Role of nitrogen accumulated in tulip roots during winter season

Abstract

Tulip plants accumulate a large quantity of N in their roots during the winter season. In order to analyze the role of root N accumulation on the growth and bulblet production, tulip plants were hydroponically cultured and a ¹⁵N feeding experiment was carried out. All the plants were fed with a ¹⁵N labeled culture solution for 1 month during winter, and two treatments were applied thereafter: one group of plants continued to grow in a standard culture solution containing N (+N treatment), and another was cultivated in N-free medium (-N treatment). At the time of planting one planting bulb on the average contained about 30 mg of stored N, and an additional amount of 20 mg labeled N was absorbed during the ¹⁵N feedings. On January 11 immediately after ¹⁵N feeding, 51% of total N was distributed in the roots, 30% in mother bulb scales, 15% in shoots, and 3% in the basal plate, respectively. At this stage, ¹⁵N labeled N was distributed as follows: roots 77%, mother bulb scales 11%, shoots 8%, and basal plate 2%. In the roots, 63% of N was derived from absorbed N and 37% originated from the planting bulb. The N absorbed during winter remained mainly in the roots. In addition, some part of N originating from the bulb was used for root growth. As a result the N content as well as concentration in the roots significantly increased during the underground life in winter.

The +N or -N treatment after ¹⁵N feeding affected appreciably the accumulation and distribution patterns of total N, the onset of senescence, and bulblet yield. Compared with the +N treatment, the plants cultured in the -N medium exhibited earlier senescence, and the yield of the daughter bulbs was lower due to the limitation of N supply after sprouting. Although the N treatment markedly affected the growth and translocation of N, the distribution pattern of ¹⁵N was basically not affected. At first 70–80% of ¹⁵N was stored in the roots until sprouting, then most of it was rapidly translocated mainly to the leaves, and finally about half of ¹⁵N was utilized for daughter bulb production in either treatment.

The fate of N in the above-ground parts was essentially similar both for the N originating from the bulb and N absorbed from the roots during winter. Either N translocated mainly to the leaves after sprouting, then finally about half of N was recovered in the daughter bulbs at harvest.

It was suggested that N absorbed and accumulated in the roots during the winter season may play an important role in supplementing the N originally stored in the mother bulb. In addition, the N accumulated in the roots was more rapidly and readily utilized for leaf development just after sprouting, compared with N originating from the mother bulb scales

Abbreviations
BN	=	N originating from mother bulb
DW	=	dry weight
FW	=	fresh weight
LN	=	labeled N
TN	=	total N

Key Words:

• ¹⁵N
• tulip
• root
• N accumulation