Studies on productivity of coffee. I. Effect of light, temperature and CO2 concentration on photosynthesis of Coffea arabica

A study was made on the effect of light and temperature on net photosynthesis, growth and transpiration of Coffea arabica. Net photosynthesis was described as a diffusive process depending on a carbon dioxide gradient and an overall resistance. At a relative low temperature (24 °C), the effect of light on net photosynthesis was comparable with that of most annual agricultural crops. Calculated internal concentration and overall resistance at 0.3 cal cnr2 min-1 were zero p.p.m. and 15 sec cm'1 respectively. Above this temperature each degree rise resulted in an increase of 20 p.p.m. in internal C02 concentration.This effect alone accounts already for a decrease in dry matter production of approximately 7% per degree centigrade. The increase in internal C02 was accompanied with an increase of the overall resistance, reducing still more the dry matter production. Low rates of photosynthesis in coffee reported in literature could be explained. Increasing the external C02 content and thus the C02 gradient had only a minor effect on photosynthesis. The effect of temperature and light on growth confirmed the conclusions of net photosynthesis research. Since both factors increase transpiration substantially, the water use efficiency decreases strongly with an increase in light and in temperature above 24 °C. The results may have importance for selecting optimum growth conditions for coffee.