An inter-basin comparison of nutrient limitation and the irradiance response of pulse-amplitude modulated (PAM) fluorescence in Lake Erie phytoplankton |
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Authors: | K. J. Rattan |
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Affiliation: | 1. Department of Biology, University of Waterloo, 200 University Ave. W., Waterloo, ON, N2L 3G1, Canada 2. Environment Canada, 867 Lakeshore Ave. W., P.O. Box 5050, Burlington, ON, L7R 4A6, Canada
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Abstract: | This research examined the application of the maximum quantum efficiency (F v/F m) and relative electron transport rate versus irradiance curves (rETR) as a rapid, sensitive assessment of Lake Erie phytoplankton nutrient status. I evaluated the potential benefits of the variable fluorescence parameters by comparing these parameters with chemical and physiological nutrient status assays. I tested the hypothesis that F v/F m and rETR curves could diagnose nutrient status in natural lake phytoplankton and be capable of discriminating which inorganic nutrient is limited temporally and spatially. F v/F m was on average highest in the more eutrophic west basin (WB) and lowest in the more oligotrophic central basin (CB). According to the chemical and physiological indicators, P deficiency was most severe in the CB during summer stratification and N deficiency was strongest in the WB during isothermal conditions. Like F v/F m, rETR at light saturation (rETRmax) and the initial slope of the rETR versus irradiance curve (α) decreased as the severity of N and P deficiency increased. Amendment with N or P stimulated increased F v/F m, rETRmax, and α in N- and P-limited samples, respectively, and abolished the photoinhibition apparent in rETR curves of nutrient-limited samples. These results supported the view that the N and P deficiency assays, and corresponding variations of variable fluorescence parameters, were valid indicators of widely variable N and P deficiency in the phytoplankton, and could be used to provide a promising tool in determining phytoplankton nutrient status. Contrary to my hopes, it did not appear that rETR–irradiance curves could discriminate between N and P deficiency. Identification of the most limiting nutrient still demanded additional information beyond the variable fluorescence measurements. |
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