EFFECT OF WATER-STRESS ON PHOTOSYNTHESIS, LEAF CHARACTERISTICS AND PRODUCTIVITY OF FIELD-GROWN NICOTIANA-TABACUM-L GENOTYPES SELECTED FOR SURVIVAL AT LOW CO2

Dry mass production, leaf characteristics and diurnal photosynthesis of two N. tabacum L. genotypes selected for survival at low CO2 and the parent Wisconsin-38 (control plants) were measured on water-stressed and well-watered plants in the field. Differences in photosynthesis per unit leaf area were small and not significant between genotypes, but different patterns of photosynthesis were observed in stressed and non-stressed plants, with water stress reducing total net carbon fixation by 45% in all genotypes. More dry mass was produced by the selected genotypes than by Wisconsin-38 under irrigation. Production was smaller and the same for all three genotypes when stressed. The increased dry mass of the selected genotypes was related to greater total leaf area per plant which was accompanied by more cells per unit leaf area but smaller cell volume than in the control plants. The decrease in dry mass production under water stress was related to a decrease in total leaf area per plant and a decrease in cell number per unit leaf area; however, cell volume increased.