Transpiration Efficiency, Specific Leaf Weight, and Mineral Concentration in Peanut and Pearl Millet

Transpiration efficiency (TE) is the weight of dry matter produced per unit of transpiration. If mineral nutrients are taken up in proportion to transpiration, then the concentration of minerals in dry matter may be predictive of TE. It has recently been reported that specific leaf weight (SLW) is also correlated with TE. Since both mineral concentration and SLW are easily and inexpensively measured, they may be valuable predictors of TE. Five experiments with 7 to 19 genotypes of peanut (Arachis hypogaea L.; C3 species) and four experiments with 9 or 10 genotypes of pearl millet [Pennisetum glaucum (L.) R. Br.; C4 species] were conducted to assess the predictive value of mineral concentration and SLW for TE. In peanut experiments, samples were also analyzed for C isotope discrimination (Δ). Plants were grown in pots in the greenhouse in sand, soil, and solution culture. Specific leaf weight, Δ, ash, and mineral element concentrations were determined at the end of the experiments. There was a strong negative correlation between Δ and TE in the four peanut experiments in which Δ was determined. Leaf ash concentration was negatively correlated with TE in four out of six comparisons for each of the species (r = −0.55 to −0.88). In peanut, Ca and Mg were negatively correlated with TE. No other elements were consistently related to TE in either peanut or pearl millet. The SLW was positively correlated with TE. Thus, both leaf ash and SLW were predictive of TE, but further research is needed to determine the physiological bases for the relationships and their general applicability.