Temperature and Solar Radiation Interactions on 3H-leucine Incorporation by Bacterioplankton in a Subtropical Estuary

Although the effects of UV radiation are thought to be temperature independent, the photoinhibition of aquatic bacteria may be temperature dependent owing to enzymatic repair kinetics, an important consideration for climate change analyses. We examined the interactions between temperature and solar radiation in water samples collected from the Blackwater River, Pensacola Bay, and the coastal Gulf of Mexico (Florida) in July 2008. Subsamples were incubated in the dark for 20 h at either the in situ temperature, +5 degrees C from in situ or -5 degrees C from in situ after which they were amended with 3H-leucine and irradiated in full sunlight at their respective temperatures and compared to samples incubated simultaneously in the dark. Temperature and light significantly affected 3H-leucine incorporation at all locations and interactive effects between temperature and sunlight were found for Pensacola Bay and the Gulf. Generally, warmer waters reduced photoinhibition. The -5 degrees C treatment was always significantly more inhibited than the +5 degrees C treatment, but the in situ temperature and +5 degrees C and -5 degrees C treatments were not always significantly different. Photoinhibition reduction at warmer temperatures suggests specific effects on photobiology not observed in general cellular activity may be important in determining interactive ecosystem effects of climate change.