Growth adaptation of leaves and internodes of poplar to irradiance,day length and temperature

The adaptation of absolute growth rate of leaves and internodes of Populus euramericana (Dode) Guinier cv. 'Robusta' to irradiance and day length proceeds by increases in the volume of the apex. Diameter and height of the apex increase linearly with time, resulting in linear increases in rates of leaf initiation and stem height growth that can be described by an acceleration factor. The acceleration factor is proportional to day length. The relationship between the acceleration factor and irradiance is curvilinear and saturates at irradiances above about 300 W m(-2). Absolute stem height growth rate is the product of mean relative growth rate in stem height and the length of the growing part of the stem. The temperature-dependent growth pattern of each individual leaf or internode reflects a specific relationship between its relative growth rate and organ age that is independent of irradiance and plant age; however, it is dependent on day length during the primordial phase. The constancy of the growth patterns and the correlation between leaf length and leaf initiation rate indicate that growth of primordia is predetermined in the apex, presumably by the precisely structured vascular system.