Arboriculture & Urban Forestry 41(3): May 2015 Arboriculture & Urban Forestry 2015. 41(3): 113–124 113 Leaf-Gas Exchange of Five Tree Species at Urban Street Sites Sten Gillner, Sandra Korn, and Andreas Roloff Abstract. For street trees, site-specific soil and microclimate conditions can restrict growth, health, and longevity for many spe- cies. Many urban sites are characterized by a high amount of impervious surface and paved areas resulting in a high rate of sur- face runoff, low infiltration into soil, and strong reradiation effects. In maintaining the ecologic and economic benefits of street trees through future decades, it is essential to establish species with a high tolerance to stressful urban environments. Researchers measured leaf-gas exchange of Acer platanoides, Acer pseudoplatanus, Platanus × hispanica, Quercus rubra, and Tilia platy- phyllos to assess stomatal conductance, transpiration, and net photosynthesis at impervious urban sites in the city of Dresden, Germany. The results show significantly higher leaf-gas exchange rates for the species Platanus × hispanica and Quercus rubra, compared to the species Acer platanoides and Acer pseudoplatanus. The significantly higher mean values of water-use efficiency of Platanus × hispanica and Quercus rubra, and in particular the values during the selected periods with a high vapor pressure deficit, indicate more economical water consumption. Key Words. Acer platanoides; Acer pseudoplatanus; Climate Change; Dresden; Germany; Leaf-Gas Exchange; Platanus × hispanica; Quercus rubra; Street Trees; Tilia platyphyllos; Urban Trees; Water-Use Efficiency. Knowledge of environmental and climatic tolerance of urban tree species oſten fades into the background, and aesthetic attributes, tree size, and crown shape play a more important role for planners and land- scape designers (Celestian and Martin 2005). But oſten neglected are the challenging environmental and climatic conditions in urban areas that restrict the growth of many species (Gillner et al. 2013), contradicting the intended appearance and ben- efits and leading to, for example, leaf discoloration, defoliation, and crown dieback (Roloff et al. 2013). Many street tree sites are characterized by site, soil, and microclimatic conditions, causing declin- ing vitality and a short life span (Sieghardt et al. 2005; Roloff 2013). In particular, the extent of pav- ing determines degree of infiltration, rate of sur- face runoff, and further water supply of street trees (Blume 2000; Bhaduri et al. 2001; Conway 2007). Growth and vitality are considerably restricted by microclimatic conditions, such as generally higher air temperatures and lower air humidity caused by reradiation effects, higher surface temperatures, and higher wind spells (tunnel effects) in streets (Arnfield 2003; Sieghardt et al. 2005; Huang et al. 2008). This urban heat island effect may be advan- tageous for plants adapted to the hot climates used in temperate and boreal urban areas (Sæbø et al. 2005; Sieghardt et al. 2005), but for most plants and trees used in Central European cities, like Dresden, Germany, these specific soil and climatic terms might induce high levels of water and heat stress. Further, in Central Europe the problem of water shortage during vegetation period will intensify due to long-term trends, with generally rising average temperatures and more frequent weather extremes, like periods of drought and heat waves (Bernhofer et al. 2009; IPCC 2013). Although projected precipita- tion amount and distribution is more uncertain than temperature projections (Bernhofer et al. 2009), even under constant precipitation, higher temperatures will increase evaporation and shorten water supply. Leaf-gas exchange measurements character- ize stomatal conductance, transpiration, and net photosynthesis under prevailing climatic condi- tions at natural sites (Zotz et al. 2005; Morecroſt et al. 2008; Stokes et al. 2010; Aasamaa and Sõber ©2015 International Society of Arboriculture
May 2015
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