FACTORS DETERMINING THE MIDDAY DEPRESSION OF PHOTOSYNTHESIS IN SMALL CARDAMOM (ELETTARIA CARDAMOMUM MATON) UNDER SUMMER CLIMATE

Abstract

Gas exchange and chlorophyll fluorescence quenching analysis were carried out on sunny days during summer to investigate the environmental and physiological factors limiting carbon gain in small cardamom canopies. Leaf net photosynthetic rate showed a unimodal diurnal pattern and midday depression of photosynthesis was observed at 12:00 h. Depression in photosynthesis at midday was mostly attributed to significant reductions in stomatal conductance and increase in intracellular CO2concentration. Midday depression in photosynthesis was found to be associated with decrease in maximum PSII efficiency (Fv/Fm) (reversible inactivation of photosystem II reaction centers) and increases of minimal fluorescence (Fo) in response to the high light intensity (PPFD). It is concluded that the decline of leaf stomatal conductance (gs) and reversible inactivation of photosystem II reaction centers under high light intensities in summer is an important factor contributing to midday depression of photosynthesis in small cardamom