Screening for drought resistance among ornamental maples (Acer sp.). A field experiment in juvenile plants

Urban greenery is often affected by adverse environment (including inadequate water availabil-ity) of human agglomerations. Besides high aesthetic value, maples (Acer sp.) with elevated resistance to air/soil pollution, have become common components of ornamental plantations in Europe. Because of high theoretical (representativeness for species evaluation) and practical (planting age) relevancy, morphological and metabolic reactions of juvenile plants of eight maple species to one month long summer drought were studied in the experimental field to estimate the species drought resistance. In spite of marked growth differences, none from tested species showed a significant decrease in leaf relative water content indicating stress. However, in some of them activation of protective mechanisms was observed, what points to the past stress sensing. A. negundo with A. tataricum bet on transpiration area reduction (leaf shedding) and A. buergerianum, A. palmatum and A. saccharinum on osmotic adjustment (increased free proline concentration). Increase in stomatal index and/or reduction in specific leaf area, observed almost exclusively in species with continuous growth, had limited effect on the plant hydration status. Relative trunk growth was par-ticularly affected in the fast growing species. Taking into account the decisive protective mechanisms onset and trunk growth stability, species can be ordered in respect of drought resistance as follows: A. campestre, A. monspessulanum, A. platanoides, A. tataricum, A. negundo, A. saccharinum, A. palmatum and A. buergerianum.