Effect of Different Water Supply on Transpiration and Water Use Efficiency of Leek and Sweet Pepper

This study evaluated the effect of water supply on some physiological processes of leek (Allium porrum L. 'Giante Suito') and pepper (Capsicum annuum L. 'Slavy F1') plants, at two different irrigation levels: 1. optimal water supply: available water content (AWC) decreased below 65%; 2. drought stress: AWC decreased below 45%. Transpiration, photosynthetic activity and water use efficiency was measured by a portable infrared gas exchange analyzer (LCpro+). The first vegetation period (2010) was characterized by lower average temperature, higher air humidity, and less sunny hours than the second period (2011). In the case of pepper, in the first part of the vegetation period transpiration was more intensive under stress condition. However, in the second part the average transpiration of stressed plants was lower than that of plants under optimal water supply. The transpiration of leek was more intensive in the optimal irrigation treatment than under drought stress. The highest average transpiration of pepper and leek was similar (pepper: 2.01, leek: 1.97 mmol m(-2) s(-1)). For both species the negative effect of drought stress on photosynthetic activity was observed on most measuring dates. The highest difference between the photosynthetic rate values in stress and optimal water supply was observed in leek, in the last measuring date of 2011 (optimum: 5.56, stress: 2.60 mu mol m(-2) s(-1)). Water use efficiency (WUE) of leek leaves was higher under stress in the second part of season in 2010, and in whole season in 2011. In case of pepper the positive effect of drought stress on the WUE was observed only in the second (warmer and dryer) experimental year.