Influence of temperature on the photosynthetic response of benthic diatoms : fluorescence based estimates

Abstract

The short-term effects of increasing temperature on the photosynthetic and photophysiological characteristics of benthic diatoms (Navicula sp., Nitzschia sp., Cylindrotheca closterium and Pleurosigma elongatum) were investigated by measuring the PSII-fluorescence kinetics of cultured specimens. Photosynthesis versus irradiance curves were measured at six temperatures (10, 15, 20, 25, 30 and 35°C) every two hours over twenty-four hours. For most of the species, the effective quantum yield of PSII (ΦPSⅡ) showed a reducing trend with increasing temperature. The relative maximum electron transport rate (rETRmax) was significantly stimulated by increasing temperature up to the optimum temperature, and then sharply decreased. Relative to the values of other parameters, the maximum light use coefficient (a) was insensitive and decreased significantly only under high temperatures (30 and 35°C). The light saturation index (EK) was quite similar to the rETRmax temperature response. With respect to the species' acclimation ability to temperature with time, Navicula sp. and C. closterium acclimated to a short-term change in temperature through their photophysiological adjustments. Pluerosigma elongatum, however, were not affected photophysiologically, due to parallel changes in the a and rETRmax. The PAM techniques are an useful way to study the physiological response of photoautotrophs, particularly, the influence of environmental factors such as temperature.