Dinitrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the VAHINE mesocosm experiment (New Caledonia lagoon)
Dinitrogen fixation and dissolved organic nitrogen fueled primary production and particulate export during the VAHINE mesocosm experiment (New Caledonia lagoon)
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DOI：
10.5194/bg-12-4099-2015
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发表时间：
2015-01-01
期刊：
影响因子：
4.9
通讯作者：
Bonnet, S.
中科院分区：
文献类型：
--
作者：
Berthelot, H.;Moutin, T.;Bonnet, S.
在贫营养海洋中，表层沃茨中NO3-的耗竭是氮的重要来源，其中固定氮和溶解有机氮是氮的重要来源。在这项研究中，我们在新喀里多尼亚部署了大型原位围隔生态系统，以调查（1）N-2固定和DON使用对初级生产（PP）和颗粒输出的贡献，以及（2）新鲜产生的颗粒有机N（PON）的命运，即，无论它是优先在水柱中积累和再循环还是排出系统。在围隔中施用磷酸盐（PO 43-）以防止磷（P）限制并促进N-2固定。在实验的前10天（P1），固氮菌群落主要为固氮菌群，后9天（P2）为单细胞固氮蓝藻UCYN-C。在P1和P2期间，N2固定率平均值分别为9.8 +/- 4.0和27.7 +/- 8.6 nmol L-1 d（-1）。P1（9.0 +/-3.3%）和P2（12.6 +/-6.1%）期间的NO3-浓度（0.05）。然而，量化系统输出颗粒有机碳的效率的e比率（POCexport）与PP相比（e比率= POC输出/ PP）显著高于P2期间（p < 0.05）（39.7 +/-24.9%），而不是P1期间（23.9 +/-20.2%），表明UCYN-C维持的生产比DDAs维持的生产更有效地促进了C的出口。在P1期间，PON是稳定的，由N2固定提供的总N量（0.10 +/- 0.02 μ mol L-1）与输出的PON总量（0.10 +/- 0.04 μ mol L-1）没有显著差异（p > 0.05），这表明最近固定的N-2通过DDA快速且可能直接输出。在P2，PON浓度和PON出口增加了一个因素1.5-2的围隔。与P1不同的是，这种PON的产生不能完全由N-2固定提供的新N来解释。DON的浓度从5.3 +/- 0.5 μ mol L-1显著降低（p < 0.05）至4.4 +/- 0.5 μ mol L-1，其使用似乎是缺失的N源。P2期间DON的消耗量（约0.9 μ mol L ~（-1））高于同期固定N ~（-2）带来的新氮总量（约0.25 μ mol L ~（-1））。这些结果表明，虽然DDAs主要依赖于N-2固定的N需求，N-2固定和DON可以显着的N源初级生产和颗粒出口UCYN-C开花后，在新喀里多尼亚泻湖和扩展在N有限的海洋，类似的事件可能会发生。
In the oligotrophic ocean characterized by nitrate (NO3-) depletion in surface waters, dinitrogen (N-2) fixation and dissolved organic nitrogen (DON) can represent significant nitrogen (N) sources for the ecosystem. In this study, we deployed large in situ mesocosms in New Caledonia in order to investigate (1) the contribution of N-2 fixation and DON use to primary production (PP) and particle export and (2) the fate of the freshly produced particulate organic N (PON), i.e., whether it is preferentially accumulated and recycled in the water column or exported out of the system. The mesocosms were fertilized with phosphate (PO43-) in order to prevent phosphorus (P) limitation and promote N-2 fixation. The diazotrophic community was dominated by diatom-diazotroph associations (DDAs) during the first part of the experiment for 10 days (P1) followed by the unicellular N-2-fixing cyanobacteria UCYN-C for the last 9 days (P2) of the experiment. N2 fixation rates averaged 9.8 +/- 4.0 and 27.7 +/- 8.6 nmol L-1 d(-1) during P1 and P2, respectively. NO3- concentrations ( 0.05) during P1 (9.0 +/- 3.3 %) and P2 (12.6 +/- 6.1 %). However, the e ratio that quantifies the efficiency of a system to export particulate organic carbon (POCexport) compared to PP (e ratio = POCexport / PP) was significantly higher (p < 0.05) during P2 (39.7 +/- 24.9 %) than during P1 (23.9 +/- 20.2 %), indicating that the production sustained by UCYN-C was more efficient at promoting C export than the production sustained by DDAs. During P1, PON was stable and the total amount of N provided by N2 fixation (0.10 +/- 0.02 mu mol L-1) was not significantly different (p > 0.05) from the total amount of PON exported (0.10 +/- 0.04 mu mol L-1), suggesting a rapid and probably direct export of the recently fixed N-2 by the DDAs. During P2, both PON concentrations and PON export increased in the mesocosms by a factor 1.5-2. Unlike in P1, this PON production was not totally explained by the new N provided by N-2 fixation. The use of DON, whose concentrations decreased significantly (p < 0.05) from 5.3 +/- 0.5 mu mol L-1 to 4.4 +/- 0.5 mu mol L-1, appeared to be the missing N source. The DON consumption (similar to 0.9 mu mol L-1) during P2 is higher than the total amount of new N brought by N-2 fixation (similar to 0.25 mu mol L-1) during the same period. These results suggest that while DDAs mainly rely on N-2 fixation for their N requirements, both N-2 fixation and DON can be significant N sources for primary production and particulate export following UCYN-C blooms in the New Caledonia lagoon and by extension in the N-limited oceans where similar events are likely to occur.