Phosphorus and Carbon Economies of Ectomycorrhizal Seedlings of Eucalyptus pilularis Smith

Abstract

The distribution patterns of phosphorus and carbon in Eucalyptus pilularis Smith seedlings raised in phosphorus-deficient conditions for at least 4 months have been examined. These seedlings possessed well developed ectomycorrhizas and there was significant retention of phosphorus by the mycorrhizal roots at low levels of phosphorus supply. A high proportion of residue phosphorus (possibly polyphosphate) was found in mycorrhizal roots and also in foliage at a level of deficiency at which very little storage phosphorus would be expected to remain. There was evidence of a control mechanism, perhaps operating via this 'storage' pool, which guarded against any overstimulation of growth rate in response to periodic increases in soil phosphorus. This control acted by regulating the amount of phosphorus available for photosynthesis, especially in those leaves with the highest potential to export carbon for growth.

It is proposed that the E. pilularis seedlings combine strategies which characterize fast-growing and slow-growing species, namely a responsiveness of photosynthesis to available phosphorus in the foliage and foliar storage of phosphorus when supply persists. Such flexibility may contribute to this species being able to compete successfully in a range of habitats of varying nutritional status.