Effect of Dwarfing Interstocks on Xylem Sap Composition in Apple Trees: Effect on Nitrogen, Potassium, Phosphorus, Calcium and Magnesium Content

This paper concerns nutrient concentrations in xylem sap collectedfrom above and below M.8, M.9, M.26 and M.7 dwarfing interstocks.The sap flowing from above an interstock had lower concentrationsof nutrients than that from the rootstock levels and these differencesincreased with the dwarfing effect of the interstock. There were indications that nutrient concentrations were enhancedbelow interstocks but were reduced in the sap flowing from theinterstocks into the scions. Generally these reductions weregreater the more dwarfing the effect of the interstock. Analyses of sap from above, mid-way along and below interstocksindicated that the changes in content were produced in, or closeto, the graft union between scion and interstock.