Effect of atmospheric CO2 enrichment on alfalfa (Medicago sativa L.) growth and nutrient status

The influence of increasing atmospheric CO2 concentrations on the growth and yield of alfalfa has been investigated by classic destructive techniques to assess the response of both above-ground biomass production and leaf area index, and by applying a foliar demography technique to the populations of leaves. The analysis of growth parameters showed that the above-ambient CO2 concentrations increase plant growth and yield during the whole period of CO2 enrichment. On the other hand, by the demographic technique, it was clear that increasing CO2 concentrations did not influence the age of the leaves forming the canopies, nor the intrinsic growth rate of the populations of leaves. The influence of CO2 enrichment on leaf mineral nutrients, mineral uptake and total non-structural carbohydrates (TNCs) content was also evaluated. Under high CO2 the observed stimulation of plant growth might be related to a leaf mineral nutrient dilution (except in the case of Zn). Mineral uptake per unit ground area increased, except in the case of Mg, Fe and Cu, and leaf TNCs content increased mainly as a result of a higher starch content