GROWTH ANALYSIS OF THE EFFECT OF PHOSPHORUS NUTRITION ON SEEDLINGS OF EUCALYPTUS GRANDIS

Eucalyptus grandis seedlings were grown in growth units in which plant roots were suspended in air while continuously being sprayed with nutrient solution (aeroponic system). Phosphorus was added to nutrient solutions in exponentially increasing amounts which determined plant growth. Phosphorus was added at five different relative addition rates. The proportion of dry matter in stems increased with plant size, but was independent of plant internal phosphorus concentration. In contrast, the ratio of root to leaf dry weight decreased almost 2-fold with increasing phosphorus concentration but changed little with plant size, and specific leaf area more than doubled with increasing phosphorus concentration. Carbon fixation rate per unit plant dry weight increased about 5-fold with increasing nutrient addition rate over the range of addition rates used. That increase was due to a doubling in specific leaf area and a doubling in assimilation rate per unit leaf area, while leaf weight as a fraction of total plant dry weight increased by about 20%.