Studies of canopy structure and water use of apple trees on three rootstocks

Canopy structure and water use was studied on full size, fruit bearing apple (Malus domestica, Golden delicious variety) orchards on three rootstocks: M9, MM106 and the local Hashabi. Structure was measured by the gap fraction inversion method and crop water use (sap flow) by the heat pulse technique. The results showed that leaf area index (LAI) was not significantly different for each rootstock even though measured leaf area (LA) per tree differed greatly. Results also showed LAI measured destructively differed by less than 1 from the gap fraction inversion measurements. No significant differences in LAI between the two orchards (M9, MM106) were found in either measurement method, indicating good relative accuracy of the gap fraction inversion method. Water use of the M9 orchard was much less than that of MM106 and Hashabi orchards, and measured water use was not well correlated with water application based on a graduated class A pan crop factor for the three orchards. The dwarfing rootstock, M9, had the lowest canopy conductance, and was found to have lower sunlit leaf conductance in the porometer measurements, so it is in a condition of water stress. However, the M9 orchard received enough irrigation, therefore, water stress in M9 orchard was probably not caused by insufficient irrigation, but by high resistance to water transport in the stem or root.