measured, but the overall contribution by AO to N 2 O production was still an order of magnitude lower than that of denitrification. Hence, these findings show that denitrification is the most important N 2 O production process in low-oxygen conditions fueled by organic carbon supply, which implies a positive feedback of the total oceanic N 2 O sources in response to increasing oceanic deoxygenation.

[学科分类] 大气科学