Seasonal Changes in Carbohydrate and Nitrogen Content during the Growth of Japanese Iris (Iris ensata Thunb.)

Abstract

Seasonal changes in dry weight, carbohydrate and total nitrogen content in the various organs of Japanese iris ‘Chihayajo’ were investigated. Leaf growth measured as dry weight peaked in early October, thereafter it decreased to near zero in November. Rhizome dry weight reached its maximum in mid November when the leaf dry weight began to decrease. The spring leaf growth started in March, whereas the increase in root dry weight was not detected until early May. Total sugar and starch content in a plant which distributed mainly in the leaves and roots increased up to early October. Total sugar and starch in the roots decreased rapidly during the sprouting period. A rapid increase in total sugar and starch content was observed in the scape due to its growth, while no major changes were detected in other organs. Total nitrogen content in each organ increased from August to early October, thereafter itt continued in the rhizome until November with leaf senescence. The nitrogen content in the rhizome decreased with the onset of spring growth of leaf and scape. From these results it appears that in Japanese iris the carbohydrate reserves in the roots and the nitrogen compounds stored in the rhizome and roots are utilized for growth resumption.