OIL PALM WATER STATUS IN RESPONSE TO DROUGHT IN COSTA-RICA

Adult oil palms grown on a sandy soil with no irrigation during the dr y season suffered from severe premature drooping of the lower leaves, a substantial accumulation of unopened leaves ("spears") and low stoma tal conductivity (C.) when compared to irrigated oil palms. Curiously, non-irrigated adult oil palms (11 and 17 years) revealed leaf water p otential (LWP) and relative water content (RWC) values equal to or gre ater than those of irrigated palms. The negative correlation observed between C and LWP, measured at midday on adult palms, is unusual on cu ltivated plants and indicates strong stomatal control of leaf water st atus, which enables the species to survive long drought periods. Young oil palms (10 months after planting out) did not succeed in maintaini ng a high leaf water status under severe drought conditions, probably because they did not have a voluminous stem and their root system was not very extensive. After 75 days of uninterrupted drought, on young o il palms exposed to drying out, the RWC and the LWP values measured at midday were lower than on oil palms with a good water supply.