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General Session 3: Biological oceanography & global change |
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Inverse temperature effect on rate measure for nitrifier community in the South China Sea
GS3-73-S
Zhenzhen Zheng* , Xiamen University
Shuh-Ji Kao, Xiamen University
Presenter Email: zhengzz@stu.xmu.edu.cn
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| Nitrification, a central recycling pathway in nitrogen cycle, produces greenhouse gas (nitrous oxide) as a by-product, thus can act as a feedback to climate change. However, how oceanic nitrification responds to temperature change under global warming scenario remains debatable. In this study, we conducted a temperature manipulation experiment in South China Sea, where the substrate (NH4+) is limited for nitrifier. By using isotope labelling technique, we aimed to explore the temperature effect on nitrification rate and nitrifier community in the field. Counterintuitively, we found nitrification rates declined significantly as warming and increased as cooling. Such results violate Arrhenius theory. By analyzing transformation pathways in detail by modeling practices, we excluded all plausible causes included: 1) greater ammonium competition from phytoplankton or phytobacteria in higher temperature condition, 2) biased estimates due to warming, which enhanced both remineralization (dilution of 15N tracer) and consumption of NOx- (product of nitrification) by phytoplankton or phytobacteria. Previous studies for the temperature sensitivity of the soil carbon decomposition showed that both maximum reaction (Vmax) and half-saturation constant (Km) were sensitive to temperature yet to various degrees. Due to the low substrate concentration in our case, we hypothesize that negative temperature effect is attributed to deviated responses of Km and Vmax to temperature change. Collectively, our results suggest that global warming could reduce nitrification rates in the open ocean where the ammonium concentrations are low, a negative feedback to climate change thus may happen due to reduction of nitrous oxide production via nitrification. |
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