Comparative studies on the distribution of foliar or root applied 15N‐nitrogen in Beta vulgaris species

Abstract

AbstractRecent anatomical studies on sugar beet suggest direct vascular connections between ontogenetically corresponding leaves and segments in the storage root (Stieber and Beringer, 1984). The objectives of two experiments were to test the use of these transport routes in the distribution of 15N.In adult Beta vulgaris L., spp. vulgaris plants (fodder beet cv Kyros and sugar beet cv Kawetina) 15NH4 15NO3 was applied to leaf 10 (young) and 21 (old) respectively. Distribution of 15N within the plant was determined 2, 7 and 21 days later.In fodder beet 15N applied to leaf 21 was exported to 63% into the storage root, to 11% into younger leaves; the corresponding percentages in sugar beet were 51% and 31% respectively. 15N applied to leaf 10 was exported to only 37% into the storage root, 7% and 15% were translocated into the older leaves of fodder and sugar beet respectively.This pattern of 15N distribution does not fully contradict with the expected use of assumed vascular routes. It is suggested that N exported from an older leaf does not exclusively migrate into the ontogenetically corresponding tissues of the storage root, but part of the N is imported by the younger leaves and from there exported into the peripheral regions of the storage root. This view is supported by a short‐term experiment on 15NO3‐ root‐uptake by six week old fodder and sugar beet plants which gave the following sequence of specific 15N labeling: lateral roots ≧ young leaves > root crown > old leaves > storage root.