CO2 GAS-EXCHANGE AND WATER-UPTAKE OF SWEET-PEPPER PLANTS UNDER THE CONDITIONS OF WATER-STRESS

As basis for the development of strategies, to control microclimate in greenhouse and to prevent water stress, CO2 gas exchange and water up take as well as leaf temperature of sweet pepper plants were measured in an air-conditioned chamber unter different conditions. The plants ( cv. 'Bellamy' and 'Mazurka') were cultivated in greenhouse. They had leaf areas from 22 to 54 dm(2), when measurements were carried out. Tw o treatments, a low and a high air temperature (T1 approximate to 25 d egrees C and T2 approximate to 35 degrees C), were tested with irradia nces between 0 and 2500 mu mol m(-2) s(-1) and vapour pressure deficit s between 7 and 41 hPa. Wilting of the leaves in the upper third of th e plant was observed at temperature level T2 and irradiances > 1500 mu mol m(-2) s(-1). On the top of the plants in average the leaf tempera ture laid about 5 K under the air temperature for the condition T2. Sm all differences in CO2 gas exchange were observed between both tempera ture levels. On the other hand a strong Influence of temperature on wa ter uptake was observed. For irradiances of 1000 mu mol m(-2) s(-1) a doubling of water uptake could be observed, when T2 was setted instead of T1. From this follows a drastic reduction in water use efficiency of dry matter production through temperature increase. With temperatur e level T1 the mean water use efficiency was 5.2 mu mol mmol(-1), wher eas it was 2.6 mu mol mmol(-1) for T2. The importance of temperature i nfluence on leaf conductance and transpiration to modelling was discus sed.