Arboriculture & Urban Forestry 41(6): November 2015 339 Figure 1. Growing season maximum daily air temperature and maximum daily vapor pressure deficit at maximum daily air tempera- ture for Lubbock, Texas, U.S., during A) 2003, B) 2004, and C) 2005 growing seasons. sons one, two, and three, respectively. Additionally, mean maximum daily VPD for each growing sea- son was 3.7, 3.3, and 3.4 kPa for growing seasons one, two, and three, respectively. During growing seasons one, two, and three, maximum daily vapor pressure deficit was greater than 4.0 kPa for 38%, 31%, and 33% of growing season days, respectively. In a study investigating response of green ash, Austrian pine (Pinus nigra), and northern red oak (Quercus rubra) to urban VPD, Cregg and Dix (2001) reported summer maximum air tempera- tures in Lincoln, Nebraska, U.S., ranging from 18°C to 42°C, and VPD ranging from 6.3 to 12.1 kPa. The results of the current study are similar to a study conducted by Bush et al. (2008). They examined gas exchange and growth of a number of tree spe- cies [A. platanoides (Norway maple), G. triacanthos, Platanus acerifolia (London planetree), Populus fre- montii (Freemont cottonwood), Quercus gambelii (gambel oak), and Q. rubra] growing in urban Salt Lake City, Utah, U.S. Over the course of a single summer they reported daily maximum tempera- tures ranging from 10°C to 35°C, and vapor pressure deficits ranging from less than 1 to 5 kPa. Although not conducted in an urban setting, climatic con- ditions encountered by trees in the current study simulate conditions reported for many urban areas. Pre-dawn ψl was least negative for trees receiv- species (across all irrigation treatments), ‘Autumn Blaze’ maple trees were under less water deficit stress (more positive ψl ing the greatest amount of irrigation (Figure 2A), while trees receiving the least amount of irriga- tion had the most negative pre-dawn ψl . Between ) when compared to shan- tung maple trees (Figure 2A). More negative pre- dawn ψl reflects limited soil moisture available to deficit stress of shantung maple. However, Barton and Walsh (2000) examined ψl reduced irrigation has been reported for numerous woody landscape plants (Stabler and Martin 2000; Niu et al. 2008; Montague and Fox 2009), and sev- eral maple species in particular (Pair 1994; Zwack et al. 1998; Zwack et al. 1999; Barton and Walsh 2000; St. Hilaire and Graves 2001; Bush et al. 2008). Little information is available relating ψl the roots, or an inefficient water conducting system (Nash and Graves 1993; Zwack et al. 1998). Water deficit stress (more negative ψl ) in response to to water of transplanted (using a 1.2 m tree spade) and non-transplanted shantung maple trees. They reported pre-dawn and ©2015 International Society of Arboriculture
November 2015
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