Dry-season leaf flushing of Enterolobium cyclocarpum (ear-pod tree): above- and below-ground phenology and water relations

Above- and belowground phenology and water relations of Enterolobium cyclocarpum Jacq. trees in the dry forest of Santa Rosa National Park, Costa Rica were studied during two consecutive phenological cycles, from November 1998 to June 2000. Aboveground phenological activity, including leaf shedding, growth and maturation of dormant fruits, new leaf flushing and flowering, occurred during the dry season. Measurements of leaf water potential, stomatal conductance and sap flow indicated that stomata of newly flushed leaves remained essentially closed until the onset of the first rains, suggesting that the main factor accounting for the favorable water balance of dry-season flushed leaves was their capacity to restrict water loss. Evidence of a contribution from stem and root water stores to shoot expansion was mixed because only the first dry-season flushing episode monitored was accompanied by a marked decrease in stem and root water potentials. Fine root production did not precede leaf flushing, occurred only after the onset of the rainy season and stopped under drought conditions, suggesting that soil water content was the most important variable controlling fine root dynamics in this species.