| Abstract: | We used a device called a Phototron to measure the effects of UV radiation on the cosmopolitan algae, Cryptomonas erosa, grown in continuous cultures. In the Phototron, we investigated changes in photosynthetic parameters (Pmax – specific production rate at optimal light intensity;  – initial slope of the linear portion of the Photosynthesis-Irradiance curve; and  – the convexity or rate of bending) and carbon allocation as a function of irradiance at three different environmentally-realistic doses of UV radiation in unconditioned (no prior UV exposure) and conditioned algae (15 d previous UV exposure). For unconditioned control algae, Pmax-Total was lower, although not significantly, than the two highest UV treatments. For conditioned control algae, Pmax-Total was higher, although not significantly, than all UV treatments. Our data suggest that short term (4 h) exposure to low levels of UV (8.09 W m–2 unweighted) does not affect Pmax-Total in C. erosa, but does change the proportion of carbon allocated to lipids and proteins. Also, comparisons of lipids, polysaccharides and proteins as a percent of total carbon uptake between unconditioned and conditioned algae indicate that exposure history to UV radiation can have a negative impact on carbon allocation to lipids and proteins, in a wetland alga species that is crucial to the efficient transfer of energy through freshwater food webs. |
