HIGH-RATES OF PHOTOSYNTHESIS IN THE TROPICAL PIONEER TREE, FICUS-INSIPIDA WILLD

Diurnal courses of CO2 and water-vapour exchange of canopy leaves of mature trees of Ficus insipida WILLD. (Moraceae) were studied under natural conditions in the tropical dry forest of Parque Metropolitano near Panama City, Republic of Panama. Measurements were conducted from early January 1993 (dry season) until July 1993 (wet season). Rates of net CO2 uptake were high throughout the study period, with up to 33.1 mu mol m(-2) s(-1) in the early dry season. During the dry season, gas exchange was characterized by strong reductions (''midday-depressions'') of net CO2 uptake and stomatal conductance at noon. However, daily carbon gain and diurnal water-use efficiency of CO2 uptake did not differ between seasons. East-exposed leaves that received direct sunlight during early morning hours showed higher CO2 uptake rates and lost less water per CO2 fixed than west-exposed leaves. As previously demonstrated for several canopy species from a tropical moist forest, the maximum rate of net CO2 uptake was a good predictor of daily carbon gain.