Leaf structure and chemical composition as affected by elevated CO2: genotypic responses of two perennial grasses

Genotypic variability was studied in two Mediterranean grass species, Bromus erectus and Dactylis glomerata , with regard to the response to CO₂ of leaf total non-structural carbohydrate concentration (TNC]_lf), specific leaf area (SLA), and leaf carbon and nitrogen concentrations (C]_lf and N]_lf, respectively). Fourteen genotypes of each species were grown together on intact soil monoliths at ambient and elevated CO₂ concentrations (350 and 700 μmol mol⁻¹, respectively). In both species, the most consistent effect of elevated CO₂ was an increase in TNC]_lf and a decrease in leaf nitrogen concentration when expressed either as total dry mass N_m]_lf, structural dry mass N_mst]_lf or leaf area N_a]_lf. The SLA decreased only in D. glomerata , due to an accumulation of total non-structural carbohydrates and to an increase in leaf density. No genotypic variability was found for any variable in B. erectus , suggesting that genotypes responded in a similar way to elevated CO₂. In D. glomerata , a genotypic variability was found only for Cst], N_m]_lf, N_mst]_lf and N_a]_lf. Since N_m]_lf is related to plant growth and is a strong determinant of plant–herbivore interactions, our results suggest evolutionary consequences of elevated CO₂ through competitive interactions or herbivory.