Effect of Xylem-fed Maple Sap on Balsam Fir Needle Abscission and Water Loss in Spring and Autumn

Postharvest trees are detached from their root system, which may deprive the trees of certain yet unknown root-derived factors normally translocated through xylem (e.g. minerals, ABA, cytokinins, and retranslocated sugars). Resupplying certain root derived factors may delay needle abscission. The objective of this experiment is to take sap from a root intact tree species (i.e. maple trees) and add it to the water supplied to balsam fir branches. Further, the effect of reverse osmosis and autoclaving the maple sap will be explored. The experiment was conducted once in spring and again in autumn to examine seasonal changes in needle abscission. The only hormones found in the maple sap were ABA and its metabolites, with PA (163.0 ng·g^-1) being the primary metabolite present. Needle retention was higher in branches harvested in autumn, as long as they were with maple sap that did not undergo RO. If the maple sap had undergone RO processes, then needle retention was slightly decreased in autumn. Needle retention generally decreased as the concentration of maple sap in the supplied water increased and this trend was accelerated if the sap was subjected to RO process. Autoclaving the sap successfully delayed the length of time for water consumption to decrease, but this unexpectedly did not translate into improved needle retention. These results suggest that factors other than ABA or its precursor may be regulating needle abscission in a root detached balsam fir.