Photosynthesis of Coffea arabica after chilling

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Abstract
Net photosynthetic CO2 exchange of 1‐year‐old plants of Coffea arabica L. was studied after the above‐ground parts had been exposed once or repeatedly to night temperatures in the chilling range. Chill‐reduced rates of CO2 uptake (measured at 24°C and at natural CO, level) were observed after a 12 h night exposure to about 6°C. After exposure to 4°C, activity was reduced to less than half of that of the controls, and after exposure to 0.5°C the leaves suffered visible necrotic injury and were no longer able to take up Co2 If the leaves were not lethally injured, net photosynthesis recovered completely within 2 to 6 days. About 25% of chill‐induced reduction of CO2 uptake was due to reduced stomatal aperture and 75% to impairment of carboxylation efficiency.Chilling on successive nights at 4–6°C reduced CO, uptake progressively on each day following treatment. After 10 nights, activity was decreased to less than 10% of initial performance. Conditioning at temperatures slightly above the chilling level (e.g. 15/I2°C) for 2 weeks led to almost complete impairment of photosynthetic activity without additional chilling stress instead of improving chilling tolerance.