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.
Nicholson and Simmonds seems to be thought provocative and its conclusion could be a controversial one. In order to shed more light on the subject matter, the Technical Editor decided to make a onetime exception to the rule of no printed discussions on Brief Notes. Based upon the recommendations by the authors and the Associate Editor who processed this Note, a number of prospective discussers were contacted and they were encouraged to send in their discussions. Those received are published below in the order of receipt. The authors have prepared a Closure/Since other readers may also have comments to make on this Note and since it is only proper that the waive of the rule should be also available to them, further discussions will be accepted by the Technical Editor until September 1,1977. The Technical Editor must, however, reserve the right to decline any discussion or delete a part of a discussion if the point raised has been brought out previously.
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