Nitrogen Uptake and Allocation in Sweet Viburnum During a Root Growth Flush

Most woody ornamentals exhibit episodic growth flushes and nitrogen (N) uptake has also been demonstrated to be seasonal. However, there is little information on N uptake in relationship to plant growth cycle. In this study, N uptake and allocation of sweet viburnum during periods of low and high root elongation rates were studied. Plants were fertilized with ammonium nitrate (¹⁵NH₄ ¹⁵NO₃) and after 6 d N absorption was determined. Significantly more N was absorbed by plants with low root elongation rate compared with plants with high root elongation rate. About 70% of the N absorbed by plants with low root elongation rate was allocated to the mature leaves compared to 35% on plants with high root elongation rate. It was evident that root growth activity influenced N absorption and allocation. Although only a small amount of the N absorbed by plants with low root elongation rates was allocated to the immature leaves, significantly more N was allocated to the immature leaves by plants with high root elongation rates. It is possible that the N necessary to support immature leaf growth, when root elongation rate is low, is provided by mobilization from other parts, possibly mature leaves.