工业革命以来，人类活动导致大气CO2的浓度上升了约40%。对于海洋初级生产者浮游植物而言，大气CO2水平的升高对其造成的影响将是多方位的。首先，温室效应将导致海水层化加剧，一方面减弱营养盐（如，硝酸盐）从深层海水向表层海水的输入，另一方面使得浮游植物所接受的平均光强增加。其次，在造成海水暖化的同时，大量CO2溶解在表层海水中引起海洋酸化，由此改变的海水碳酸盐体系不仅将对浮游植物的光合固碳产生影响，而且可能影响浮游植物氮营养的结构，例如，已有研究表明海水酸化会抑制硝化作用，从而改变海水中铵盐和硝酸盐的比例。
阐明海洋浮游植物在全球变化多因子协同作用下的响应及其机制，对深入理解全球变化对海洋生态系统的影响有着重要的意义。然而，准确评估并预测相互关联的多个环境因子对浮游植物生长及光合作用的净效应，具有相当的挑战性。因为，生物多样性、生态水平的相互作用以及进化动力学等因素，均可能影响浮游植物对环境变化的响应。迄今，应对上述挑战的研究方法主要包括了，聚焦于某个功能群、选择代表性的关键种或模式种、应用综合模型等。然而，这些手段均存在各自的优点和不足。
运用能量和限制性资源的收支平衡评估环境变化对某一物种的影响，在生态学上有着较为广泛的应用。然而，在全球变化对海洋浮游系统，特别是多环境因子的耦合对浮游植物个体的影响方面，该手段的应用尚十分有限。史大林课题组从藻类的能量代谢角度出发，以假微海链藻（Thalassiosira pseudonana）作为模式生物，运用生理、生化和分子生物学等方法，系统、定量地分析了藻类细胞中与能量的捕获、代谢、储存相关的各关键过程对光照、氮源以及CO2条件改变的响应。研究发现，假微海链藻在高光条件下提高了光的捕获速率、在氨盐条件下增加了光合蛋白的表达，从而促进了细胞光合能量的产生；随后，藻类通过对CO2浓缩机制、卡尔文循环、光呼吸以及硝酸盐还原等代谢过程中能量分配、利用与储存的调控，以应对光能的变化。有趣的是，CO2的上升抑制了假微海链藻对硝酸盐的吸收和利用，表现为硝酸还原酶基因的转录水平、蛋白表达及活性在高CO2条件下系统性的下调。细胞内能量代谢的改变最终引起细胞生化组成、碳氮比以及溶解性有机物的释放等变化，这将对海洋生态系统中的能量传递和食物链效应产生一定影响。在实验基础上，史大林课题组首次建立了一个能量收支模型，较为准确的预测了上述多因子环境变化将如何影响浮游植物的光合作用。这为科学推测海洋生态系统对全球变化的响应提供了一个新的有效手段。
该成果于2015年7月7日在线发表于《Limnology and Oceanography》上： Dalin Shi*, Weiying Li, Brian M. Hopkinson, Haizheng Hong, Dongmei Li Shuh-Ji Kao and Wenfang Lin. Interactive effects of light, nitrogen source, and carbon dioxide on energy metabolism in the diatom Thalassiosira pseudonana. 2015 Limnology and Oceanography, doi: 10.1002/lno.10134.
Abstract: Due to the ongoing effects of climate change, phytoplankton are likely to experience enhanced irradiance, more reduced nitrogen, and increased water acidity in the future ocean. Here, we used Thalassiosira pseudonana as a model organism to examine how phytoplankton adjust energy production and expenditure to cope with these multiple, interrelated environmental factors. Following acclimation to a matrix of irradiance, nitrogen source, and CO2 levels, the diatom's energy production and expenditures were quantified and incorporated into an energetic budget to predict how photosynthesis was affected by growth conditions. Increased light intensity and a shift from to led to increased energy generation, through higher rates of light capture at high light and greater investment in photosynthetic proteins when grown on . Secondary energetic expenditures were adjusted modestly at different culture conditions, except that utilization was systematically reduced by increasing pCO2. The subsequent changes in element stoichiometry, biochemical composition, and release of dissolved organic compounds may have important implications for marine biogeochemical cycles. The predicted effects of changing environmental conditions on photosynthesis, made using an energetic budget, were in good agreement with observations at low light, when energy is clearly limiting, but the energetic budget over-predicts the response to at high light, which might be due to relief of energetic limitations and/or increased percentage of inactive photosystem II at high light. Taken together, our study demonstrates that energetic budgets offered significant insight into the response of phytoplankton energy metabolism to the changing environment and did a reasonable job predicting them.
Link to Full article: http://onlinelibrary.wiley.com/doi/10.1002/lno.10134/abstract
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