Leaf and Floret Production in Sunflower (Helianthus annuus L.) as Affected by Nitrogen Supply

Abstract

Both the vegetative and the floral meristems of glasshouse-grown sunflowers respond to nitrogen supply in the same way. The duration of leaf and floret production is unaffected but the rate of production is decreased by low nitrogen supply. Thus both final leaf number and floret number are lowest at the lowest nitrogen supply. The activity of the vegetative meristem is directly related to the content of reduced nitrogen of the plant. Relief of nitrogen stress in the middle of the vegetative phase allows final leaf number to reach the unstressed number. However, relief of nitrogen stress during floral initiation showed that floret number is a function of the plant's content of reduced nitrogen at the beginning of floret production. Relief of nitrogen stress from the middle to the end of floret production did not increase floret number. Nitrogen supply did not influence the duration but did affect the rate of leaf expansion. Relief of nitrogen stress after leaf and floral initiation were complete caused a larger final area in those leaves still expanding and also lessened apical dominance so that some axillary buds developed into small flowers.