Abstract Organic nutrients can constitute the major fractions (up to 70%) of aquatic nitrogen (N) and phosphorus (P), but their cycling is poorly understood relative to the inorganic pools. Some phytoplankton species access P from the dissolved organic phosphorus (DOP) pool through expression of alkaline phosphatase (AP), which hydrolyses orthophosphate from organic molecules, and is thought to occur either at low concentrations of dissolved inorganic P (DIP), or elevated ratios of dissolved inorganic N (DIN) to DIP. Three algal strains native to the North-East Atlantic Ocean (coccolithophore, dinoflagellate and diatom species) were grown under representative, temperate conditions, and the dissolved N and P components amended to include dissolved organic N (DON) and DOP. The activity of AP was measured to determine the rate of DOP uptake by each algal species. The addition of DON and DOP enhanced the growth of the algal species, regardless of DIN and DIP concentrations. In cultures where the total concentrations and absolute N: P ratio was unchanged but the N pool included both DON and DIN, an increase in alkaline phosphatase activity (APA) was measured. This suggested that the presence of DON triggered the selective uptake of DOP. The uptake of organic P was confirmed by detection of adenosine in DOP-amended culture media, indicating that P had been cleaved from ADP and ATP added to the media as DOP, and cellular P concentration in these cultures exceeded the calculated concentration based on uptake of DIP only. Our data demonstrates that organic nutrients can enhance and sustain marine algal productivity. The findings have implications for marine ecosystem function and health, since climate change scenarios predict variable riverine inputs to coastal areas, altered N: P ratios, and changes in the inorganic to organic balance of the nutrient pools.

中文翻译：

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溶解有机氮的存在增强了海洋浮游植物对溶解有机磷的吸收

摘要 有机养分可以构成水生氮 (N) 和磷 (P) 的主要部分（高达 70%），但它们的循环相对于无机池知之甚少。一些浮游植物物种通过碱性磷酸酶 (AP) 的表达从溶解的有机磷 (DOP) 池中获取磷，碱性磷酸酶 (AP) 从有机分子中水解正磷酸盐，并且被认为发生在低浓度的溶解无机磷 (DIP) 或高比例下溶解无机氮 (DIN) 到 DIP。三种原产于东北大西洋的藻类菌株（球藻、甲藻和硅藻物种）在具有代表性的温带条件下生长，并且溶解的 N 和 P 成分被修正为包括溶解的有机 N (DON) 和 DOP。测量 AP 的活性以确定每个藻类物种对 DOP 的吸收率。无论 DIN 和 DIP 浓度如何，DON 和 DOP 的添加都促进了藻类的生长。在总浓度和绝对 N:P 比不变但 N 库同时包含 DON 和 DIN 的培养物中，碱性磷酸酶活性 (APA) 的增加被测量到。这表明 DON 的存在触发了 DOP 的选择性摄取。通过在 DOP 修正的培养基中检测腺苷证实了有机 P 的吸收，表明 P 已从 ADP 中裂解，ATP 作为 DOP 添加到培养基中，这些培养物中的细胞 P 浓度超过了基于摄取的计算浓度仅 DIP。我们的数据表明，有机营养素可以增强和维持海藻生产力。