Pioneer and late stage tropical rainforest tree species (French Guiana) growing under common conditions differ in leaf gas exchange regulation, carbon isotope discrimination leaf water potential

Leaf gas exchange rates, predawn (Psi(wp)) and daily minimum (Psi(wm)) leaf water potentials were measured during a wet-to-dry season transition in pioneer (Jacaranda copaia, Goupia glabra and Carapa guianensis) and late stage rainforest tree species (Dicorynia guianensis and Eperua falcata) growing in common conditions in artificial in French Guiana. Carbon isotope discrimination (Delta) was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The delta values were 2.7 per mil higher in the pioneer species than in the late stage species. The calculated time integrated C(i) values derived from the Delta values averaged 281 micromol per mol the pioneers and 240 micromol per mol in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency (ratio CO2 assimilation rate (A)/leaf conductance (g)) ranged from 37 to 47 mmol per mol in the pioneers and the 64 and 74 mmol per mol for the two late stage species. The high Delta value associated - at least in J. copaia - with high maximum g values and with high plant intrinsinc specific hydraulic conductance (C=g/(Psi(wp) - Psi(wm)) which could reflect competitive ability for water and nutrient uptake in the absence of soil drought in the pioneers. A further clear discriminating trait of the pioneer species was the very sensitive stomatal response to drought in the soil, which might be associated with a high vulnerability to cavitation in these species. From a methodological point of view, the results show the relevance of Delta for distinguishing ecophysiological functional types among rainforest trees.