Interspecific variability of δ¹³C

Isotopic composition of carbon measured as d¹³C is an indicator of water-use efficiency Bonal et al. (2000) measured both d¹³C (‰) and leaf nitrogen concentration (%). Data were collected out on three sites: Paracou, Saint-Élie SLD and Saint-Élie DVD (see the soil studies comparison).

Unpublished data on ten more sites are available uppon request to the authors.

Data

Values by species.

Summary

Bonal et al. (2000)

The interspecific variability of sunlit leaf carbon isotope composition (δ¹³C), an indicator of leaf intrinsic water-use efficiency (WUE, CO₂ assimilation rate/leaf conductance for water vapour), was investigated in canopy trees of three lowland rainforest stands in French Guiana, differing in floristic composition and in soil drainage characteristics, but subjected to similar climatic conditions. We sampled leaves with a rifle from 406 trees in total, representing 102 species. Eighteen species were common to the three stands. Mean species δ¹³C varied over a 6.0 parts per thousand range within each stand, cornsponding to WUE varying over about a threefold range. Species occurring in at least two stands displayed remarkably stable δ¹³C values, suggesting a close genetic control of species, δ¹³C. Marked differences in species δ¹³C values were found with respect to: (1) the leaf phenology pattern (average δ¹³C=-29.7 parts per thousand and -31.0 parts per thousand in deciduous-leaved and evergreen-leaved species, respectively), and (2) different types of shade tolerance defined by features reflecting the plasticity of growth dynamics with respect to contrasting light conditions. Heliophilic species exhibited more negative δ¹³C values (average δ¹³C=-30.5 parts per thousand;) (i.e. lower WUE) than hemitolerant species (-29.3 parts per thousand). However, tolerant species (-31.4 parts per thousand) displayed even more negative δ¹³C values than heliophilic ones. We could not provide a straightforward ecophysiological interpretation of this result. The negative relationship found between species δ¹³C and midday leaf water potential (ψ_WM) suggests that low δ¹³C is associated with high whole tree leaf specific hydraulic conductance. Canopy carbon isotope discrimination (Δ_A) calculated from the basal area-weighed integral of the species δ¹³C values was similar in the three stands (average Δ_A=23.1 parts per thousand), despite differences in stand species composition and soil drainage type, reflecting the similar proportions of the three different shade-tolerance types among stands.