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

Acknowledgments : This study was supported by a Cabinet Office grant-in-aid, the Advanced Next-Generation Greenhouse Horticulture by IoP (Internet of Plants), Japan, and JSPS KAKENHI grant numbers JP21K14946 and JP22H02468. The authors thank Nana Miyatake and Chiyuki Yamanaka for assisting with the measurements. Conflict of interest : The authors declare that they have no conflict of interest. representing photosynthetic capacity, namely, the maximal carboxylation maximal electron transport 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 CO 2 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.