Effect of night chilling on photosynthesis of two coffee species grown under different irradiances

The effect of night chilling on the photosynthetic physiology of seedlings of two coffee species (Coffea arabica L. and C. liberica Bull.) was investigated. The coffee seedlings were grown in pots in a fully-open site, and in a shade plot of 50% daylight for both coffee species, and in shade plots with two additional irradiance regimes of 8% and 25% daylight for C. liberica. In January 2003, the seedlings were moved to a cold storage room at 4degreesC overnight for three consecutive nights and returned to their original places during the day. Gas exchange rates were measured in the late morning, and chlorophyll a fluorescence was measured at dawn and mid-aftemoon during the day before chilling and the 3 d with the chilling treatment and the subsequent 3 d after chilling. Chlorophyll, carotenoid and MDA (malondialdehyde) contents were determined from the leaves of the coffee seedlings on the day before and the third day with the chilling treatment. The results showed that night chilling induced rapid decreases of gas exchange rates and decrease of maximum photochemical efficiency of photosystem II (F-v/F-m), and increases of both minimum fluorescence yield (F-o) and non-photochemical quenching (NPQ) for both species; these decreases and increases were usually stronger in seedlings grown in higher irradiances. The decrease of F-v/F-m and increase of F-o were stronger in C. liberica than in C. arabica. C. arabica reached significantly greater NPQ values than C. liberica. Night chilling decreased chlorophyll content and increased the carotenoid to chlorophyll ratio and MDA content in both species under all irradiances. After termination of the chilling treatment, the recovery of gas exchange rates, F-v/F-m and F-o were much quicker in C. arabica than in C. liberica. These results showed that night chilling induced a more severe photoinhibition, and its recovery was slower in C. liberica than in C. arabica. This is consistent with the distribution of the two species: C. liberica is cultivated in tropical lowlands, while C. arabica is cultivated at higher elevations. Shading significantly alleviated chilling-induced photoinhibition.