秦皇岛近海褐潮高发区浮游植物的碱性磷酸酶活性分析

Alkaline phosphatase activity of phytoplankton in Qinhuangdao coastal waters with frequent brown tide occurrences

碱性磷酸酶(Alkaline phosphatase,AP)是浮游植物在磷胁迫状态下表达的一种水解有机磷源的胞外酶,可用于指示海区浮游植物的磷胁迫状态。本研究于2013年7月,对秦皇岛近海抑食金球藻(Aureococcus anophagefferens)褐潮发生期间浮游植物的碱性磷酸酶活性(AP activity,APA)进行研究,结合其他理化参数,分析藻华发生时浮游植物的磷营养状态及其对海水中磷源的水解与利用情况。结果表明,褐潮发生时,抑食金球藻细胞密度高达108个/L,溶解有机磷(Dissolved organic phosphorus,DOP)成为浮游植物生长利用的主要磷源。抑食金球藻的细胞密度受到海水中NO3–、DOP、溶解无机磷(Dissolved inorganic phosphorus,DIP)浓度等的显著影响。浮游植物大量表达AP水解DOP,平均APA高达217.72 nmol/(μg·h)±90.86 nmol/(μg·h)(350.44 nmol/(L·h)±130.57 nmol/(L·h)),且APA随浮游植物生物量增大而显著增加。该结果表明抑食金球藻褐潮发生时,海区遭受严峻的磷胁迫甚至限制。磷源,尤其是有机磷源的可利用性可能在秦皇岛海区抑食金球藻褐潮的发生和维持中起关键作用。

Alkaline phosphatase（AP） is a type of ectoenzyme that is expressed by phytoplankton under phosphorus（P） stress states and can hydrolyze dissolved organic P（DOP）. AP has been widely used to indicate the P stress status of phytoplankton in the sea. In this study, the AP activity（APA） of phytoplankton during the brown tide of Aureococcus anophagefferens that occurred near the coastal waters of Qinghuangdao was investigated in July 2013. The P status of phytoplankton and the capability of phytoplankton in using DOP during the bloom were analyzed. The results show that the density of A. anophagefferens was as high as 10^8 cells/L when the bloom occurred in the coastal area of Qinhuangdao. DOP was the main P source for phytoplankton growth. The densities of A. anophagefferens showed positive correlations with NO3^-, DOP, dissolved inorganic P, and so forth. Phytoplankton expressed abundant AP, and the average APA in water reached as high as 217.72 nmol/（μg·h）chla ± 90.86 nmol/（μg·h）chla（350.44 nmol/（L·h） ± 130.57 nmol/（L·h））. APA increased significantly with phytoplankton biomass. Our results suggest that A. anophagefferens experienced severe P stress or even P limitation when the brown tide occurred. The bioavailability of P, particularly DOP, may play a key role in the occurrence and persistence of the brown tide of A. anophagefferens in the coastal waters of Qinhuangdao.