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Background: Clarifying the relationship between photosynthesis and irradiance and accurately quantifying photosynthetic performance are of importance to calculate the productivity of phytoplankton, whether in aquatic ecosystems modelling or obtaining more economical production. Results:The photosynthetic performance of seven phytoplankton species was characterized by four typical photosynthesis-irradiance (P-I) response models. However, the differences were found between the returned values to photosynthetic characteristics by different P-I models. The saturation irradiance (I sat ) was distinctly underestimated by model 1, and the maximum net photosynthetic rate (P nmax ) was quite distinct from its measured values, due to the asymptotic function of the model. Models 2 and 3 lost some foundation to photosynthetic mechanisms, that the returned I sat showed significant differences with the measured data. Model 4 for higher plants could reproduce the irradiance response trends of photosynthesis well for all phytoplankton species and obtained close values to the measured data, but the fitting curves exhibited some slight deviations under the low intensity of irradiance. Different phytoplankton species showed differences in photosynthetic productivity and characteristics. Platymonas subcordiformis showed larger intrinsic quantum yield (α) and lower I sat and light compensation point (I c ) than Dunaliella salina or Isochrysis galbana. Microcystis sp., especially M. aeruginosa with the largest P nmax and α among freshwater phytoplankton strains, exhibited more efficient light use efficiency than two species of green algae. Conclusions:The present work will be useful both to describe the behavior of different phytoplankton in a quantitative way as well as to evaluate the flexibility and reusability of P-I models. Meanwhile we believe this research could provide important insight into the structure changes of phytoplankton communities in the aquatic ecosystems. Publisher's NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Vertical migration patterns of different phytoplankton species were examined during a summer bloom period in Dianchi Lake, China. The ratio of the mean crowding to mean density (x*/x) and mean residence depth (MRD) was used to quantitatively evaluate the distribution patterns. The effects of wind velocity and water column temperature differences on the vertical distribution patterns of Microcystis aeruginosa, Aphanizomenonflos-aquae, and total phytoplankton were then investigated. Over 5 days (July 16-20, 2013), abundant of Microcystis aeruginosa (1.10 ± 0.40 9 10 9 cells/L), Aphanizomenonflos-aquae (5.11 ± 1.38 9 10 7 cells/L), and total phytoplankton (1.24 ± 0.40 9 10 9 cells/L, 239.63 ± 79.26 lg/LChl-a, n = 64) were found throughout the water column. Values of x*/x and MRD showed that Microcystis aeruginosa aggregated on the water surface during the calm morning [wind velocity (WV) \2 m/s], and distributed uniformly in the windy afternoon (WV [2-3 m/s). Aphanizomenonflosaquae tended to be randomly distributed for most of the time. Wind velocity was significantly correlated with the x*/x and MRD of Microcystis aeruginosa (P \ 0.05), but not with those of Aphanizomenonflos-aquae. Meanwhile, the effects of thermal differentiation on the vertical distributions of all species were not significant. Therefore, the vertical distributions of Microcystis aeruginosa may be determined by wind velocity rather than thermal differentiation in Dianchi Lake.