Studies on productivity of Coffee. II – Effect of soil moisture on photosynthesis and transpiration of Coffea arabica

A study was made on the effect of soil water stress on transpiration, photosynthesis, stomatal aperture and relative turgidity of coffee plants. The decrease in turgidity as a consequence of soil moisture depletion was only small, due to the closing of stomatas and hence a decrease in transpiration. This means that an efficient water control is present in coffee plants. The reduction in photosynthesis, however, was much more pronounced than that in transpiration. This could be ascribed, apart from an increase in stomatal resistance, to the large effect of increasing leaf temperature on the internal C02 concentration. The diurnal variation in stomatal resistance and internal C02 concentration shows that at midday with a moderate soil moisture stress a closure of stomates results in a decrease in C02 internal. Net photosynthesis almost recovers in a period of five days when rewatering after drought.