Role of nitrogen accumulated in tulip roots during winter season

Abstract

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