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Photosynthetic response of Nodularia spumigena to UV and photosynthetically active radiation depends on nutrient (N and P) availability

Roleda, Michael Y., Mohlin, Malin, Pattanaik, Bagmi, Wulff, Angela
FEMS microbiology ecology 2008 v.66 no.2 pp. 230-242
Nodularia spumigena, biomass, euphotic zone, light intensity, nitrates, nitrogen, nitrogen-fixing cyanobacteria, orthophosphates, phosphorus, photoinhibition, photons, photosynthetically active radiation, photosystem II, summer, Baltic Sea
Biomass of N. spumigena is distributed within the dynamic photic zone that changes in both light quantity and quality. This study was designed to determine whether nutrient status can mitigate the negative impacts of experimental radiation treatments on the photosynthetic performance of N. spumigena. Cyanobacterial suspensions were exposed to radiation consisting of photosynthetically active radiation (PAR=400-700 nm), PAR+UV-A (=PA, 320-700 nm), and PAR+UV-A+UV-B (=PAB, 280-700 nm) under different nutrient media either replete with external dissolved nitrate (N) and orthophosphate (P; designated as +N/+P), replete with P only (-N/+P), or replete with N only (+N/-P). Under low PAR (75 μmol photons m⁻² s⁻¹), nutrient status had no significant effect on the photosynthetic performance of N. spumigena in terms of rETRmax, α, and Ek. Nodularia spumigena was able to acclimate to high PAR (300 μmol photons m⁻² s⁻¹), with a corresponding increase in rETRmax and Ek. The photosynthetic performance of N. spumigena cultured with supplemental nitrogen was more susceptible to experimental PAR irradiance. Under UVR, P-enrichment in the absence of additional external N (-N/+P) induced lower photoinhibition of photosynthesis compared with +N/-P cultures. However, the induction of NPQ may have provided PSII protection under P-deplete and PAR+UVR conditions. Because N. spumigena are able to fix nitrogen, access to available P can render them less susceptible to photoinhibition, effectively promoting blooms. Under a P-deficient condition, N. spumigena were more susceptible to radiation but were capable of photosynthetic recovery immediately after removal of radiation stress. In the presence of an internal P pool in the Baltic Sea, which may be seasonally available to the diazotrophic cyanobacteria, summer blooms of the resilient N. spumigena will persist.