CONTROLS ON ISOPRENE EMISSION FROM TREES IN A SUBTROPICAL DRY FOREST

Isoprene emission from vegetation is the single most important source of photochemically active reduced compounds to the atmosphere. We pres ent the first controlled-environment measurements of isoprene emission from leaves of tropical forest trees. Our studies were conducted in t he Guanica State Forest in Puerto Rico. We report the effects of tempe rature and light variations on biogenic isoprene emissions during 1995 . Maximum emission rates varied among species from 0 to 268 nmol m(-2) s(-1). Values at the upper end of this range of maximum emission rate s are 23 times higher than values reported from any temperate taxa. Is oprene emission showed strong sensitivity to light and temperature var iations. In contrast to temperate plants, whose emissions tend to satu rate at a light intensity of approximate to 1000 mu mol m(-2) s(-1), e missions from the tropical species increased with light intensity up t o 2500 mu mol m(-2) s(-1). The temperature optima for emissions from t hese plants were similar to those previously reported for temperate pl ants: approximate to 40 degrees C. The high maximum emission rates and lack of light saturation indicate that estimates of isoprene emission from tropical forests need to be revised upwards.