Phosphorus Economy in Seedlings of Pinus Densiflora and Larix leptolepis

The seasonal changes of phosphorus content and its balance sheet in each organ of the current-year and two-year-old (till August) seedlings of an evergreen conifer, Pinus densiflora and a deciduous conifer, Larix leptolepis were studied under the field conditions of Tokyo.The phosphorus concentration on the dry weight basis was highest in the leaves of both species, and the amplitude of the seasonal variation was larger in the larch than in the red pine. The seasonal changes of dry weight and the total phosphorus contents showed characteristic patterns essentially common to the both species, except for some differences caused mainly by the defoliation in the larch.The total phosphorus content of an entire larch plant was kept almost constant in the latter half of the growing season in spite of the dry matter loss by defoli-ation. Prior to the defoliation, most of phosphorus contained in the leaves was withdrawn in both the species. At the beginning of the growing season the rapid growth of new organs should be supported by the supply of phosphorus reserved in the older organs. About a half the amount of phosphorus accumulated in the first year was translocated and utilized for the growth in the next year.