利用15N同位素探究浒苔对不同形态氮的吸收利用策略

Large macroalgal blooms (green tides, Ulva prolifera) occurred in the Yellow Sea, China, yearly from 2007 to 2015. It has been performed lots of investigations on the origin and mechanism of green tides until now. However, some crucial issues are still unsolved. At present, the role of nitrogen (especially organic forms) to the blooms of green tides during the mid-late period is unclear. Additionally, it is difficult to analyze the assimilation of U. prolifera thalii to different species of nitrogen by routine methods, as well as the absorption of macroalgal fronds to one species among the mixed nitrogen substrates. The present project will be designed to conduct with laboratory simulation experiments to study the assimilation efficiency of U. prolifera to inorganic and organic nitrogen during the mid-late macroalgal blooms by using 15N-stable isotope labeling method. Hence, we intend to carry out the following researches: (1) the growth and nutrient uptake responses of U. prolifera during the mid-late period to different nitrogen substrates will be assessed in the laboratory, and we will examine the U. prolifera preferring which species of nitrogen during the mid-late macroalgal blooms; (2) we will examine whether the activity of the important enzyme that affected the nitrogen assimilation are indicators as nitrogen availability during the process of nitrogen assimilation; (3) the influence of temperature, salinity and illumination on the assimilation of different species of nitrogen by U. prolifera will be investigated in the laboratory. Combining the field nitrogen concentrations in the Yellow Sea, we expected to provide indications on factors responsible for the occurrence of macroalgal blooms (especially the mid-late period), and contribute to understanding the mechanism of these blooms of U. prolifera in China.

我国黄海已连续九年暴发浒苔灾害，关于其起因与机制目前已开展大量研究，然而仍有一些关键科学问题尚未完全解析。目前关于不同形态的氮营养盐（尤其是有机氮）在浒苔暴发中后期的作用仍是认知盲点，且常规的营养盐添加试验难以有效解析浒苔对不同氮的藻内利用情况及对混合氮源中某种形态氮的吸收利用。本项目拟通过室内模拟实验，以绿潮暴发中后期的浒苔为研究对象，运用稳定15N同位素技术，开展以下研究：（1）浒苔对不同氮（无机氮和有机氮）的同化效率，探究中后期浒苔对不同氮的优选性；（2）研究浒苔体内关键酶活（硝酸还原酶、谷氨酰胺合成酶、脲酶、氨基酸氧化酶）对不同氮同化效率的表征；（3）浒苔对不同氮的同化效率与关键酶活等受环境因子（温度、盐度、光照）的影响作用。本项目将结合已获得的浒苔暴发区氮浓度的现场数据，明确氮的不同形态（尤其是有机氮）在浒苔暴发中后期的支撑与调控作用，为进一步解析浒苔暴发机制提供新的科学依据。

2007-2019年我国黄海已连续13年爆发浒苔绿潮灾害，关于其起因与机制目前已开展大量研究，然而仍有一些关键科学问题尚未完全解析。目前关于不同形态的氮营养盐（尤其是有机氮）在浒苔爆发中后期的作用仍是认知盲点。为此，本项目以肇事藻种-浒苔为研究对象，采用室内实验和现场数据分析相结合的方法，探究不同形态氮的关键调控作用。通过室内培养实验，我们发现不同形态的氮营养盐（硝酸盐、铵盐、尿素、游离态氨基酸）均可促进浒苔的生长，进一步采用15N同位素标记法，结果发现浒苔不仅可以吸收无机氮，也可以直接吸收利用某些小分子的有机氮。结合黄海浒苔绿潮生消不同阶段的现场调查数据（3-9月），我们发现在浒苔绿潮爆发初期，海水中的溶解无机氮（DIN）快速下降，当到达中后期时，此时DIN浓度处于较低水平，溶解无机氮（DON）浓度开始快速下降。结合室内实验结果，我们推断，不同形态的氮营养盐均可促进浒苔的生长，当无机氮浓度处于较低水平时，有机氮是支撑浒苔绿潮中后期爆发的重要营养元素。此外，我们验证了不同光照和环境因子对浒苔藻体内硝酸还原酶（NRA）活性的影响，发现在最适温度（15℃）和光照（75W.m-2）条件下，浒苔的NRA活性最大。本项目的研究成果证明了海水中的氮营养盐（无机氮和有机氮），在浒苔的生长过程中起到关键的营养支撑作用。尤其是有机氮，对于浒苔绿潮的中后期爆发起到了重要的营养支撑作用。这些研究成果为合理高效的治理浒苔绿潮，保护近海生态环境和国民经济财产起到重要的参考。