光合作用参数是浮游植物的重要生理学指标，一般通过P-E实验（C14示踪）测量得到。最大光利用（固碳）效率Φm和光饱和固碳速率Pm的函数，表征了浮游植物的光合作用能力，理论上受营养状态、温度等因素的影响。分析光合作用参数的特征和分布规律，有助于更好地了解海洋中的初级生产过程。同时光合作用参数也是构建海洋生态系统数值模型的重要基础。
在CHOICE-C航次的支持下，黄邦钦研究组（Coastal Ecology Group，http://mel.xmu.edu.cn/group/ceg/index.asp）在南海北部获得了4个航次共149个P-E曲线的数据，时间跨度上含春、夏、秋三个季节，空间跨度（近岸、陆架到海盆）上具有明显的营养盐和生物量梯度。通过分析发现，与前人结果相似的是， Φm沿着富营养到寡营养的梯度出现明显的下降，浮游植物群落结构同时发生了粒级的显著改变，从micro-phytoplankton为主变化为以pico-phytoplankton为主。Pm是影响最终初级生产力大小的最重要的参数，虽然在洋盆和全球尺度上的研究表明，温度是估算PBm（单位叶绿素a的光饱和固碳速率）的最好的参数之一，但在许多区域性的系统中，温度通常不是一个很好的指标；我们的研究也发现，在南海北部，PBm的变化与温度的变化，在统计学上无相关关系，但与浮游植物群落结构的变动相关。光合作用、初级生产力与浮游植物群落结构的关系，是近年来和将是今后一段时间内的一个研究热点，与他人的研究结果不同的是，我们的研究发现，PBm的大小，不能在粒级结构上进行很好地区分，以pico-phytoplankton为主的群落的PBm值具有非常大的变化范围，但会随着原绿球藻比例的增加而变小。
该研究展示了从生物量（叶绿素a）到初级生产力转换的关键参数，为水色遥感和生地化研究提供了重要的参考。该成果将刊登于Journal of Geophysical Research: Oceans第120卷第5期。
Reference: Xie, Y., B. Huang, L. Lin, E. A. Laws, L. Wang, S. Shang, T. Zhang, and M. Dai (2015), Photosynthetic parameters in the northern South China Sea in relation to phytoplankton community structure, J. Geophys. Res. Oceans, 120, doi:10.1002/2014JC010415.
Abstract:
Many recent models for retrieval of primary production in the sea from ocean-colour data are temperature-based. But previous studies in low latitudes have shown that models that include phytoplankton community structure can have improved predictive capability. In this study, we measured photosynthetic parameters from photosynthesis-irrandiance (P-E) experiments, phytoplankton absorption coefficients, and phytoplankton community structure derived from algal pigments during four cruises in the northern South China Sea. The maximum quantum yield of CO2 (ΦCm) and the chlorophyll a-normalized P-E curve light-limited slope (αB) varied significantly with the blue-to-red ratio of phytoplankton absorption peaks (aph(435)/aph(676)) (p < 0.001, r = -0.459 and -0.332, respectively). The unexplained variability could be due in part to the absorption associated with non-photosynthetic pigments. The chlorophyll a-normalized light-saturated photosynthesis rate (PBm) at the surface showed a unimodal distribution over the chlorophyll a range during the spring and summer, and significantly increased when Prochlorococcus was outcompeted by other pico-phytoplankton (p < 0.01). Almost 60% of the variance of PBm could be explained by a piecewise regression with phytoplankton absorption coefficients and pigment markers. Unlike previous studies, our data showed that changes of PBm were unrelated to the size structure of phytoplankton. Although a temperature-based approach could not effectively predict αB and PBm in the NSCS, a trophic-based approach can be used for assignment of these parameters in a regional primary production model using ocean-colour data.
Full text available at: http://dx.doi.org/10.1002/2014JC010415
