Savi Tadeja, Bertuzzi Stefano, Branca Salvatore, Tretiach Mauro, Nardini Andrea
Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, Trieste, 34127, Italy.
New Phytol. 2015 Feb;205(3):1106-1116. doi: 10.1111/nph.13112. Epub 2014 Oct 29.
Urban trees help towns to cope with climate warming by cooling both air and surfaces. The challenges imposed by the urban environment, with special reference to low water availability due to the presence of extensive pavements, result in high rates of mortality of street trees, that can be increased by climatic extremes. We investigated the water relations and xylem hydraulic safety/efficiency of Quercus ilex trees growing at urban sites with different percentages of surrounding impervious pavements. Seasonal changes of plant water potential and gas exchange, vulnerability to cavitation and embolism level, and morpho-anatomical traits were measured. We found patterns of increasing water stress and vulnerability to drought at increasing percentages of impervious pavement cover, with a consequent reduction in gas exchange rates, decreased safety margins toward embolism development, and increased vulnerability to cavitation, suggesting the occurrence of stress-induced hydraulic deterioration. The amount of impermeable surface and chronic exposure to water stress influence the site-specific risk of drought-induced dieback of urban trees under extreme drought. Besides providing directions for management of green spaces in towns, our data suggest that xylem hydraulics is key to a full understanding of the responses of urban trees to global change.
城市树木通过冷却空气和地表来帮助城镇应对气候变暖。城市环境带来的挑战，特别是由于大面积铺设路面导致水资源匮乏，致使街道树木死亡率很高，而极端气候会进一步加剧这种情况。我们研究了在不同比例的周边不透水路面的城市环境中生长的冬青栎树的水分关系以及木质部水力安全性/效率。测量了植物水势和气体交换的季节性变化、对空穴化和栓塞水平的脆弱性以及形态解剖特征。我们发现，随着不透水路面覆盖率的增加，水分胁迫和干旱脆弱性呈上升趋势，进而导致气体交换率降低、栓塞发展的安全边际减小以及空穴化脆弱性增加，这表明存在胁迫诱导的水力退化现象。不透水表面的面积以及长期暴露于水分胁迫之下，会影响极端干旱情况下城市树木因干旱导致死亡的特定地点风险。除了为城镇绿地管理提供指导外，我们的数据表明木质部水力学是全面理解城市树木对全球变化响应的关键。
