Model simulations of spatial distributions and daily totals of photosynthesis in Eucalyptus grandis canopies

Abstract

A simulation model for radiation absorption and photosynthesis was used to test the hypothesis that observed nonuniform distributions of nitrogen concentrations in young Eucalyptus grandis trees result in greater amounts of daily assimilation than in hypothetical trees with uniform N distributions. Simulations were performed for trees aged 6, 9, 12 and 16 months which had been grown in plantations under a factorial combination of two levels of fertilization and irrigation. Observed leaf N distribution patterns yielded daily assimilation rates which were only marginally greater (2 mol⁻¹ N) were 60% higher for unfertilized than for fertilized trees at low levels of absorbed photosynthetically active radiation (PAR). Nitrogen use efficiency was dependent on fertilizer treatment and on the amount of absorbed PAR; NUE declined with increasing absorbed PAR, but decreased more rapidly for unfertilized than for fertilized trees. Annual primary productivity was linearly related to both radiation absorbed and to mass of N in the canopy.