珠江口最大浑浊带中高浮游细菌丰度的机制研究

Turbidity maximum zone (TMZ) is the dynamic region in an estuary, characterized by higher concentration of suspended matters than upstream and downstream of the estuary. The abundance of heterotrophic bacterioplankton in the TMZ is higher than its adjacent water, and they likely are the major prey of zooplankton. However, little is known about the reason why bacterioplankton abundance is extremely high in the TMZ. Previous studies showed that bacterial metabolic activity was strongly associated with the quantity and bioavailability of organic carbon. My project will determine the origin and concentration of organic carbon, enzymatic hydrolysis process of organic carbon, and (bacterial production, respiration and growth efficiency) in the water column in the TMZ and non-TMZ of the Pearl River Estuary. The linkage of the concentration and bioavailability of organic carbon and bacterial metabolism will be discussed to address why bacterioplankton abundance in the TMZ is higher than its adjacent waters.

最大浑浊带是河口中含沙浓度稳定地高于其上下游，且在一定范围内有规律迁移的浑浊水体，是一种广泛存在于全球潮汐河口中的重要自然现象。调查发现最大浑浊带中异养浮游细菌丰度远高于周围水域，可能是浑浊带浮游动物的主要食物来源。然而，我们对浑浊带高细菌丰度现象的形成机制尚不清楚。已有研究表明，细菌代谢活动与溶解有机碳的总量及生物可利用性密切关联；由此推测，最大浑浊带中高细菌丰度的主要原因可能与此相关。本项目拟以珠江口最大浑浊带为主要研究区域，比较分析最大浑浊带与非浑浊带水体中有机碳水平与来源、有机碳的酶水解过程，以及细菌代谢活动（细菌生产力、呼吸速率和生长效率），明确浑浊带有机碳的来源以及不同形态有机碳转化的过程，探讨细菌代谢活动与有机碳生物可利用性的内在联系，揭示浑浊带高细菌丰度的机制。

本研究以珠江口为研究区域，研究了珠江口细菌代谢和细菌丰度的主控因素，从而揭示了浑浊带高细菌丰度的机制。取得以下重要成果（1）悬浮颗粒物是珠江口细菌丰度的重要控制因素，它为细菌的生长提供了载体和营养，提高了附生细菌在异养细菌群落中的比例。（2）珠江口的细菌代谢具有明显的季节变化，与有机碳的季节变化相互关联。在溶解有机碳（DOC）含量充足的春季，细菌生产力（BP）主要受DOC活性调控，进而调控了附生细菌的分布。而在DOC含量相对不足的夏季和冬季，细菌的胞外酶活性发挥了重要作用，使大分子有机碳转化为可供细菌直接吸收利用的小分子DOC，并调控了细菌生产力的分布。