A MODEL OF NUTRIENT RESPONSE IN EUCALYPTUS-GRANDIS SEEDLINGS

Rate of growth in tree seedlings is dependent (amongst other factors) on the rate at which nutrients are absorbed by roots. Rate of nutrient addition to Eucalyptus grandis seedlings influences rate of growth through three main physiological mechanisms: the effects of plant nutrient concentration on biomass partitioning, specific leaf area, and assimilation. A simple dynamic model is presented to describe growth of E. grandis seedlings in response to different relative addition rates of nitrogen and phosphorus as reflected in plant nutrient status. The model takes account of effects of nutrient concentrations on partitioning, specific leaf area and light saturated assimilation rate. Model simulations demonstrate the influence relative nutrient addition rate has on key processes that influence relative growth rate, and that the relative importance of each of these is dependent on plant nutrient status. If plants are deficient in nitrogen, changes in growth consequent upon improved nutrient status are mediated primarily through effects on assimilate partitioning and light saturated assimilation rate. If plants have high nitrogen status, changes in growth consequent upon improved nutrient status are mediated primarily through effects on specific leaf area. If plants are deficient in phosphorus, changes in growth consequent upon improved nutrient status are mediated through effects on assimilation. If plants have high phosphorus status, changes in growth consequent upon improved nutrient status are mediated through effects on both assimilation and specific leaf area.