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 photosynthetically available radiation (PAR)) and two temperatures (20 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 ("E max "). Adding E max 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 E max for WH8102 while both the BWF and E max 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 BWF E max /P-E model estimates that UV + PAR exposure inhibits Synechococcus photosynthesis from 78 to 91 % at 1 m, and integrated productivity to 150 m 17-29 % relative to predicted rates in the absence of inhibition.

Interactive Effect of UVR and Phosphorus on the Coastal Phytoplankton Community of the Western Mediterranean Sea: Unravelling Eco-Physiological Mechanisms

“…abundance and biomass. This result agrees with previous findings showing that eukaryotic phytoplankton have a higher photoacclimation potential than do picoprokaryotic species when both undergo identical experimental light conditions in oligotrophic marine areas [ 80 , 81 ].…”

Photoinactivation of Photosystem II in Prochlorococcus and Synechococcus

“…In contrast Prochlorococcus tends to merely endure transient exposure to excess excitation and might trend towards mixotrophy under some conditions [ 133 ] when maintaining photosynthesis becomes untenable. These contrasting patterns also underlie findings of different excitation tolerance thresholds for the different picocyanobacteria [ 95 , 96 ], and their niche partitioning [ 97 ].…”

“…Photoinactivation and the regeneration of PSII through the PSII repair cycle imposes a significant metabolic burden upon the organism [ 91 – 94 ], which in turn places ecological limits upon their achieved niches and productivity [ 95 , 96 ]. Given the ecological importance of Synechococcus and Prochlorococcus , and their differential strategies to manage and exploit excitation [ 8 , 95 – 97 ] we sought to characterize the photoinactivation of PSII in these species.…”

The interactive effects of stratospheric ozone depletion, UV radiation, and climate change on aquatic ecosystems

“…As a step towards incorporating effects of UV radiation into productivity models, empirical formulas have been developed recently to represent the inhibitory effects of UV radiation on photo-synthesis in key species of phytoplankton in the open ocean. 149,150 Critical to these calculations are biological weighting functions, which provide descriptions of the effectiveness of specific wavelengths of UV radiation for biological processes such as the inhibition of photosynthesis ( Fig. 4).…”