东印度洋次表层亚硝酸盐最大值的形成与维持机制

The primary nitrite maximum (PNM) located near the bottom of the euphotic layer in the stratified water column is generally observed in the tropic or subtropic seawater. The mechanisms inducing and sustaining the universal PNM have been extensively debated, ammoxidation or phytoplankton excretion? Based on the survey carried out in the two typical areas(N limitation/Fe limitation) in the East Indian Ocean, the formation mechanisms of the PNM will be explored. The aims are as follows: (1) to accurately measure nitrite production rates caused by ammonia oxidation(both ammonia-oxidizing bacteria and archaea) and phytoplankton excretion at different layers using 15N tracers and inhibitor technique in the shipboard incubations; (2) to determine the key environmental factors influencing the spatial and temporal variability of the PNM characteristics (e.g. depth, strength); (3) to quantitatively evaluate the contribution of ammonia oxidizer and phytoplankton to PNM formation and maintenance, respectively.The results can reveal the key driven step and their associated ecological effects of marine nitrogen cycle of the euphotic zone.

大洋层化水柱真光层底部亚硝酸最大值（PNM）形成和维持机制一直存在着争议。该现象是由氨氧化作用形成的，还是浮游植物释放导致的？印度洋次表层存在明显的PNM层，本项目以东印度洋典型区域（氮限制区和铁限制区）真光层亚硝酸盐为研究对象，利用15N同位素示踪技术、微生物抑制技术，准确测定不同水层氨氧化细菌、氨氧化古菌生产亚硝酸盐速率、浮游植物释放亚硝酸盐速率，以确定PNM层中亚硝酸盐的主要来源；研究PNM与环境因子的关系，揭示影响PNM深度、强度等特征的关键环境因素；对比分析氮限制区和铁限制区PNM层亚硝酸盐生产、累积的关键控制过程，量化氨氧化细菌、氨氧化古菌、浮游植物对PNM形成的相对贡献，阐明东印度洋PNM形成和维持的机制，为揭示大洋真光层氮循环的关键控制过程及其生态效应提供科学依据。

亚硝酸盐是硝化和反硝化过程的中间产物，其对海洋氮循环过程中氧化-还原途径之间的平衡具有重要的指示作用。本项目针对“亚硝酸盐最大值（PNM）形成和维持机制是由氨氧化作用形成的，还是浮游植物释放导致的？”这一科学问题。对东印度洋真光层底部亚硝酸盐累积的关键过程开展了一系列的研究，明确了PNM深度和强度，阐明了PNM层与硝酸盐跃层、次表层叶绿素最大值层等关键生化跃层相对位置的关系，探讨了浮游植物和微生物介导下水体亚硝酸盐的累积过程，阐述了氨氧化作用对PNM的贡献远高于浮游植物释放，揭示了氨氧化作用是水体PNM形成和维持的主控因素。研究结果明确了浮游植物和硝化微生物的相互作用调控着亚硝酸盐的循环过程，为阐释大洋水体氮循环关键过程、调控机制及其生态效应提供科学依据。

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