Evaluating Leaf Ash Content and Potassium Concentration as Surrogates of Carbon Isotope Discrimination in Grassland Species

Abstract

Leaf ash content and potassium (K) concentration were evaluated as surrogates of carbon isotope discrimination (Δ) of the dominant species in an upland grassland in a 3‐year experiment. Previous results reported positive correlations between Δ and ash content or mineral concentrations, attributing this relationship to the passive accumulation, through the transpiration stream, of minerals in the vegetative plant parts. We found only a weak positive correlation between Δ and ash content or K concentration in 1997 (r=0.79, P < 0.05 and r=0.77, P < 0.05, respectively). No significant correlation was found between the traits in 1998 and 1999. When four of the seven most abundant species ( Poa pratensis , Lolium perenne , Festuca valida and Taraxacum officinale ) were grown under different treatments (mixed sward, monoculture, and nitrogen and P additions in mixed sward), a curvilinear relationship between Δ and ash content or K concentration was evident. Thus, our findings suggest that leaf ash content and K concentration cannot serve as surrogates of carbon isotope discrimination (Δ). Small genotype × environment interactions were reported for the three traits measured; the interactions were smallest for ash content. A positive correlation between leaf ash content and soil water content (at 5 and 15 cm depth) was found for four species ( P. pratensis , L. perenne , F. valida and Achillea millefolium ) and for the community as a whole. No significant correlation was found between leaf K concentration and soil water content.