Morfo-anatomske karakteristike potomstava gorskog javora (Acer pseudoplatanus L.) izloženog rastućim koncentracijama soli natrijum hlorida | Morpho-anatomical characteristics of Sycamore maple (Acer pseudoplatanus L.) exposed to increasing sodium chloride concentrations

Sycamore maple (Acer pseudoplatanus L.) and its red leaf cultivar (A. pseudoplatanus “Atropurpureum” Späth.) are widespread in urban forestry. Rapid expansion of cities as a consequence of urbanization has resulted in intensive climate changes, as well as in emergence of stress factors, such as soil salinity and drought, that exert negative effects on the overall tree performance. This dissertation provides in situ analysis of sycamore maple specimens from the Novi Sad urban area and ex situ analysis of their half-sib lines. The aim of this work was to provide: (1) analysis and characterization of urban population via phenological observations, tree biometry measurements, leaf, flower and fruit morphometric measurements, and stomata measurements; (2) selection of trees highly tolerant to soil salinity; and (3) analysis of seedlings from half-sib lines in terms of their morphological and anatomical sensitivity to high soil salinity and its half-sib variability. In situ research revealed high inter-population variability in the analyzed urban population, as well as high sensitivity of the analyzed parameters to urban environment. Provided analyses demonstrated that specific urban area factors exert strong influence on tree vitality and dimensions and proportions (allometry). Moreover, tree position in urban canyons, i.e. distance from roads and surrounding pavement areas, was shown to affect tree performance. Morphometric assessment of leaves, flowers and fruits indicated that parameters that define their proportions are less sensitive to the environmental factors compared to the measured parameters of tree dimensions. Study findings further revealed significant impact of urban area, as well as taxon differentiations, on the morphometric characteristics of the aforementioned plant organs. In addition, leaf position in the tree canopy and tree location have the greatest impact on stomatal density and dimensions, in contrast to taxa, among which no statistically significant differences were observed. Phenology of leafing and flowering is more sensitive to the surrounding factors than that pertaining to leaf- and fruit-fallout. Ex situ research, which included salt tolerance assessment of selected sycamore maple half-sib lines, showed a high level of sensitivity of morphological and anatomical parameters to soil salinity. In total, 7/25 mother trees in which half-sib seedlings were highly tolerant to salinity were selected. Under high soil salinity conditions, the following phenomena were observed: (1) reduced seedling height and steam radial increment, as well as decreasing leaf number and size; (2) declining stomatal density and size; and (3) changes in depth and proportion of trunk and root wood tissue. The most intensive changes were observed in height increment, i.e. seedlings treated with 150 mM NaCl were shorter by ~12 cm, and had ~0.4 cm smaller trunk diameter, as well as 50% fewer leaves, on average, which were significantly smaller compared to the control seedlings. Significant changes were noted in histological characteristics as well, since salinity markedly affected stomatal size and density. Leaves of seedlings treated with 150 mM NaCl had smaller and less densely packed (~70 per mm2) stomata compared to the control seedlings. Seedling steam and root wood tissue characteristics were the least affected by soil salinity. Comparative analysis of the half-sib lines revealed differences in salt sensitivity among seedlings. This phenomenon is a valuable basis for further work on the selection of sycamore maple specimens for urban environments. The present study indicates that the analyzed morphological and anatomical parameters are reliable indicators of tree adaptation to stress conditions caused by high NaCl concentration in soil. Sycamore maple and its red leaf cultivar can be appropriate taxa for use in highly urbanized areas with valuable potential for further selection work in order to improve its tolerance to adverse urban conditions.