Diurnal Variations in Non-Structural Carbohydrates, Leaf Extension, and Leaf Cavity Carbon Dioxide Concentrations inAllium cepaL.

Abstract

Diurnal changes in non-structural carbohydrates, leaf extension, and leaf cavity CO₂ concentrations were determined. Before the start of the photoperiod total non-structural carbohydrate begins to accumulate due to an accumulation of glucose and fructose. After the start of the photoperiod total carbohydrate continues to accumulate but at this time this is due to increasing sucrose levels. The pre- and early-photoperiod accumulation is finite, and a reduction of accumulated carbohydrate occurs before a more sustained increase commences. Utilization of accumulated carbohydrate commences at least 3 h before the end of the photoperiod. Leaf extension is constant throughout the dark and photoperiod. The CO₂ concentration within the leaf cavity is high at 0·3%, but declines before the start of the photoperiod and immediately after ‘lights-on’ to about 0·06%, this concentration being maintained throughout the day. A slow accumulation of internal CO₂ occurs after the end of the photoperiod.