Ocean Acidification Experiments in Large-Scale Mesocosms Reveal Similar Dynamics of Dissolved Organic Matter Production and Biotransformation
Ocean Acidification Experiments in Large-Scale Mesocosms Reveal Similar Dynamics of Dissolved Organic Matter Production and Biotransformation
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DOI：
10.3389/fmars.2017.00271
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发表时间：
2017-09
影响因子：
3.7
通讯作者：
Maren Zark;Nadine K. Broda;T. Hornick;H. Grossart;U. Riebesell;T. Dittmar
中科院分区：
文献类型：
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作者：
Maren Zark;Nadine K. Broda;T. Hornick;H. Grossart;U. Riebesell;T. Dittmar
溶解有机物（DOM）是海洋中碳的主要储存库。海洋酸化等环境压力因素可能会影响DOM的产生和降解过程，例如浮游植物渗出或微生物吸收和分子的生物转化。因此，海洋碳储存能力的变化可能会对全球碳循环产生反馈。然而，以往的实验研究OA对DOM库在自然条件下的影响，主要是在温带和沿海富营养化地区进行。在这里，我们报告OA对现有的和新产生的DOM池在实验中在亚热带北大西洋加那利群岛在（1）贫营养阶段和（2）模拟深水上升流。最后一个是该地区经常发生的事件，控制营养盐和浮游植物动态。我们操作了9个大规模围隔生态系统，pCO 2梯度范围为~350至~1030 µatm，并通过傅里叶变换离子回旋共振质谱法（FT-ICR-MS）使用超高分辨率质谱法监测DOM分子组成。在模拟上升流引起的浮游植物水华期间，在所有围隔中观察到37 µmol L-1 DOC的增加。在实验结束时，营养物循环的一个阶段，在CO2浓度升高的情况下，DOC积累增强的迹象变得明显。DOM的产生反映在DOM分子组成的变化上。在整个实验过程中检测到的7，212种分子式中，约50%的质谱信号强度与累积的细菌蛋白质产量显著相关，并且可能是微生物转化的产物。然而，没有发现所产生的化合物在CO2水平方面的差异。比较这个实验的结果，在瑞典Gullmar峡湾的一个可比的OA实验，揭示了类似的演替模式，个别化合物池在浮游植物水华和随后的积累，这些化合物进行了观察。类似的行为DOM生产和生物转化过程中和之后的浮游植物水华，无论浮游生物群落组成和CO2处理提供了新的见解海洋DOM池的一般动态。
Dissolved organic matter (DOM) represents a major reservoir of carbon in the oceans. Environmental stressors such as ocean acidification (OA) potentially affect DOM production and degradation processes, e.g. phytoplankton exudation or microbial uptake and biotransformation of molecules. Resulting changes in carbon storage capacity of the ocean, thus, may cause feedbacks on the global carbon cycle. Previous experiments studying OA effects on the DOM pool under natural conditions, however, were mostly conducted in temperate and coastal eutrophic areas. Here, we report on OA effects on the existing and newly produced DOM pool during an experiment in the subtropical North Atlantic Ocean at the Canary Islands during an (1) oligotrophic phase and (2) after simulated deep water upwelling. The last is a frequently occurring event in this region controlling nutrient and phytoplankton dynamics. We manipulated nine large-scale mesocosms with a gradient of pCO2 ranging from ~350 up to ~1030 µatm and monitored the DOM molecular composition using ultrahigh-resolution mass spectrometry via Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). An increase of 37 µmol L-1 DOC was observed in all mesocosms during a phytoplankton bloom induced by simulated upwelling. Indications for enhanced DOC accumulation under elevated CO2 became apparent during a phase of nutrient recycling towards the end of the experiment. The production of DOM was reflected in changes of the molecular DOM composition. Out of the 7,212 molecular formulae, which were detected throughout the experiment, ~50% correlated significantly in mass spectrometric signal intensity with cumulative bacterial protein production and are likely a product of microbial transformation. However, no differences in the produced compounds were found with respect to CO2 levels. Comparing the results of this experiment with a comparable OA experiment in the Swedish Gullmar Fjord, reveals similar succession patterns for individual compound pools during a phytoplankton bloom and subsequent accumulation of these compounds were observed. The similar behavior of DOM production and biotransformation during and following a phytoplankton bloom irrespective of plankton community composition and CO2 treatment provides novel insights into general dynamics of the marine DOM pool.