INFLUENCE OF ULTRAVIOLET RADIATION ON GROWTH AND PHOTOSYNTHESIS OF TWO COLD OCEAN DIATOMS 1

The effects of spectral exposure correspondmg to normal and depleted stratospheric ozone concentrations on photosynthesis and mycosporine-Like amino a c~d s ( W A S ) contents of different natural phytoplankton communities were studied in early austral summer 1995/1996 during the JGOFS ANT XIIY2 cruise in the Atlantic Sector of the Southern Ocean. The radiation conditions were simulated in a special solar simulator in which the same sample was incubated under 2 light regimes differing in UV-B doses In all phytoplankton samples the quantum yield of electron transport in photosystem I1 (PSII) decreased after incubation under increased ultraviolet radiation (UVR) levels. Only samples outside of phytoplankton blooms showed a significant lowering of photosynthetic production rate due to enhanced UV-B. Phytoplankton cells within the blooms probably received protection from UV-absorbing MAAs, because only there cells, chains or colonies of phytoplankton communities were large enough to act in combination with MAAs as effective sunscreens. In addition, witkm the blooms, due to shallow upper mixed layers (UMLS) and stability within the water column, cells had probably enough light to maintain turnover rates of repair mechanisms at PSII and induce sufficient MAA synthesis; these processes were able to compensate for the negative effects of UVR. In contrast, the darnaging effect on photosynthesis was much more severe on phytoplankton cells outside the blooms; most cells (70 to 90%) here were too small to receive protection from the MAAs present, and UMLs were deep and mixing rates high.

Section: Impact Of Increased Uvrsupporting

confidence: 76%

Simulation of the effects of naturally enhanced UV radiation on photosynthesis of Antarctic phytoplankton

Bracher¹,

Wiencke²

2000

“…Lamp design indicating the experimental irradiances applied in each treatment (PAR/UVA/UVB ratios = 0.8/1.0/0.1) and the corresponding weighted irradiances calculated using the biologically-effective weighting function for the DNA damage of E. col1 (Setlow 1974) and general plant damage (Caldwell 197 l ) possible masking of UV effects by excessive PAR (Molina & Montecino 1996, Nilawati et al 1997. Moreover, the low level of PAR used was not regarded to be a limiting factor for physiological requirements as studied macroalgae from both Arctic and southern Spain sites are shade-adapted species (Flores-Moya et al 1993, Bischof et al 199813, Hanelt 1998see 'Discussion' (Dring et al 1996a, Nilawati et al 1997, Perez-Rodriguez et al 1998 by the formation of germ tubes and later of embryospores. Since even under white light some fraction of zoospores did not survive (due to imperfect maturity), an average number under PAR alone (GG 400 filter) was used as a control value to set the 100% living germlings.…”

Section: Methodsmentioning

confidence: 99%

Impact of UV-radiation on viability, photosynthetic characteristics and DNA of brown algal zoospores:implications for depth zonation

Wiencke¹,

Gómez²,

Pakker³

et al. 2000

172

114

Measurements of photosynthesis, germination capacity and assessment of DNA damage were carried out in the laboratory to determine the effect of different conditions of ultraviolet (W) and photosynthetically active radiation (PAR) on zoospores of various large brown algae collected on Spitsbergen (Svalbard, High Arctic) and Tarifa (Cbdiz, southern Spain). Results were correlated to in situ light conditions and indicated that zoospores suffer photoinhibition of photosynthesis, loss of viability and DNA damage in relation to the growth depth of parental sporophytes. At both sites, germination capacity of zoospores in species collected in deep waters was more strongly mpaired after exposure to the same UV doses than in species from shallower waters. In general, zoospores exposed to PAR+UVA+UVB showed higher mortality rates than after exposure to PAR+UVA or PAR alone. For Larmnana digitata from Spitsbergen, it was found that the loss of zoospore viability is the result of DNA damage and photodamage of the photosynthetic apparatus. UVB irradiances occurring in southern Spain at water depths shallower than 7 m prevented the germination of spores of deep water Laminariales from this region.

“…For this reason, a tight coupling exists between photosynthesis and nitrogen incorporation by phytoplankton (Dohler 1985, Turpin & Bruce 1990, Behrenfeld et al 1995, Goes et al 1995. As already demonstrated, damaging effects of UV radiation on photosynthetic electron transport (Melis et al 1992, Schofield et al 1995, Nilawati et al 1997 as well as on photosynthetic production of ATP (Vosjan et al 1990) and NADPH could alter the amount of energy available for nitrogen metabolism (Dohler et al 1987, Behrenfeld et al 1995, Dohler & Buchmann 1995. Recently, Goes et al (1994Goes et al ( , 1995Goes et al ( , 1996 demonstrated that the inhibition of photosynthesis by UV-B is accompanied by changes in the biosynthesis rates and composition of several biochemical compounds (fatty acids, monosaccharides and amino acids) in phytoplankton.…”

Section: Introductionmentioning

confidence: 98%

Effects of ultraviolet-B radiation on simultaneous carbon and nitrogen transport rates by estuarine phytoplankton during a week-long mesocosm study

Mousseau¹,

Gosselin²,

Levasseur³

et al. 2000

The effect of UV-B radiation on photosynthesis and nitrogen uptake by an estuarine phytoplankton community was investigated during a week-long experiment, conducted in 8 mesocosms under varying conditions of UV-B radation: reduced UV-B, natural radiation, and 2 levels of enhanced UV-B. Twice a day, dissolved inorganic carbon and total dssolved nitrogen (15N) transport rates were estimated simultaneously from in situ incubations. Irrespective of the treatment, phytopIankton biomass (chlorophyll a) and primary production increased over the first 3 d. Subsequently, nitrate and silicate depletion resulted in a decrease in algal biomass and productivity. Enhanced UV-B radiation was deleterious to chlorophyll a specific transport rates of C and N when compared to reduced and natural UV-B. The C:N transport ratios, as well as the P0C:PON ratios, were generally not affected by enhanced or reduced UV-B. In the enhanced UV-B treatments, carbon transport rates were often significantly higher in the afternoon than in the morning, suggesting that phytoplankton exposed to UV-B developed photoprotective mechanisms against UV radiation on a daily basis. A shift in the algal community assemblage from diatoms ( > l 0 pm) to small flagellates (5-10 pm) was observed during the study. Small flagellates were less sensitive to the UV-B treatments than diatoms, whose abundance decreased under reduced and enhanced UV-B. Results from this study suggest that UV-B exposure on a daily basis could change the chlorophyll a specific transport rates of C and N and alter the structure of the phytoplankton community.