Uptake, distribution and redistribution of 15nitrogen by Vicia faba under field conditions

Abstract

Abstract The uptake, distribution and redistribution of 15nitrogen applied at early flowering and early pod fill to plants of Vicia faba (var. Minica) growing in a sandy field soil was studied. Plants were harvested 1 week after application and at maturity of the pods. It appeared that 15N was preferentially transported to the youngest plant parts such as the youngest leaves, stems and the pods. Of the 15N present in the plants at maturity, 70–80% was taken up during the 1st week after application of 15NO3−1. Of the 15NO3− injected into the soil, 55% was recovered in the mature plants. The distribution of 15N within the plant changed markedly during its development. When 15N was applied during flowering leaves initially received more 15N than the rest of the plant. At maturity these leaves had fallen from the plants and the seeds contained 60% of the 15N taken up by the plants. When 15N was applied at early pod fill, 20% of the absorbed 15N was found in the pods one week after application. By maturity this value had increased to 80% (seeds 76% + pod wall 4%). One week after each application about 20% of the 15N taken up by the plants was recovered from the roots. At maturity this value was reduced to only 7%. It was estimated that 83% of 15N in the seeds at maturity was redistributed from the vegetative parts present at flowering. During the period from early pod fill to maturity, 49% of the 15N was redistributed from the vegetative parts. Redistribution contributed up to 38% of total N in the seeds in the same period. Abscising leaves contained 15–27 mg N per g dry weight depending on different environmental conditions.