Growth and Biomass Partitioning in Eucalyptus grandis Seedlings in Response to Nitrogen Supply

Seedlings of Eucalyptus grandis were grown using an aeroponic culture technique in which continuously circulating solution was sprayed over seedling roots. Nutrient solutions, made up so that nitrogen was the element limiting growth, were added hourly at relative addition rates between 0.04 and 0.12 d-1. This technique enabled stable seedling nitrogen concentrations and relative growth rates to be maintained during experimental periods of 40-80 days in most treatments. Once steady state growth was established, allocation of dry matter to stems compared with foliage increased with ontogeny and the allometric relationship was not influenced by plant nitrogen status or genotype. In contast, the intercept of the allometric relationship between root mass and foliage mass was dependent on plant nitrogen concentration, but the slope was equal to unity at all nitrogen concentrations. Our data indicate that nitrogen-induced changes in allocation of dry matter between foliage and root components, together with changes in specific leaf area, had a larger influence on seedling growth rate than did changes in net rate of carbon gain per unit leaf area.