Dynamics of N2 fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)
Dynamics of N2 fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)
复制标题
DOI：
10.5194/bg-13-2653-2016
复制
发表时间：
2016-01-01
期刊：
影响因子：
4.9
通讯作者：
Berman-Frank, Ilana
中科院分区：
文献类型：
--
作者：
Bonnet, Sophie;Berthelot, Hugo;Berman-Frank, Ilana
在热带西南太平洋沿海（新喀里多尼亚）部署的大型（类似于50 m3）围隔生态系统中，每天测量N-2固定率，以研究N-2固定率与环境参数的时间变化，并研究低营养、低叶绿素生态系统中重氮营养源氮（DDN）的归宿。的中生态系统施肥与类似的0.8 μ M溶解无机磷（DIP），以刺激固氮。整体N-2固定率在三个围隔生态系统之间是可复制的，在23天内平均为18.5 +/- 1.1 nmol N L-1 d（-1），在实验的后半段（第15至23天）增加了2倍，达到27.3 +/- 1.0 nmol N L-1 d（-1）。在DIP施肥后测得的这些后期速率高于全球海洋报告的上限。在23 d的实验中，N-2固定率与海水温度、初级生产力、细菌生产力、颗粒有机碳（POC）、氮（PON）和磷（POP）现存量以及碱性磷酸酶活性呈正相关，与DIP浓度、DIP周转时间、硝酸盐、溶解性有机氮和磷浓度呈负相关。DDN的命运进行了研究，在开花的单细胞固氮菌UCYN-C，发生在实验的后半部分。沉积物捕集器中固氮生物的定量表明，每天从水柱中输出的UCYN-C接近10%，占UCYN-C水华高峰时输出的总POC的22.4 +/-5.5%。这种输出主要是由于小的（5.7 +/- 0.8 μ m）UCYN-C细胞聚集成大的（100-500 μ m）聚集体。在同一时间段，基于高分辨率纳米尺度二次离子质谱的DDN转移实验（nanoSIMS）结合N-15（2）同位素标记显示，16 +/-6%的DDN被释放到溶解池中，21 +/-4%被转移到非重氮营养浮游生物中，主要是微型浮游生物（18 +/-4%），其次是硅藻（3 +/-2%）。这是与观察到的急剧增加的微型浮游生物和硅藻丰度，初级生产，细菌生产，和常设股票的POC，PON和持久性有机污染物在实验的后半部分的中围生态系统。这些结果提供了深入了解DDN的命运在开花的UCYN-C在低营养，低叶绿素的生态系统。
N-2 fixation rates were measured daily in large (similar to 50 m(3)) mesocosms deployed in the tropical southwest Pacific coastal ocean (New Caledonia) to investigate the temporal variability in N-2 fixation rates in relation with environmental parameters and study the fate of diazotrophderived nitrogen (DDN) in a low-nutrient, low-chlorophyll ecosystem. The mesocosms were fertilized with similar to 0.8 mu M dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. Bulk N-2 fixation rates were replicable between the three mesocosms, averaged 18.5 +/- 1.1 nmol N L-1 d(-1) over the 23 days, and increased by a factor of 2 during the second half of the experiment (days 15 to 23) to reach 27.3 +/- 1.0 nmol N L-1 d(-1). These later rates measured after the DIP fertilization are higher than the upper range reported for the global ocean. During the 23 days of the experiment, N-2 fixation rates were positively correlated with seawater temperature, primary production, bacterial production, standing stocks of particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP), and alkaline phosphatase activity, and negatively correlated with DIP concen-trations, DIP turnover time, nitrate, and dissolved organic nitrogen and phosphorus concentrations. The fate of DDN was investigated during a bloom of the unicellular diazotroph UCYN-C that occurred during the second half of the experiment. Quantification of diazotrophs in the sediment traps indicates that similar to 10 % of UCYN-C from the water column was exported daily to the traps, representing as much as 22.4 +/- 5.5 % of the total POC exported at the height of the UCYN-C bloom. This export was mainly due to the aggregation of small (5.7 +/- 0.8 mu m) UCYN-C cells into large (100-500 mu m) aggregates. During the same time period, a DDN transfer experiment based on high-resolution nanometerscale secondary ion mass spectrometry (nanoSIMS) coupled with N-15(2) isotopic labeling revealed that 16 +/- 6 % of the DDN was released to the dissolved pool and 21 +/- 4 % was transferred to non-diazotrophic plankton, mainly picoplankton (18 +/- 4 %) followed by diatoms (3 +/- 2 %). This is consistent with the observed dramatic increase in picoplankton and diatom abundances, primary production, bacterial production, and standing stocks of POC, PON, and POP in the mesocosms during the second half of the experiment. These results offer insights into the fate of DDN during a bloom of UCYN-C in low-nutrient, low-chlorophyll ecosystems.