Experimental measurements of leaf carbon isotope discrimination and gas exchange in the progenies of Plantago depressa and Setaria viridis collected from a wide altitudinal range.

Significant correlations between leaf carbon isotope discrimination (Delta) and altitude and between gas exchange and altitude have been reported in previous studies, raising the question of whether the altitudinal variations in discrimination and gas exchange can be attributed to genetic differences among populations from different altitudes. Studies that focus on in situ analysis cannot distinguish the effects of genetic variation from environmental variation. This article describes an experiment in which seeds of Plantago depressa (C3 species) and Setaria viridis (C4 species) collected from a wide altitudinal range were grown in the same environment. Carbon isotopic ratios (delta(13)C) and gas exchange of the seedlings were measured. The progenies of P. depressa and S. viridis no longer display any significant Delta decreases with the altitude of origin as seen in situ. Furthermore, photosynthetic rate, stomatal conductance, the ratio of intercellular to ambient CO(2) and intrinsic water use efficiency for P. depressa and S. viridis grown in the greenhouse are also not significantly related to the altitude of origin. The observations suggest that altitudinal variations in Delta and gas exchange are not because of genotypic differences, independent of photosynthetic type.