Gas exchange rates and plant water potentials of Capsicum annuum L. under stressed and well watered conditions. Diurnal response patterns

Yolo Wonder pepper seedlings were grown in Policoro (Southern Italy) and maintained regularly irrigated until the beginning of flowering. Water was then withheld in the stressed treatment while the well irrigated one was watered every 25 mm of maximum evapotranspiration.Gas exchange measurements were performed on single plants in daily cycles (at 08.30, 10.30, 12.30, 15.00, 17.00 hrs) at various intervals along the crop cycle. Subsequently, water use efficiency (WUE) was calculated as the ratio between net canopy photosynthesis (NCP) and transpiration. Following the final measurement for the day, plants were harvested for green leaf area and dry matter determinations. Pre-dawn and daytime leaf water potentials were measured with a Scholander-type pressure chamber.NCP rates were comparable to those reported for crops other than vegetables, while transpiration rates were lower. In the stressed treatment, NCP following 10.30 hr increasingly lowered as the season progressed, while in the wet treatment decreasing activities were noticed following 12.30 hr later in the season.NCP approached a plateau in the control at a LAI value of 1.8, although the plants kept growing until a LAI of 3.4 was reached at the final sampling date. Stressed plants reached an earlier plateau (LAI=1.2), at a size close to the final one (1.6).The WUE, mean of the whole season, was higher in the wet (9.65 ± 0.61) than in the dry treatment (6.92 ± 0.65), and not significantly related to LAI.