Diurnal decline in the photosynthetic capacity of uppermost leaves in an eggplant canopy grown in a horticultural greenhouse.

Abstract

Parameters representing leaf photosynthetic capacity, namely, the maximal carboxylation rate (V _cmax), maximal electron transport rate (J _max), and triose phosphate-utilization rate (T _p), can vary depending on various factors. The present study investigated diurnal variations in V _cmax, J _max, and T _p of uppermost leaves of soil-grown, well-watered eggplant in a greenhouse based on the simultaneous measurements of leaf gas exchange and chlorophyll fluorescence. The values of net photosynthetic rates and electron transport rates plotted against intercellular CO₂ concentrations were noticeably higher in the morning than in the afternoon. Significant differences were detected among the values of V _cmax, J _max, and T _p obtained at different times of day (08:30, 11:00, 13:30, and 16:00 h). All three parameters tended to decline as the time of day advanced; compared to the values at 08:30 h, V _cmax, J _max, and T _p declined by approximately 15% at 16:00 h. Among the three parameters, T _p appeared to be the most sensitive to time.