Exposure of natural Antarctic marine microbial assemblages to ambient UV radiation: effects on bacterioplankton

Abstract

Seasonal ozone depletion over Antarctica leads to enhanced UVB (280 to 320 nm) radiation throughout the period of greatest biological production. The effect of UV radiation on bacterioplankton has received little attention, and its effects on marine microheterotrophs and viruses, which mediate bacterial biomass, are poorly understood. This study examined the impact of ambient solar W radiation on bacterioplankton in natural Antarctic microbial communities. Following a lag of 2 d, bacterial concentrations increased all light treatments. Inhibition of bacterial growth increased with increasing UV irradiance and duration of exposure, reaching 27 % inhibition in hlgh UV treatments (c2.0 m equivalent depth) compared to controls after 7 d exposure. Bacterioplankton growth rates declined in all treatments during post-UV incubation, particularly at lower UV irradiances (23.0 m equivalent depth), indicating UV-induced inhibition of bacterial mortality during irradiation. Positive bacterial growth coincided with both phytoplankton mortality and increased microheterotroph concentrations following exposure to high UV irradiances. Exposure of Antarctic microbial communities to ambient UV is likely to increase microbial respiration of carbon in surface waters and reduce vertical carbon flux.

The interaction of phytoplankton and bacteria in a high mountain lake: Importance of the spectral composition of solar radiation

“…Nevertheless, whereas these authors found this recovery at moderately low intensities of UVA and PAR, we only detected it at high light intensities (i.e., at upper depths). Our results were in line with the finding by Davidson and van der Heijden (2000) that bacteria in whole water were able to repair UV-induced damage and grow while residing in near-surface waters in Antarctic. In light of the above considerations, we conclude that the net effect of full sunlight (stimulatory or inhibitory) on bacterial activity at upper depths is the result of interplay between the detrimental effects of UVB and the recovery processes promoted by UVA and PAR.…”

“…Bacterial standing-stock parameters and bacterial production yielded values near the lower limit of the range reported (Reche et al 1996;Straskrabová et al 1999a;Davidson and van der Heijden 2000). Because our main objective was to evaluate the effect of spectral composition of solar radiation on the algae-bacteria relationship, mimicking the natural environment, we simultaneously exposed bacteria (in whole water) and [ 3 H]TdR to solar radiation in situ in our experimental approach.…”

“…As a consequence, short-term bacterial production would augment, establishing a coupled relationship between the two communities. This scenario would only be plausible if the detrimental effects of UVB and UVA on bacteria were counteracted by the beneficial effects of UVA and visible radiation (Kim and Sancar 1993;Kaiser and Herndl 1997;Davidson and van der Heijden 2000), thus allowing the enhancement of bacterial production due to this higher organic C availability.…”

Exposure of natural Antarctic marine microbial assemblages to ambient UV radiation: effects on the marine microbial community

“…The influence of UV radiation on the natural protist community was determined using aliquots of the same samples used to determine the previously published effect of UV on the bacterioplankton. For detailed methods of sample acquisition, preparation and incubation see Davidson & van der Heijden (2000).…”

Interactive effects of temperature and nutrient limitation on the response of alpine phytoplankton growth to ultraviolet radiation

“…Several studies have revealed that UVR can negatively affect the growth (Nilawati et al 1997;Davidson and van der Heijden 2000) and photosynthetic rates (Roos and Vincent 1998;Litchman et al 2002) of phytoplankton and can alter phytoplankton community composition (Karentz et al 1991;Cabrera et al 1997). However, a number of studies have also indicated a lack of effect of UVR on the growth rates of algae (Halac et al 1997).…”