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Dependency of UVR-induced photoinhibition on atomic ratio of N to P in the dinoflagellate Karenia mikimotoi
- Guan, Wanchun, Li, Ping
- Marine biology 2017 v.164 no.2 pp. 31
- Karenia, absorbance, carotenoids, chlorophyll, correlation, nitrogen, photoinhibition, photophosphorylation, photosynthetically active radiation, photosystem II, phytoplankton, seawater, superoxide dismutase, ultraviolet radiation
- To investigate the effects of Nitrogen (N):phosphorus (P) ratio and solar ultraviolet radiation (UVR) on the growth and photophosphorylation of oceanic phytoplankton, the effects of UVR and N:P ratio on K. mikimotoi were evaluated. K. mikimotoi cells were cultured in artificial seawater (ASW) under five different N:P ratios (1:1, 16:1, 50:1, 100:1 and 200:1) for 15 days (phase 1: 1–5 day; phase 2: 6–10 day; phase 3: 11–15 days). Next, K. mikimotoi cultures were exposed to photosynthetically active radiation (PAR), PAB (PAR + UV-A + UV-B) and PA (PAR + UV-A), respectively. Finally, K. mikimotoi cells grown under the Redfield ratio (16:1) had the largest growth rate (0.257day⁻¹), highest pigment concentrations (chlorophyll a (Chla): 0.465 × 10⁻ ⁵ μg cell⁻¹, carotenoid (Caro): 0.249 × 10⁻⁵ μg cell⁻¹) and maximum superoxide dismutase (SOD) activity (0.9 U × 10⁻⁶ cell⁻¹) compared with those grown under other N:P ratios. The UV-absorbing compounds’ (UVₐbc) absorbance was largest at the N:P ratio of 50:1 during the range of 310–360 nm, with a relatively higher value at the N:P ratio of 16:1. UV intensity was positively correlated with photoinhibition. K. mikimotoi cells grown at the N:P ratio of 16:1 showed the smallest photoinhibition compared to those grown at other N:P ratios under the PAR treatment with the largest r:k ratio; similar results were found for both the PA and PAB treatments. The Redfield ratio of 16:1 is optimal for the growth and photophosphorylation of K. mikimotoi. The weakest UVR-induced photoinhibition at this ratio may be attributed to the highest photosystem II (PSII) repair rate and SOD activity.