JPR Advance Access published online on August 5, 2008
Journal of Plankton Research, doi:10.1093/plankt/fbn083
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Bacterioplankton and Phytoplankton Production Rates Compared at Different Levels of Solar Ultraviolet Radiation and Limiting Nutrient Ratios
Department of Biology University of Mississippi Oxford, Mississippi 38677, USA
CORRESPONDING AUTHOR E-mail: byochs{at}olemiss.edu
Received on March 13, 2008; revised on July 28, 2008; accepted on August 1, 2008
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Abstract |
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In aquatic environments in which nutrient concentrations are low, bacteria and phytoplankton may compete for the same nutrient resources. The degree and outcome of this interaction will depend partly on the relative efficiencies with which co-occurring organisms assimilate the limiting nutrient and produce new biomass. Any factor that affects differentially production rates of competing organisms could influence the competitive outcome. One such factor, which is likely to be relevant in sunlit environments, is ultraviolet radiation (UVR). We conducted a lakewater mesocosm experiment to test the effects of UVR in environments of varying carbon+nitrogen (C+N) and phosphorus+nitrogen (P+N) concentrations and ratios on volumetric production of bacterioplankton and phytoplankton. Over the course of the seven-day experiment, only with P+N addition did UVR have a significant effect on bacerioplankton, reducing bacterioplankton by 21%. UVR also significantly reduced phytoplankton with P+N addition, by up to 45%. For both bacterioplankton and phytoplankton the stimulatory effect of P+N addition was more than two-fold inhibition due to UVR exposure. Interaction effects of UVR and the nutrient environment were evident for both bacterioplankton and phytoplankton. Overall, the negative effect of UVR on bacterioplankton was less than on phytoplankton in mesocosms in which production was stimulated by nutrients. These results suggest that, at the level of the system, with nutrient addition, UVR provided a competitive advantage to bacterioplankton. Assessments of current or future effects of UVR on aquatic ecosystems require that combined effects of UVR exposure and nutrient availability on ecological interactions be fully considered.
Key Words: plankton • ultraviolet radiation • freshwater ecosystems • nutrient competition
Communicating Editor: Dr William Li
* Present address: National Water Research Institute Environment Canada 11 Innovation Blvd., Saskatoon, SK S7 N 3H5, Canada
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