NITROGEN PARTITIONING IN ROSE PLANTS OVER A FLOWERING CYCLE

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 N-15 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 N-15 enrichment. During the period of rapid shoot elongation, N uptake from the nutrient solution supplied 16-36% of newer 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.