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

Parameters representing leaf photosynthetic capacity, namely, the maximal carboxylation rate (Vcmax), maximal electron transport rate (Jmax), and triose phosphate-utilization rate (Tp), can vary depending on various factors. The present study investigated diurnal variations in Vcmax, Jmax, and Tp 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 Vcmax, Jmax, and Tp 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, Vcmax, Jmax, and Tp declined by approximately 15% at 16:00 h. Among the three parameters, Tp appeared to be the most sensitive to time.