三角褐指藻及其藻际细菌对不同无机氮源的响应

Responses of Phaeodactylum tricornutum and its bacteria in the phycosphere to different inorganic nitrogen sources

海洋生态系统中,浮游植物和细菌之间的相互作用是影响营养盐供应和再生、海洋初级生产力和生物地球化学循环的基本生态关系。为研究营养盐、浮游植物和细菌之间的关系,在实验室内培养条件下,通过改变氮源的形态(硝态氮和铵态氮)和浓度,研究海洋浮游植物三角褐指藻(Phaeodactylum tricornutum)的藻际细菌在不同营养条件下的响应。通过测定不同体系中的无机氮浓度、藻体内氮浓度和三角褐指藻及其藻际细菌的生物量变化,探讨了藻-菌生物量变化的差异以及氮浓度和藻生长的关系;采用二代高通量测序(16S rDNA)的方法分析了三角褐指藻生长过程中的细菌群落结构。结果发现,具有分泌铵态氮促进藻类生长功能的噬甲基菌属(Methylophaga)和海杆菌属(Marinobacter)细菌相对丰度在高浓度(溶液中无机氮浓度为500μmol/L)组中均会随时间的增加而减少。不同培养体系下,促进三角褐指藻生长的氮源主要来自实验初期外部无机氮的添加,并且所有处理组中外部氮消耗率和藻体内氮的增长率近似相等,说明在本实验培养体系中藻际细菌虽然会对不同培养条件有所响应,但对三角褐指藻的生长影响较小。

Interactions between phytoplankton and bacteria represent a fundamental ecological relationship in a marine ecosystem.These interactions influence fundamental processes including nutrient provision,regeneration,primary production,and biogeochemical cycling at the ecosystem level.To further understand the relationship among nutrients,phytoplankton,and bacteria,the effects of bacteria in the phycosphere on the growth of Phaeodactylum tricornutum were studied under different nutritional conditions in a laboratory by changing the type of nitrogen sources(nitrate and ammonium)and concentrations.Changes in the concentration of nitrogen in the solution as well as changes in the nitrogen content,biomass in P.tricornutum,and bacterial abundance in the co-culture system including P.tricornutum and bacteria were measured.The differences in biomass changes of P.tricornutum and bacteria in the phycosphere under different culture systems were studied.The relationship between the nitrogen concentration in the solution and the growth of P.tricornutum was investigated.Bacterial community structure at different growth stages of P.tricornutum was analyzed using the second-generation high-throughput sequencing method(16 S rDNA).The results of sequencing showed that the relative abundance of Methylophaga and Marinobacter,which secrete ammonium to promote the growth of algae,increased with time in the high concentration groups(concentration of inorganic nitrogen:500.0μmol/L).Under different culture systems,the nitrogen source that promotes the growth of P.tricornutum mainly came from the addition of inorganic nitrogen at the beginning of the experiment.The nitrogen consumption rate in the solution and the increased nitrogen content rate in P.tricornutum were approximately equal under different culture systems.These results suggest that although bacteria in the phycosphere respond to different culture conditions,they might have little effect on the growth of P.tricornutum.