Differences in carbon isotope discrimination and whole-plant transpiration efficiency among nine Australian and Sahelian Acacia species

Abstract

We observed coordinated differences in water-use efficiency, 13 C isotope composition, and whole-plant transpiration efficiency among nine Acacia species, although the up scaling from leaf to whole-plant level resulted in different relationships in Sahelian and Australian species. The genus Acacia sensu lato contains a large variety of tropical to Mediterranean species adapted to habitats ranging from mesic to arid in Africa and Australia. We checked whether transpiration efficiency differed among a range of nine Sahelian and Australian species and whether it was related to the degree of aridity of the original area or to their type of foliage (pinnate leaves or phyllodes). Intrinsic water-use efficiency (W I) was recorded from leaf gas exchange and whole-plant transpiration efficiency (TE) from biomass production and water consumption of potted seedlings. Both W I and TE were compared to 13C discrimination (Δ13C) computed from either bulk foliage or extracted cellulose. At leaf level, Δ13C matched closely W I across species, while at the whole-plant level, the relationship between TE and either Δ13C or W I differed between the Sahelian and the Australian species. Large interspecific differences were found but they were not related to the aridity of the origin nor to the type of foliage. Δ13C captured well the variability of W I among several Acacia species while species differences in carbon-use efficiency (the fraction of carbon assimilated recovered in plant biomass) or the relative nocturnal transpiration may disrupt the relationship between TE and Δ13C.