Distinguishing downregulation from other non-photochemical quenching of an Antarctic benthic macroalga using in situ fluorometry

Abstract

The quantum yield of chlorophyll a fluorescence of an Antarctic macroalga, Iridaea cordata, was measured in situ using logging fluorometers with an automated dark-acclimation capability throughout several diel periods. Application of far-red light and dark acclimation enabled the automated determination of photochemical quenching and non-photochemical quenching parameters that have until recently been restricted to manual measurement in terrestrial and shallow water environments. Our results show that non-photochemical quenching processes in Iridaea thalli that have been exposed to moderately high irradiances during the day, take all night to relax. We also show that, for algae exposed to relatively high light during the day, around 30–40% of total excitation flux is allocated to basal intrinsic non-radiative decay processes, with the remainder allocated to downregulation or photochemistry. The ability to evaluate the allocation of energy to these fundamentally different non-photochemical quenching processes has direct applications in assessing algal responses to both natural and anthropogenic stress. With this technology we open the door to a far more detailed examination of the regulation and kinetics of in situ photosynthesis and associated non-photochemical processes.