珠江口近海原位多不饱和醛类藻毒素对细菌降解颗粒有机碳的调控机制

The export flux of particulate organic carbon (POC) determines the efficiency of biological pump and thus play an important role in ocean biogeochemical cycle. During its transportation in the water columns, POC can be modified by heterotrophic bacteria via remineralization, which will eventually affect the carbon sequestration into the ocean. Recently, polyunsaturated aldehydes (PUAs), a group of phycotoxin produced by marine diatoms, were found to influence the remineralization and export of POC in the open ocean. The role of PUAs may be more significant in the coastal waters (such as estuarine and shelf waters), where there are often much higher POC fluxes and higher abundances of PUA-producing diatoms compared to the open seas. Our previous studies have revealed a spatial connection between PUAs and POC in the Pearl River Estuary (PRE) and the adjacent shelf-sea, whereas the underlying mechanism of PUAs on regulating POC concentrations and export fluxes remains largely unexplored. In this project, we hope to address the link between POC and PUAs by investigating the effects of PUAs on the abundance and activities of particle associate bacteria that controls the POC remineralization. Besides the in situ PUAs and POC measurements, we will conduct incubation experiments of the particle-associate bacteria with exogenous PUAs additions. By doing these investigations, we seek to understand the role of PUAs in controlling the biological carbon pump, which may be fundamentally essential for our understanding of the global carbon cycle.

海洋颗粒有机碳（POC）的输出通量决定了生物泵的运作效率进而影响海洋碳循环。海洋异养细菌的降解作用影响POC向海洋内部的传输，对全球碳封存起关键作用。多不饱和醛（PUAs）是海洋硅藻应对环境压力产生的一类藻毒素，开放大洋环境下PUAs原位热点浓度能影响颗粒附着细菌降解POC从而调控POC输出。相对大洋环境，河口近海受陆源输入的影响，POC输出通量很高，产PUAs硅藻占优势。已有研究主要是调查PUAs在珠江口近海水体中的分布及其影响因素，尚未阐明其环境下原位PUAs对POC输出的调控机制。因此，本项目将以珠江口近海颗粒附着细菌和POC为研究对象，运用多学科交叉方法，开展PUAs原位热点浓度估算和外源PUAs添加培养实验等研究内容，阐明河口近海环境下原位PUAs对颗粒附着细菌降解POC的调控机制，从本质上揭示PUAs在调控河口近海生物泵运作效率和海洋碳循环中的作用，具有非常重要的科学意义。

海洋硅藻等浮游植物在环境压力下释放多不饱和醛（PUA）作为化学信号物质，其通过介导海洋浮游生物相互作用进而影响生物泵和海洋碳循环。寡营养大洋颗粒有机碳（POC）中的原位PUA可以影响细菌降解颗粒物，而对于富营养近海环境下PUA调控POC的输出机制尚不明确。本项目以珠江口近海作为主要研究区域，围绕海洋生源化学信号物质PUA、合成PUA的浮游植物群落、以及PUA调控的颗粒附着细菌等作为研究对象，以水文动力学、生物地球化学、微生物海洋学等方法为主要技术手段，通过调查和分析珠江口近海合成PUA浮游植物的格局、生源PUA定量分布、以及颗粒物原位PUA浓度量级及其对附着细菌的作用规律，探讨了原位PUA对河口近海环境中POC降解和输出的调控机制：（1）阐明了在珠江口近海跨羽流锋面变化的PUA合成硅藻优势种群，从骨条藻演变为海链藻；（2）揭示了珠江口近海颗粒态PUA在不同层位的来源，表层主要来源于浮游植物，而底层主要来源于沉积物碎屑再悬浮；（3）建立和完善了直接测定颗粒附着细菌丰度的方法（去吸附法），明确了珠江口近海高浑浊水体中颗粒物原位PUA热点浓度为微摩尔量级；（4）揭示了近海环境下PUA影响附着细菌的规律，即低浓度PUA激发细菌生长，群落结构无显著变化，高浓度PUA激发细菌呼吸和生产代谢，群落结构显著变化；（5）阐明了近海PUA通过激发颗粒附着细菌的生长或代谢，增加对POC的矿化降解，减少珠江口近海POC的输出。本项目的开展可为后续深入研究海洋生源化学信号物质在碳循环中的应用提供技术支撑和理论依据。基于本项目的实施，共发表学术论文7篇（包含中科院SCI分区表2区以上6篇，中文核心期刊1篇）。