| |
| |
|
|
|
|
| |
 |
Nitrogen cycling in the ocean: From genes to ecosystems and from the past to the future
|
| |
|
|
Surface nitrification and its climatic effect in oligotrophic ocean
Monday 7th @ 1050-1110, Multifunction Hall
Xianhui Wan* , State Key Laboratory of Marine Environmental Science, Xiamen University
Hua-Xia Sheng, State Key Laboratory of Marine Environmental Science, Xiamen University
Minhan Dai, State Key Laboratory of Marine Environmental Science, Xiamen University
Yao Zhang, State Key Laboratory of Marine Environmental Science, Xiamen University
Dalin Shi, State Key Laboratory of Marine Environmental Science, Xiamen University
Shuh-Ji Kao, State Key Laboratory of Marine Environmental Science, Xiamen University
Presenter Email: wanxh@xmu.edu.cn |
| The supply and cycling of nitrogen play an essential role in regulating ocean's ability in absorbing atmospheric carbon dioxide (CO2) and releasing nitrous oxide (N2O). In oligotrophic ocean, the primary production and its subsequent exporting (termed as biological pump) is largely limited by nitrogen, competition of nitrogen by phytoplankton and microbe thus determines the flow of nitrogen towards driving CO2 uptake or N2O production. By investigating the competition of ammonium by phytoplankton and ammonia oxidizers and measuring the N2O production rate in the oligotrophic South China Sea and subtropical Western Pacific, we find that ambient nitrate acts as a key variable to bifurcate ammonium flow through assimilation or oxidation, and the depth of the nitracline represents a robust spatial boundary between ammonium assimilators and oxidizers in the stratified ocean. Phytoplankton assemblages in nitrate depleted regimes have higher ammonium affinity than nitrifiers. In nitrate replete conditions, by contrast, phytoplankton reduce their ammonium reliance and thus enhance the success of nitrifiers. Accordingly, active N2O production is observed below the nitracline and peaked at the base of euphotic zone. These findings demonstrate that the intimate coupling of carbon and nitrogen cycling in the upper ocean not only act as a CO2 sink but also a N2O source. Therefore, the offset of CO2 absorbing by N2O production must be considered in future study to a reach comprehensive understanding of the role of ocean in Earth's climate. |
|
|
|
|
|
|
|
|