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As the major source of atmospheric deposition in the Northwestern Pacific Ocean, Asian dust modulated the community structure and nutrient utilization of phytoplankton. In order to study the effects of Asian dust input on the eukaryotic phytoplankton community structure, onboard encolsure experiments (7days) were performed at 2 stations (K3, 26°11'15.48"N, 136°43'38.46"E; B1, 37°56'12.90"N, 146°59'55.26"E) in the open areas of Northwestern Pacific Ocean in spring 2015. Different amount of Asian dust, 0.2 mgžL-1 (Dust-1) and 2 mgžL-1 (Dust-2) were added into the cultivating system. Daily changes in chlorophyll-a, nutrients and eukaryotic phytoplankton abundance were monitored. Water from the 0th, 2nd, 4th and 7th day cultivation were collected for metabarcoding sequencing.

The results showed that concentration of NO3--N increased significantly while concentration of NO2--N, PO43--P and SiO32--Si did not changed due to the dust input. During the cultivation, concentration of NO3--N and SiO32--Si decreased dramatically in dust-2. Simultaneously, no significant difference was found in concentration variation of NO2--N and PO43--P among control and dust groups. Concentration of chlorophyll-a of nano- and micro- eukaryotic phytoplankton increased significantly in dust-2 at 2 stations. However, there was no significant difference of the chlorophyll-a concentration of pico- eukaryotic phytoplankton among control and dust groups. By the end of the cultivation, the eukaryotic phytoplankton abundance in dust-2 was 3.0 and 7.5 folds higher than that in control at K3 and B1. The species number in dust groups decreased at K3 because the diatom bloom interfered the growth of other groups. However, the species number in dust groups increased at B1 because when the dust was added, the N-limited condition was remitted and the hypnospore of diatoms germinated. Diatom growth was promoted in dust-2 at 2 stations and the promoting extent was much more dramatic at B1. Growth of dinoflagellates was interfered at K3 and not changed significantly at B1 in dust groups. Moreover, growth of larger sized groups such as Pseudo-nitzschia, Chaetoceros and Thalassionema were promoted significantly, while growth of smaller sized groups such as Thalassiosira, Prorocentrum, Heterocapsa, and Scrippsiella were interfered or not changed in dust groups at 2 stations.

The results indicated that Asian dust addition could increase the marine productivity and alter the eukaryotic phytoplankton community structure. This research provides important reference for further investigating the effects of dust input on phytoplankton community structure.