SPATIAL DISTRIBUTIONS OF FOLIAR NITROGEN AND PHOSPHORUS IN CROWNS OF EUCALYPTUS-GRANDIS

Eucalyptus grandis trees were grown in plantations with and without added fertiliser to examine the effects of plant nutrition on photosynthesis and growth. Leaves were sampled from known locations within canopies of selected trees and leaf N and P concentrations were measured. Contour maps of N and P distributions were then produced for crowns of trees aged between 6 and 16 months. Gas exchange measurements on sample leaves were used to estimate parameters of a model of C3 photosynthesis as a function of leaf N and P concentrations. Linear relationships were obtained between model parameters and leaf N concentration, but P appeared to be present in excess, since no correlation was found with P concentration. Photosynthetic light response curves were calculated for model leaves with differing N concentrations. The curves show that optimal concentrations of N in leaves depend on mean levels of irradiance during growth.