Short-term photosynthetic responses in the diatom Nitzschia Americana to a simulated salinity environment

Abstract

The effect of short-term variations in saiinity on photosynthesis and respiration in an estuarine clone of the diatom Nitzschia Americana was examined using a laboratory environmental simulation system. A computer-controlled culturing system simulated surface longitudinal salinity gradients in the Cape Fear River Estuary, NC by regulating the growth conditions of a continuous culture in real-time. Salinity changes were programmed based on a one-dimensional horizontal advection model of the Cape Fear River Estuary. The system proved useful in evaluating phytoplanklon photosynthetic responses to changes in its local environment on time scales similar to those operating in natural systems. As more sophisticated models of the physical environment and particle transport are incorporated into the simulation program, realistic physiological models of phytoplankton production can be developed. Average rates of net carbon fixation measured during the environmental simulation were compared to rates predicted by long-term adaptation studies. These results indicate that rates of net carbon fixation decline sharply following a rapid (hours) increase in salinity. Rates of net carbon fixation return, however, approximately to maximum predicted rates if the salinity environment is constant for approximately 24 h, suggesting an adaptation period. Presumably this time is necessary for N. Americana to initiate physiological mechanisms responsible for osmoregulation and various compensatory responses to changes in salinity. These results further indicate that significant errors may result when production models based on long-term adaptive responses are used to describe phytoplankton productivity in variable environments. © 1986 IRL Press Limited.