Translocation of Nitrogen in the Xylem of Field-Grown Cherry and Poplar Trees during Remobilization

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 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. 15N fertilizer was applied to the soil around ten year old Prunus avium and Populus trichocharpa var. Hastata (Dode) x Populus balsamifera var. Michauxii (Henry) Farewell trees before bud burst and used to label N taken up by the roots. Recovery of unlabelled N in xylem sap and leaves was used to demonstrate that P. avium remobilizes N in both glutamine (glu) and asparagine (asn). Sap concentration of both rose sharply after bud burst, peaking 14 days after bud burst for gln, and remaining high for some 45 days for asn. No 15N enrichment of either amide was found 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 again before the amide was enriched with 15N, 40 days after bud burst. Sampling the xylem sap of clonal P. avium trees at different positions within the crown was used to assess if the position of sampling affected the amino acid and amide composition of the sap. Sap was sampled during remobilization (when the concentration of gln was maximal), at the end of remobilisation and at the end of the experiment (68 days after bud burst). While the date of sampling had a highly significant effect upon sap composition, the effect of position of sampling was found to be marginal. The results are discussed in relation to the N translocation in adult trees and the possibility of measuring N remobilization by calculating the flux of N translocation in the xylem.

MILLARD Peter;  WENDLER Renate;  GRASSI Giacomo;  GRELET Gwen-Aelle;  TAGLIAVINI Massimo; 

2006-09-25

HERON PUBLISHING

JRC32022

https://publications.jrc.ec.europa.eu/repository/handle/JRC32022,