College of Oceanography, Hohai University, Nanjing, 210024, PR China; Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, 361005, PR China; College of Marine Living Resource Sciences and Management, Shanghai Ocean University, Shanghai, 201306, PR China; Observation and Research Station of Island and Coastal Ecosystem in the Western Taiwan Straits, Ministry of Natural Resources, Xiamen, 361005, PR China.
Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, 361005, PR China; College of Marine Living Resource Sciences and Management, Shanghai Ocean University, Shanghai, 201306, PR China.
Environ Res. 2024 Jul 1;252(Pt 4):119090. doi: 10.1016/j.envres.2024.119090. Epub 2024 May 7.
The distribution and mechanisms of photosynthetically dissolved organic carbon (PDOC) released by marine phytoplankton are frequently neglected and inadequately understood because most studies on carbon sequestration capacity have focused on photosynthetic particulate organic carbon. In this study, percentage extracellular release (PER) and its environmental influencing factors were investigated for 10 cruises in the Taiwan Strait during 2006-2023. The results indicated that the PER increased horizontally from the nearshore to the off-shelf and vertically from the surface to the bottom within the euphotic zone. PER tends to be low in eutrophic waters such as upwellings and estuaries and high in oligotrophic waters. The study revealed that the average contribution of PDOC to total primary productivity (TPP) in the Taiwan Strait could reach 18.2 ± 11.7%, which is similar to the previously estimated global oceanic values. PDOC production satisfied approximately 25% the carbon requirements of heterotropic bacteria (HB). A detailed analysis of the PER combined with model simulations proved that the distribution of the PER in the Taiwan Strait was caused by the joint contribution of irradiance, size-fractionated phytoplankton, and nutrient stoichiometry. Our results contradict the view that the PER is a constant factor that is unaffected by TPP. However, there was a significant negative correlation between the PER and TPP. The PDOC was always lower than the bacterial carbon demand for a broad range of bacterial growth efficiencies, suggesting a weak coupling between phytoplankton exudation and bacterial metabolism. This challenges the idea that there is a well-coupled relationship between bacteria and phytoplankton present on the continental shelf. These findings indicate significant discrepancies in PDOC mechanisms and the quantitative importance of nearshore eutrophic and off-shelf oligotrophic environments. Consequently, it is unwise to use uniform PERs without differentiation under trophic conditions when reevaluating and appraising marine carbon fixation.
海洋浮游植物释放的光合溶解有机碳（PDOC）的分布和机制经常被忽视和理解不足，因为大多数碳封存能力的研究都集中在光合颗粒有机碳上。本研究调查了 2006-2023 年期间台湾海峡 10 次航次的细胞外释放百分比（PER）及其环境影响因素。结果表明，PER 在水平方向上从近岸向离岸增加，在垂直方向上从表层到底层增加，在透光层内。PER 在富营养水域（如上升流和河口）中较低，在贫营养水域中较高。研究表明，PDOC 对台湾海峡总初级生产力（TPP）的平均贡献可达 18.2±11.7%，与之前估计的全球海洋值相似。PDOC 产量满足异养细菌（HB）碳需求的大约 25%。对 PER 的详细分析与模型模拟相结合，证明了 PER 在台湾海峡的分布是由辐照度、粒径分馏浮游植物和营养化学计量的联合贡献造成的。我们的结果与 PER 是不受 TPP 影响的常数因子的观点相矛盾。然而，PER 与 TPP 之间存在显著的负相关。PDOC 始终低于细菌生长效率范围内的细菌碳需求，这表明浮游植物分泌与细菌代谢之间的耦合较弱。这挑战了细菌和浮游植物之间存在良好耦合关系的观点。这些发现表明，在近岸富营养和离岸贫营养环境中，PDOC 机制和近海富营养和离岸贫营养环境中 PDOC 的定量重要性存在显著差异。因此，在重新评估和评价海洋碳固定时，在营养条件下不区分地使用统一的 PER 是不明智的。
