© 2006 Heron Publishing—Victoria, Canada
Translocation of nitrogen in the xylem of field-grown cherry and poplar trees during remobilization
Peter Millard (1, 2), Renate Wendler (1), Giacomo Grassi (3, 4), Gwen-Aelle Grelet (1) and Massimo Tagliavini (3)
1. Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, U.K. / 2. Corresponding author (p.millard@macaulay.ac.uk) / 3. Dipartimento di Colture Arboree, Università di Bologna, Via Fanin 46, 40127 Bologna, Italy / 4. European Commission - JRC, Institute for Environment and Sustainability, 21020 Ispra (VA), Italy / Received May 31, 2005; accepted August 13, 2005; published online January 15, 2006
Summary
Studies of small trees growing in pots have established that individual amino acids or amides are translocated in the xylem
sap of a range of tree species following bud burst, as a consequence of nitrogen (N) remobilization from storage. This paper
reports the first study of N translocation in the xylem of large, deciduous, field-grown trees during N remobilization in
the spring. We applied 15N fertilizer to the soil around 10-year-old Prunus avium L. and Populus trichocharpa Torr. & Gray ex Hook var. Hastata (Dode) A. Henry × Populus balsamifera L. var. Michauxii (Dode) Farwell trees before bud burst to label N taken up by the roots. Recovery of unlabeled N in xylem sap and leaves was
used to demonstrate that P. avium remobilizes N in both glutamine (Gln) and asparagine (Asn). Sap concentrations of both amides rose sharply after bud burst,
peaking 14 days after bud burst for Gln, and remaining high some 45 days for Asn. There was no 15N enrichment of either amide until 21 days after bud burst. In the Populus trees, nearly all the N was translocated in the sap as Gln, the concentration of which peaked and then declined before the
amide was enriched with 15N, 40 days after bud burst. Xylem sap of clonal P. avium trees was sampled at different positions in the crown to assess if the amino acid and amide composition of the sap varied
within the crown. Sap was sampled during remobilization (when the concentration of Gln was maximal), at the end of remobilization
and at the end of the experiment (68 days after bud burst). Although the date of sampling had a highly significant effect
on sap composition, the effect of position of sampling was marginal. The results are discussed in relation to N translocation
in adult trees and the possibility of measuring N remobilization by calculating the flux of N translocation in the xylem.
Keywords:
amides, amino acids, internal cycling of N, 15N labeling, Populus, Prunus, xylem sap.
