PHOTOSYNTHESIS AND SUCCESSIONAL STATUS OF SEEDLINGS IN A TROPICAL SEMIDECIDUOUS RAIN-FOREST IN NIGERIA

(1) This study tests the hypothesis that photosynthetic performance of seedlings in a tropical forest depends on the successional status of the species. According to this hypothesis, pioneers display an enhanced capacity to utilize the high photon flux density associated with a gap. (2) Data were collected from nine species representing three ecological groupings: weeds of gaps, pioneer trees and climax trees. Pioneer trees had photosynthetic attributes similar to weeds. Compared to climax trees, both groups had higher stomatal conductances, higher light compensation points, higher rates of dark respiration, much higher mesophyll conductances, and often higher quantum efficiencies. (3) In a fluctuating light regime, there was no support for the hypothesis that species growing in shade show rapid stomatal responses to sunflecks, all species showed fluctuating rates of photosynthesis with little or no adjustment of stomata during the 20-min test.