Abstract
Nitrogen uptake by greenhouse roses is out of phase with flower shoot elongation, such that N uptake is lowest when shoots are elongating rapidly and highest when flower shoots have ceased elongation. Fertilizer labeled with
15N was supplied at different stages of one flowering cycle to hydroponically grown ‘Royalty’ rose plants to study the partitioning of recently absorbed N and the dynamics of total N within the plant. After a 2 day exposure, whole plants were harvested, separated into old and new leaves, stems, and roots, then analyzed for total N and
15N enrichment. During the period of rapid shoot elongation, N uptake from the nutrient solution supplied 16–36% of flower shoot N. The remainder, representing most of the N in the growing shoots, came from N stored in other organs, particularly old stems and leaves. The increased N uptake that occurred later in the flowering cycle was sufficient to meet flower shoot N demand and to replenish the N supply in the old foliage and woody tissues. Those organs continued to accumulate N until the subsequent bud break, when it became available for the next cycle of flower shoot development.