珠江口异养细菌时空分布特征及其调控机制

河口是海陆相互作用的重要地带, 往往呈现出独特的生物地球化学过程, 是研究碳循环过程的重要场所。在春季(2015年5月)、夏季(2015年8月)和冬季(2016年1月)分别对珠江口海域异养附生细菌和游离细菌时空分布及其各自高核酸(HNA)、低核酸(LNA)类群的相对贡献进行了调查研究, 并对其调控因子进行了相应探讨。结果表明, 珠江口异养细菌分布具有明显的时空差异。空间分布上, 珠江口异养细菌丰度自河口上游至下游呈递减趋势, 主要与上游污水输入以及珠江径流与高盐外海水在河口内的混合有关; 在雨季, 河口中下游盐度锋面区出现异养细菌丰度和叶绿素a质量浓度的高值区, 锋面区使营养物质停留时间增加, 促进浮游生物生长。垂直方向上, 表层异养细菌丰度略高于底层。时间尺度上, 异养细菌总丰度在春季最高(表层均值为2.94±1.23×10⁹个 ?L^-1, 底层为2.81±1.50×10⁹个 ?L^-1), 夏季次之(表层均值为2.32±0.43×10⁹个 ?L^-1, 底层为1.90±0.50×10⁹个 ?L^-1), 冬季最低(表层均值为1.06±0.33×10⁹个 ?L^-1, 底层为9.76± 3.44×10⁸个 ?L^-1)。珠江口海域异养细菌以附生细菌为主, 占异养细菌总丰度的16.56%~96.19%, 整体分布较稳定, 冬季最高(平均78.65%)、夏季(70.32%)与春季相近(68.17%)。附生细菌以代谢活跃的HNA类群为主, 游离细菌则主要以LNA类群为主, 代谢活性整体相对较低。

Spatial and temporal variation in heterotrophic bacteria and their regulators in the Pearl River Estuary

Estuaries are important land-sea interaction zones with unique biogeochemical processes and are important places to study the carbon cycle. Little is known on bacterial regulation in carbon cycling in the Pearl River Estuary. To examine the relative contribution of different groups of heterotrophic bacteria (particle-attached bacteria vs free-living bacteria, and high nucleic acid bacteria vs low nucleic acid bacteria), spatial and temporal variation in heterotrophic bacterial abundance was investigated during three contrasting periods (May 2015, August 2015 and January 2016) in the Pearl River Estuary. The total bacterial abundance was the highest in spring (an average of 2.94±1.30×10⁹ cells ?L^-1 at the surface and 2.81±1.50×10⁹ cells ?L^-1 at the bottom), moderate in summer (2.32±0.43×10⁹ cells ?L^-1 at the surface and 1.85±0.50×10⁹ cells ?L^-1 at the bottom), and the lowest in winter (1.06±0.33×10⁹ cells ?L^-1 at the surface and 9.76±3.44×10⁸ cells ?L^-1 at the bottom). Bacterial abundance at the surface was slightly higher than that at the bottom. Bacterial abundance decreased spatially from the upstream to the downstream of the estuary, suggesting that sewage input contributed to high bacterial abundance in the upstream, and that the downstream decrease resulted from the mixing of river discharge and seawater. The peaks of bacterial abundance and Chl a were observed at the frontal zone in the wet season, since a front increased the residence time of nutrients and plankton, and favored plankton growth. According to the spatial variation trend of bacterial abundance, it could be inferred that the heterotrophic bacteria of the estuary mainly came from upstream inputs. Heterotrophic bacterial communities were dominated by particle-attached bacteria, which accounted for 78.65%, 70.32% and 68.17% of the total bacterial abundance in spring, summer and winter, respectively. The metabolically active bacteria with high nucleic acid dominated in the particle-attached bacteria, while the low nucleic acid group was the dominant component of the free-living bacteria.