High rates of photosynthesis in the tropical pioneer tree, Ficus insipida Willd.

Abstract

Summary Diurnal courses of CO 2 and water-vapour exchange of canopy leaves of mature trees of Ficus insipida W illd . (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 CO 2 uptake were high throughout the study period, with up to 33.1 μmol m − 2 S −1 in the early dry season. During the dry season, gas exchange was characterized by strong reductions (“midday-depressions”) of net CO 2 uptake and stomatal conductance at noon. However, daily carbon gain and diurnal water-use efficiency of CO 2 uptake did not differ between seasons. East-exposed leaves that received direct sunlight during early morning hours showed higher CO 2 uptake rates and lost less water per CO 2 fixed than west-exposed leaves. As previously demonstrated for several canopy species from a tropical moist forest, the maximum rate of net CO 2 uptake was a good predictor of daily carbon gain.