Fluorescence induction as a measure of photosynthetic capacity in marine phytoplankton: response of Thaiassiosira pseudonana (Baciliariophyceae) and Dunalielta tertiotecta (Chlorophyceae)

Abstract

The possibility was investigated of using in vivo chlorophyll fluorescence induction (time-scale ms) as an index of photosynthetic capacity in marine phytoplankton. Batch cultures of the diatom 73alassiosira pseudonana Hustedt (3H) and of the chlorophyte Dunaliella terfjolecta Butcher were preconditioned for 24 h at 8 different light intensities (2 to 60 W m-'). Photosynthetic rates at light saturation (P,) and the area above the fluorescence induction curve (ADcMu) were then determined; A , , , , was obtained using dark-adapted cells in the presence of 3-(3.4-dichloropheny1)-1,l-dimethyl-urea (DCMU), with a fluorometer having a shutter opening speed of about 0.3 ms. After 24 h, values of P, and of A,,,, were greater in the low than in the high irradiance cultures. In a second type of experiment, P, and ADC,, were measured throughout a 24 h incubation period after T pseudonana was shifted from 60 to 9 W m-' of irradiance. Both types of experiments showed a strong positive correlation between P, and A, , ,. The method offers the possibility of indexing the photosynthetic capacity of phytoplankton without lengthy incubation.