Understanding how plants are able to change their structural, physiological, and mechanical properties in response to various propagation methods can help to improve both their performance and their survival when transferred to field conditions. To identify changes between the routinely applied vegetative propagation techniques of in vitro micropropagation and splice grafting we assessed leaf performance for any differences in midrib vascular traits, nanomechanical properties of tracheary element cell walls, and photosynthetic traits in the dutch elm hybrid cultivar Dodoens (i.e., open-pollinated Ulmus glabra ‘Exoniensis’ × Ulmus wallichiana P39). The propagation techniques appear to have had a direct effect on a large portion of the vascular traits. In the micropropagated plants, the water-conducting area within the primary xylem tissue contained a significantly greater number of tracheary elements which suggests hydraulic safety. In the grafts, the water-conducting area contained a significantly smaller number of tracheary elements, in which the lumen areas were slightly larger than those of the micropropagated plants, resulting in a significantly higher size to number ratio which may indicate a fast and more effective water transport system. Quantitative nanomechanical mapping measurements from atomic force microscopy (AFM) revealed that the tracheary elements of the micropropagated plants formed stiffer cell walls quantified by the reduced Young’s modulus of elasticity (MOE) than those of the grafts. The effect of the rootstock might contribute to the differences in vascular traits, as well as to the differences in cell wall stiffness and cell wall deformation observed between the stock types. The micropropagated plants were subjected to a more sensitive stomatal regulation of gas exchange resulting in the lower rates of net photosynthesis and transpiration. But the higher values of both instantaneous water-use efficiency (WUEinst) and chlorophyll a fluorescence yields found in the micropropagated plants indicate a higher acclimation capacity to stressful environmental conditions specifically for this stock type. Both stock types formed compact homogeneous clusters clearly separated from each other in the multivariate leaf trait analysis.
Determination of wood anatomy traits and the chemical attributes of plant cell walls is of great importance for the evaluation of both the effects of hybridization and the results of breeding strategies within the genus Ulmus, because these are both aimed at an enhanced tolerance to dutch elm disease (caused by Ophiostoma ulmi and O. novo-ulmi) and to the improvement of trees having desired mechanical properties. The objective of this study was to determine whether the routinely applied vegetative propagation techniques of in vitro micropropagation or grafting would result in any change to lignin monomer composition and content, macromolecular traits of cellulose, neutral sugar composition, or the vascular and fiber anatomy traits in the stems of the dutch elm hybrid cultivar Dodoens (i.e., open-pollinated Ulmus glabra ‘Exoniensis’ × U. wallichiana P39). Propagation techniques appeared to have no direct effect on lignin monomer composition. The differences in the relative proportion of guaiacyl units in lignin between the stock types were not significant, showing that no advantage could be attributed to either stock type toward an enhanced tolerance to dutch elm disease. The micropropagated plants reached significantly higher values for 13 traits (32.5%), primarily associated with the relative proportion of d-glucose and the macromolecular traits of cellulose to compensate for a lower content of holocellulose. The grafts reached higher values for 10 traits (25%), including the relative proportions of d-xylose, d-mannose, and d-galactose. The effect of the rootstock might contribute to different amounts of these cell wall substances in the grafts. The grafts also reached a higher lignin content, which may provide minor advantages in terms of mechanical and physical properties to the cell walls of this stock type. Similarities between the stock types were found for 17 traits (42.5%). Both stock types formed compact homogeneous clusters clearly separated from each other in the multivariate wood trait analysis.