UV effects on the primary productivity of picophytoplankton: biological weighting functions and exposure response curves of <i>Synechococcus</i>

Abstract

Abstract. A model that predicts UV effects on marine primary productivity using a biological weighting function (BWF) coupled to the photosynthesis-irradiance response (BWF/P-E model) has been implemented for two strains of the picoplanktonic cyanobacteria, Synechococcus, WH7803 and WH8102, which were grown at two irradiances (77 and 174 μmol m−2 s−1 PAR) and two temperatures (20 °C and 26 °C). The model was fit using photosynthesis measured in a polychromatic incubator with 12 long-pass filter configurations with 50% wavelength cutoffs ranging from 291 to 408 nm, giving an effective wavelength range of 280–400 nm. Examination of photosynthetic response vs weighted exposure revealed that repair rate progressively increases at low exposure but reaches a maximum rate above a threshold exposure ("Emax"). Adding Emax as a parameter to the BWF/P-E model provided a significantly better fit to Synechococcus data than the existing "E" or "T" models. Sensitivity to UV inhibition varied with growth conditions for both strains, but this was mediated mainly by variations in Emax for WH8102 while both the BWF and Emax changed for WH7803. Higher growth temperature was associated with a considerable reduction in sensitivity, consistent with an important role of repair in regulating sensitivity to UV. Based on nominal water column conditions (noon, solstice, 23° latitude, "blue" water), the BWFEmax/P-E model estimates that UV + PAR exposure inhibits Synechococcus photosynthesis from 77–91% at 1 m, and integrated productivity to 150 m 15–27% relative to predicted rates in the absence of inhibition.

Photosystem II repair in marine diatoms with contrasting photophysiologies

“…Alternately, cells below the threshold can induce more rapid PSII repair with a higher k PsbA , or possibly induce protective screening or dissipatory mechanisms (NPQ and/or PSII CET for instance) to increase their tolerance threshold by slowing the rate of PSII photoinactivation under a given light level. These threshold lines are related to E MAX estimates (Neale et al 2014) of the maximum tolerable irradiance before the onset of net photoinhibition. Our measurement of k PsbA was made upon cells treated under 450 lmol photons m -2 s -1 , but grown under 50 lmol photons m -2 s -1 .…”

Effect of CO2, nutrients and light on coastal plankton. IV. Physiological responses

“…PAR is shown as the mean (± SD) irradiance and the minimum and maximum values observed, as well as total doses during the incubation. In addition, we show un-weighted irradiance and predicted ratios of photosynthetic rates under UVR irradiances divided by maximum photosynthetic rates (P/P max , dimensionless) using the biological weighting functions for the inhibition of photosynthesis of Synechococcus grown under medium and high light (Neale et al 2014b), and for the diatom Thalassiosira pseudonana (Sobrino et al 2008) (final conc.) at 20°C for 90 min.…”

“…See Table 1 for PAR and UVR irradiances reaching the samples after correction by the Ultraphan 295 and 395 films, FEP bottle and screen factor (%T = 69%). Un-weighted and weighted UV irradiances using the biological weighting functions for the inhibition of photosynthesis from cultures of Synechococcus under low light and high light, and for the diatom Thalassiosira pseudonana are also included (Sobrino et al 2008, Neale et al 2014b.…”

Differential photosynthetic responses of marine planktonic and benthic diatoms to ultraviolet radiation under various temperature regimes

“…Therefore, the relatively higher absorption in the blue range for benthic species might indicate that temperature enhances the synthesis of xanthophyll-related pigments (Havaux and Tardy, 1996). The differences in absorption spectra of extracted pigments suggest that to better understand the spectral-dependent responses to UV radiation, biological weighting functions should be introduced in this kind of work (Neale et al, 2014).…”