Responses in growth and succession of the phytoplankton community to different N/P ratios near Dongtou Island in the East China Sea

In the present study, a microcosm experiment was conducted for 12 days during the spring near Dongtou Island in the East China Sea with the aim of investigating the effects of different nitrogen-phosphorus (N/P) ratios (1N:1P, 4N:1P, 16N:1P, 64N:1P, and 256N:1P) on phytoplankton community growth and succession. The results indicated that the cell abundance, chlorophyll a (chl a) concentration, specific growth rate, diversity indices, and species composition of the phytoplankton community varied significantly with the N/P ratios. A higher growth rate (evaluated based on cell abundance and chl a) of the phytoplankton community was observed during the early phase of test (days 1 to 4) with high N/P ratio treatments and with low N/P ratio treatments during the late phase of test (after day 6). The H′ was most the sensitive among the diversity indices we used in the present study, and it decreased significantly in the low N/P ratio treatments on day 4 but increased in the low N/P ratio treatments on day 8 and day 12. On the other hand, a definite community succession order from diatoms (Skeletonema costatum) to dinoflagellates (Protoperidinium bipes and Prorocentrum donghaiense) was observed in all treatments. However, the proportion and occurrence time of the dominant species varied with different N/P treatments.

► We conducted a microcosm experiment immediately before a dinoflagellate bloom.
► Growth was observed to change with N/P ratios during the test.
► The H′ was most the sensitive among the diversity indices we used.
► A community succession order from diatoms to dinoflagellates was observed.
► The proportion and occurrence time of the dominant species varied with N/P ratios.