Influence of Temperature and Light on Rates of Inorganic Nitrogen Transport by Algae in an Arctic Lake

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Abstract
N-15 tracer techniques were used to assess the individual effects of temperature and light on maximum rates of dissolved inorganic N (DIN) transport by phytoplankton in an arctic lake. Transport rates of NO3- and NH4+ as a function of temperature in the range 3-30.degree. C were adequately described by 2nd- or 3rd-order polynomial functions. The optimum temperature for DIN transport was greater than the ambient water temperature by as much as 13.degree.. Transport at the ambient water temperature averaged only 55-60% of optimum. Mean temperature coefficients (.hivin.X .+-. SD) for NO3- and NH4+ transport in the temperature range > 0.degree.-15.degree. C were 2.3 .+-. 0.5 and 2.4 .+-. 0.3. The ratio of dark to light-saturated DIN transport (.rho.D/.rho.L) was used as a measure of light dependence in maximum rates of DIN transport. Values of (.rho.D/.rho.L (.hivin.X .+-. SD) for NO3- and NH4+ were 0.15 .+-. 0.09 and 0.41 .+-. 0.11, indicating a stronger light dependence for NO3- than NH4+ transport. In cases where dark NO3- transport was negligible, light was treated as a substrate and the Michaelis-Menten relationship fitted to the data. The half-saturation constant for light intensity in maximum NO3+ transport ranged from 7-29 .mu.E .cntdot. m-2 .cntdot. s-1, which was 6-31% of the photosynthetically active radiation at the lake surface.