WATER-USE EFFICIENCY OF 10 TAXA OF OPUNTI A ESTABLISHED IN THE ARID MEDITERRANEAN REGION OF CHILE

One of the most important problems for terrestrial plants is to avoid the dehydration. The plants are faced to the dilemma of opposite prior ities: to maintain their stomata open forh fixing the CO2 and to avoid the water loss. This problem is analyzed in regard to the water use e fficency (WUE), wich is defined as the rate of CO2 assimilation in con nection with the water loss by transpiration. Water use efficiency was measured at different times: daily and seasonally, on introduced spec ies of Cactaceae grown in the Chilean arid region at two levels of ava ilable water. Among the platyopunties, a great variability of WUE data at the inter-specific levels is showed, daily WUE data vary between 3 6 und 83 mg DM/g H2O and seasonally between 19 and 54 mg DM/gH(2)O. Th ese results allow to establish a relation between WUE and photosynthet ic systems but equally, show the independance of these parameters to h ydric constraint.