环境因素影响藻类生物标志物氢同位素分馏的综合研究

Compound-specific hydrogen isotope ratios of algal biomarkers have been widely applied in the reconstruction of paleoclimate and paleoenvironment. However, hydrogen fractionations in algae are subjected to the effects of environmental factors such as temperature, salinity and nutrient-based growth rates. Previous batch cultures and field study often reported conflict results because it was difficult to isolate a single factor in such practices. ..We plan to perform a comprehensive study to address the effects of environmental factors on hydrogen isotope fractionation in algal biomarkers by combining lab culture and field study. The strategy is to adopt chemostatic culture to address effects of temperature, salinity and nutrient-dependant growth rates, and to use oscillating grids to study the effects of turbulence. We will investigate how the fractionation factors and temperatures are related (linearly or exponentially), and if there is a tolerance range for salinity effect. We expand our previous nitrogen limitation study to phosphate, iron and silicon (for diatom only), and gain insight into how they affect hydrogen isotope fractionation in biomarkers synthesized with different pathways. ..Algal blooms often constitute a majority of the primary productivity in oceans and lakes, though they occur only for a short period. However, a sediment interval for paleoenvironmental reconstruction often has annual to centennial resolution. If fractionation factors change in response to dramatically increased growth rates during the bloom under favorable temperature and nutrient supply, it is important to understand if paleohydrology reconstructed this way could stand for annual mean condition. We plan to collect samples before, during and after algal blooms in the East China Sea and South China Sea as well as Taihu Lake, and simulate it in the lab. Together with compound-specific carbon isotopes, our aim is to lay a firm foundation for application of hydrogen isotope ratios of algal biomarkers in paleoenvironmental reconstruction.

海洋和湖泊藻类的生物标志物氢同位素分馏程度会受到环境因素如温度、盐度、生长速率、营养盐的供应等的影响。分批式培养往往不能孤立出某一个环境因素。本申请书计划引进恒化培养的方式，每次只改变一个参数，探讨该环境因素对生物标志物氢同位素分馏的影响：温度和分馏系数是否存在线性或者指数相关性；探讨盐度变化对氢同位素分馏系数的变化是否存在线性关系或存在一定程度的容忍性；不同营养盐如N、P、Fe等引起的生长速率改变如何影响生物标志物氢同位素分馏。同时结合以单体碳同位素，探讨是否存在合成代谢机制改变。在实验室里模拟紊流，讨论它对藻类生物标志物氢同位素分馏的影响。..海洋里和湖泊里大部分初级生产力往往是在藻类暴发的短时间内完成的。生长速率的迅速变化是否会影响到氢同位素分馏系数？基于此重建的水文条件能否反映年度平均值？结合实验室模拟和捕获器采样来回答这些问题，从而为它们在古环境重建中的应用奠定更为坚实的基础。

本项目通过恒化培养的方式，研究环境因素，包括营养盐浓度、生长温度和盐度对藻类生物标志物氢同位素分馏的影响。同时结合以单体碳同位素，探讨是否存在合成代谢机制改变。我们以通常用的f/2 培养基为基础，设定4个营养盐浓度梯度的，分别相当于f/2 培养基硝酸根浓度的1/25, 1, 50和200倍。目前已经完成颗石藻Emiliania huxleyi在4个营养盐浓度梯度，Gephyrocapsa oceania在3个营养盐浓度梯度的恒化培养实验。温度计划设定15, 18, 22和25°C四个梯度。目前已经完成E. huxleyi和G. oceania在18和22°C温度的培养实验。其它温度以及盐度效应的培养实验尚在进行中。. 初步的结果表明，22°C时，在50倍硝酸根浓度时, E. huxleyi和G. oceania藻细胞的长链烯酮含量最为丰富，但增加到200倍时，E. huxleyi细胞数锐减，烯酮含量降低。从1/25, 1到 50倍NO3-浓度，培养的E. huxleyi和G. oceania长链烯酮的单体δ13C值逐步偏负，和NO3-浓度形成负相关关系。但增加到200倍时， δ13C值开始偏正。G. oceania的长链烯酮δD的变化与δ13C值相反，整体呈现NO3-浓度越高，δD值偏正的趋势。. 温度对照组的培养实验表明，和18℃培养的相比，22℃下培养的E. huxleyi藻细胞数目较少，但烯酮的含量相对较高，而且长链烯酮δ13C值偏正。颗石藻长链烯酮的δD还没得及分析。. 我们完成了两次基金委共享航次，从南海和东海获得了不同盐度的表层海水进行过滤，目前已经完成生物标志物的萃取和硅胶柱分离，正在进行脂肪酸和甾醇的衍生化，为单体同位素分析做准备。. 由于2016年的工作调动，需要从头开始建设实验室，由于各种原因加上中美贸易战等原因，实验室建设和仪器到位远比计划的晚。疫情导致的实验室关闭不得不使得培养试验从头来过。导致执行进度落后于计划。目前盐度的培养实验和其它藻类的培养实验仍然在进行中，争取2021年完成计划。