PHOTOSYNTHETIC PERFORMANCE OF 2 COFFEE SPECIES UNDER DROUGHT

Coffea arabica cv. Red Catuai and C. canephora cv. Kouillou were grown in pots beneath a plastic shelter. When they were 14 months old, irri gation was withheld until the leaf pre-dawn water potential was about -1.5 and -2.7 MPa (designated mild and severe water stress, respective ly). Under mild stress, net photosynthetic rate (P-N) decreased mainly as a consequence of stomatal limitations in Kouillou, whereas such de creases were dominated by non-stomatal limitations in Catuai. Under se vere drought, further decreases in P-N and apparent quantum yield were not associated to any changes in stomatal conductance in either culti var. Decreases were much more pronounced in Catuai than in Kouillou, t he latter maintained carbon gain at the expense of water conservation. In both cultivars the initial chlorophyll (Chl) fluorescence slightly increased with no changes in the quantum efficiency of photosystem 2. In response to rapidly imposed drought, the Chl content did not chang e while saccharide content increased and starch content decreased. Pho toinhibition and recovery of photosynthesis, as evaluated by the ratio of variable to maximum fluorescence and by the photosynthetic O-2 evo lution, were unaffected by mild drought stress. Photoinhibition was en hanced under severe water deficit, especially in Catuai. In this culti var the O-2 evolution did not resume upon reversal from photoinhibitio n, in contrast to the complete recovery in Kouillou.