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General Session 2: Marine & estuarine biogeochemistry |
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Enhancing and diminishing effects of light on uptake and oxidation of regenerated nitrogen
GS2-75-S
Min Xu* , State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Weijie Zhang, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Tao Huang, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Xiaolin Li, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Wenbin Zou, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Dawei Li, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Shuh-Ji Kao, State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
Presenter Email: minxu@stu.xmu.edu.cn
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| Light and nitrogen governs surface ocean productivity and the efficiency of marine biological pump. As a limiting nutrient for photosynthesis, nitrogen recycles rapidly in the surface ocean. Besides phytoplankton assimilation, oxidation is a competing pathway for regenerated nitrogen (i.e., ammonium (NH4+) and urea). Both pathways are sensitive to light, however, the quantitative information of their responses to light remains insufficient in the field. By using 15N labelled NH4+ and urea, both NH4+ and urea uptake and oxidation rates were determined under various levels of substrates and light in the western North Pacific. Here we showed light stimulates the assimilation of NH4+ and urea, while inhibits oxidation of both. Compared to urea, NH4+ associated rates are higher regardless of uptake and oxidation suggesting that NH4+ is recycled more rapidly than urea. Moreover, the kinetic responses of uptake and oxidation show that the maximal rate (Vmax) was controlled by biomass while half saturation constants (Km) positively correlate with ambient substrate concentrations. Light effects on Vmax and km were evaluated. Our finding suggested that light is the primary forcing to determine the dominant utilization pathway and turnover rates of regenerated nitrogen in the photic zone. Results benefit modeling works for nitrogen based biogeochemical model, from the perspective of light insolation and attenuation in water column (intensity and exposure period, e.g., diel cycle, seasonal daytime hours at different latitudes, particle-associated attenuation). |
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