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

Abstract

Leaf gas exchange rates, predawn Ψ and daily minimum Ψ leaf water potentials were measured during a wet-to-dry season transition in pioneer (Jacaranda copaia, Goupia glabra andCarapa guianensis) and late stage rainforest tree species (Dicorynia guianensis andEperua falcata) growing in common conditions in artificial stands in French Guiana. Carbon isotope discrimination (Δ) was assessed by measuring the stable carbon isotope composition of the cellulose fraction of wood cores. The Δ values were 2.7‰ higher in the pioneer species than in the late stage species. The calculated time integratedC values derived from the Δ values averaged 281 μmol mol in the pioneers and 240 μmol mol in the late stage species. The corresponding time-integrated values of intrinsinc water-use efficiency [ratio CO assimilation rate (A)/leaf conductance (g)] ranged from 37 to 47 mmol mol in the pioneers and the values were 64 and 74 mmol mol for the two late stage species. The high Δ values were associated-at least inJ. copaia-with high maximumg values and with high plant intrinsinc specific hydraulic conductance [C≔g/(Ψ-Ψ], which could reflect a high 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 Δ for distinguishing ecophysiological functional types among rainforest trees.

Water acquisition patterns of two wet tropical canopy tree species of French Guiana as inferred from H218O extraction profiles

“…Potentially, there can be much greater competition for water and nutrient resources in the upper soil horizons. However, shallow-rooted species as D. guianensis might develop adaptive mechanisms such as partial [28,29,30,34] or total [7] stomatal closure to tolerate or avoid soil drought, as confirmed by the lack of effect of either soil drainage type or seasonal soil moisture deficit on Ψ wm in D. guianensis. It must be recalled here that D. guianensis has a high water-use efficiency as compared to other canopy tree species in French Guiana [9].…”

“…Tropical canopy rainforest tree species have been found to strongly differ in intrinsic water-use efficiency, defined as the ratio of CO 2 assimilation to leaf conductance to water vapour (A/g s ) and to seasonal soil drought sensitivity [7,9,27,28,29,30,34]. Several characteristics have been proposed to explain these differences, among which, differences in CO 2 assimilation rates [1,6,7,29], stomatal regulation [7,9,23,26,29] or hydraulic conductivity [9,39,41].…”

“…Several characteristics have been proposed to explain these differences, among which, differences in CO 2 assimilation rates [1,6,7,29], stomatal regulation [7,9,23,26,29] or hydraulic conductivity [9,39,41]. Differences in water acquisition strategies among species and the ability of some species to explore deep soil layers could also explain these differences.…”

“…Differences in water acquisition strategies among species and the ability of some species to explore deep soil layers could also explain these differences. For instance, Huc et al [29] suggested that differences in stomatal sensitivity to seasonal soil drought between pioneer and late stage canopy tree species might be related to differential soil water extraction depth, late stage species being able to explore deeper soil layers. Alexandre [1] observed that a strong and deep taproot in some canopy tree species allowed them to extract water in deeper layers and to avoid seasonal drought stress.…”

“…It is hypothesised that (1) E. falcata may develop a deep rooting system which allows avoidance of seasonal soil drought stress [5,7,29,30], (2) …”