In situ monitoring of chlorophyll fluorescence to assess the synergistic effect of low temperature and high irradiance stresses inSpirulina cultures grown outdoors in photobioreactors

Abstract

A chlorophyll fluorescence technique was applied to an in situ study on the effects of low temperature and high light stresses on Spirulina cultures grown outdoors in controlled tubular photobioreactors at high (1.1 g L- 1 ) and low (0.44 g L -1 ) biomass concentrations. Diurnal changes in PSII photochemistry (F v /F m ) after 15 min of darkness, or in the light (dF/F' m ), and non-photochemical (qN) quenching were measured using a portable, pulse-amplitude-modulated fluorometer. The depression of the F v /F m ratio of Spirulina cultures grown outdoors at 25°C (i.e. 10°C below optimum for growth) and 0.44 g L -1 , reached 30% at the middle of the day. At the same time of the day the dF/F' m ratio showed a reduction of up to 52%. The depression of both F v /F m and dF/F' m was lower in the cultures grown at 1.1 g L -1 . Photoinhibition reduced the daily productivity of the culture grown at 0.44 g L -1 and 25°C by 33% with respect to that grown at 35°C. Changes in the growth yields of the cultures grown under different temperatures and growth rates correlate well with analogous changes in photon yield (dF/F' m ). Simple measurements of photochemical yield (F v /F m ) can be used to test the physiological status of Spirulina cultures. The results indicate that the saturating pulse fluorescence technique, when used in situ, is a powerful tool for assessment of the photosynthetic characteristics of outdoor cultures of Spirulina.