PRJDB3316 Excess phosphate loading changes composition and function of bacterioplankton communities in oligotrophic coastal water Phosphorus (P), primarily as phosphate (PO43-), is considered as a key limiting trophic factor in eutrophication of coastal zones. Information on the response of bacterial community to excess PO43- loading in oligotrophic coastal water could provide insights into the micro-ecological effects on the expanding trend of nutrient-enrichment in coastal water. C) and function were studied using 16S Illumina MiSeq sequencing and Biolog-eco plate technologies, respectively, in oligotrophic seawater microcosms manipulated with no perturbation (the control) and a certain level of PO43- in two loading modes: 1) one-off loading at the beginning of incubation; and 2) periodic loadings every two days over a 16-day duration. Our results showed that alpha-diversity of bacterial community was temporally changed but not influenced by P-loading. Bacterioplankton communities across all the treatments showed a similar temporal pattern. P-loading mode significantly affected BCC (Global ANOSIM R = 0.466, P = 0.001). Temporal succession of bacterial community was correlated with pH, Temp, dissolved oxygen, NO2-, NH4+, PO43-, and total phosphorus, and each of these parameters contributed more to community variation than PO43- did. However, excess P-loading increased the temporal turnover rate of bacterial community. Moreover, excess PO43- inhibited metabolic activity of heterotrophic bacterial communities in one-off loading microcosms and also decreased their functional diversity, indicating composition and metabolic activity of bacterial community were significantly correlated. These results provide insights into the patterns of bacterioplankton community phylogenetically and functionally responding to excess PO43- loading in oligotrophic coastal water. Excess phosphate loading changes composition and function of bacterioplankton communities in oligotrophic coastal water bioproject PRJDB3316 PRJDB3316 true Phosphorus (P), primarily as phosphate (PO43-), is considered as a key limiting trophic factor in eutrophication of coastal zones. Information on the response of bacterial community to excess PO43- loading in oligotrophic coastal water could provide insights into the micro-ecological effects on the expanding trend of nutrient-enrichment in coastal water. C) and function were studied using 16S Illumina MiSeq sequencing and Biolog-eco plate technologies, respectively, in oligotrophic seawater microcosms manipulated with no perturbation (the control) and a certain level of PO43- in two loading modes: 1) one-off loading at the beginning of incubation; and 2) periodic loadings every two days over a 16-day duration. Our results showed that alpha-diversity of bacterial community was temporally changed but not influenced by P-loading. Bacterioplankton communities across all the treatments showed a similar temporal pattern. P-loading mode significantly affected BCC (Global ANOSIM R = 0.466, P = 0.001). Temporal succession of bacterial community was correlated with pH, Temp, dissolved oxygen, NO2-, NH4+, PO43-, and total phosphorus, and each of these parameters contributed more to community variation than PO43- did. However, excess P-loading increased the temporal turnover rate of bacterial community. Moreover, excess PO43- inhibited metabolic activity of heterotrophic bacterial communities in one-off loading microcosms and also decreased their functional diversity, indicating composition and metabolic activity of bacterial community were significantly correlated. These results provide insights into the patterns of bacterioplankton community phylogenetically and functionally responding to excess PO43- loading in oligotrophic coastal water.