Transpiration Ratio and Plant Mineral Content Are Related Among Genotypes of a Range of Species

Abstract

The relationship between transpiration ratio (R, ratio of water transpired to carbon fixed) or cabon isotopic discrimination (Δ) and leaf dry-matter mineral content (m) was examined within several C₃ species including monocot and dicotyledonous species (Triticum aestivum, Hordeum spontaneum, Helianthus annuus and Nicotiana tabacum) and the C₄ species, Sorghum bicolor. In all species, whether grown in the glasshouse or in the field, m was positively correlated to R; consistently, m was positively correlated to Δ in the C₃ species, and negatively in sorghum.

These genetic correlations between transpiration ratio and mineral content contrast with the absence of such a relationship when variations of R were environmentally induced by changes of atmospheric humidity or carbon dioxide concentration. In those circumstances, and consistent with earlier reports, ash content or its major constituents were remarkably stable and insensitive to a doubling or more of R.

The genetic relationships shown in the present study are to some extent brought about by variations in assimilation and transpiration rates per se (i.e. passive mineral uptake), but the data indicate that they involve other quantitatively more important mechanisms, some of which may be related to the control of leaf water content. With the exception of Hordeum spontaneum, potassium was the element contributing the most to the relationship between R, or Δ, and mineral content. Depending on the species other elements showed a significant correlation with R or Δ. Further experiments are needed to unravel the nature of the genetic association between R and m. Meanwhile plant mineral content may be a useful criterion in selection programs to improve transpiration efficiency since its correlation with R was not much lower than that of carbon isotope discrimination.