Growth of and Phosphorus Partitioning in Eucalyptus pilularis Smith Seedlings Raised in a Phosphorus-Deficient Soil

Abstract

Eucalyptus pilularis Smith seedlings were raised in a glasshouse for 260 days in a phosphorus-deficient forest soil. Over this period, growth was divided into two major phases. Phase 1 was characterized by an initially high but rapidly declining relative growth rate and, at least after 26 days from sowing, a very low rate of phosphorus acquisition. Phase 2, delineated at around 116-134 days from sowing and previously correlated with the degree of ectomycorrhizal development, commenced with an abrupt increase in the rate of both parameters. Over the last 90 days of Phase 1 the roots received an increasing proportion of shoot dry matter production and accumulated 86% of current phosphorus acquisition. Continued, but slow, shoot development during this time was made possible by high re-use of phosphorus within the shoot. During Phase 2, increased transfer of phosphorus to the shoot (50% of total net uptake) reduced the dependence on remobilized phosphorus and resulted in a marked stimulation of leaf production. In addition to utilizing the limited phosphorus available for dry matter production very efficiently, it is proposed that the success of this typically fast-growing species under such a degree of phosphorus stress was aided by the finely tuned responsiveness of both phosphorus deployment and growth rate to fluctuations in the soil phosphorus supply.