Arboriculture & Urban Forestry 41(3): May 2015 below -700 h. Only for the site of Tilia platyphyl- los the soil moisture regime was generally drier, resulting in lower leaf-gas exchange at dry sites. 25 Vol-%, Ψsoil Species Specific Leaf-Gas Exchange Deciduous tree species originating from temperate forests show a low level of stomatal conductance, transpiration, and high leaf surface temperatures at highly paved sites (Kjelgren and Montague 1998). Isolated trees over asphalt intercept more longwave radiation due to higher surface tem- peratures, resulting in higher water loss on warm summer days and an early closure of stomata (Kjel- gren and Montague 1998, Mueller and Day 2005), in particular of Acer platanoides (Kjelgren and Montague 1998). Forrai et al. (2012) reported just as low values of photosynthesis rates (3.68–13.03 μmol m-2 s-1 ration rates (0.85–2.65 mmol m-2 ) and correspondingly limited transpi- s-1 ) for ten dif- ferent urban tree species, like Acer pseudoplata- nus, Acer platanoides, Tilia cordata, and others. Measurements in sun canopy leaves of adult street trees revealed significant differences in leaf- gas exchange and wue among the species calculated for the total of measurements. In both years 2009 and 2010, Amax rates of Platanus × hispanica and platanus. Tilia platyphyllos reached approximately 70% of the Amax Quercus rubra reached at least the double of mean Amax Despite having a higher water use indicated by the higher transpiration rates, results for Platanus × hispanica and Quercus rubra indicate signifi- cant higher mean water-use efficiency. Therefore, these two species may be better adapted, and the species with lower water-use efficiencies may be lower adapted under the prevailing environmen- tal and climatic conditions at the urban sites. Even under irrigation, down regulation of stoma- tal conductance leads to decreased transpiration, net photosynthesis, as well as stem sap flow for Acer platanoides in periods with heat and drought (Bush et al. 2008). Although not on a significant level, plot plants of Acer platanoides restricted gs under reduced irrigation (Fini et al. 2008). Here, lowest values of gas exchange were measured for Acer platanoides, but with no further reduction in the selected periods. Reasons for this may include , Amax , and E rates of Acer platanoides and Acer pseudo- of rate of Platanus × hispanica. in the soil depth 80 cm was never 121 restricted irrigation (Fini et al. 2008). In general, though, Acer pseudoplatanus is generally ranked to be drought sensitive (Morecroſt et al. 2008; Köcher et al. 2009; Hemery et al. 2010; Scherrer et al. 2011). Tilia platyphyllos is ranked less drought sensitive than Acer platanoides (Fini et al. 2009), which is con- sistent with current findings of higher wue and gas exchange in Tilia under dryer soil. Adult forest trees of Tilia platyphyllos, however, have been reported to decrease stomatal conductance five-fold during drought, indicating Tilia platyphyllos’ drought sen- sitivity (Leuzinger et al. 2005). This study has also shown decreasing stomatal conductance with increas- ing VPD, indicating a sensitive reaction of Tilia. By contrast, Platanus × hispanica, among eight species in Warsaw, Poland, was reported to be the most tolerant of stressful urban conditions (Swoc- zyna et al. 2010), able to maintain greater con- ductance and wue than other species (Chunxia et al. 2008). Similarly, Leuzinger et al. (2010) found almost twice the stomatal conductance of Tilia platyphyllos and Acer platanoides under balanced water supply. The current study is consistent with these results, since leaf-gas exchange and wue for ©2015 International Society of Arboriculture sufficient soil water supply even during periods with lower soil moisture (at this site constantly over 25 Vol.-% in 60 cm soil depth) and ostensi- bly inherent low gas-exchange rates that resulted in no further reduction. However, physiological behavior of Acer platanoides depends on cultivar and degree of water stress (Fini et al. 2009), par- ticularly at paved urban sites (Kjelgren and Mon- tague 1998). Mean values of wue here were quite similar to that of the cultivar ‘Summershade’, with a higher susceptibility for drought stress compared to the cultivars ‘Deborah’ and ‘Emerald Queen’ (Fini et al. 2009). Physiological traits of Acer plat- anoides (Aasamaa and Sõber 2011a; Aasamaa and Sõber 2011b) and of Acer pseudoplatanus (Köcher et al. 2009) show sensitive stomatal regulation. A strong relationship of stomatal conductance and VPD was confirmed in the current study for Acer platanoides only (R² = 0.51), whereas relationship for Acer pseudoplatanus is weak (R² = 0.21). A high level of soil water supply is essential for optimal leaf-gas exchange for Acer pseudoplatanus (Köcher et al. 2009; Scherrer et al. 2011). However, some- what contradictory results from Fini et al. (2008) found values of Amax up to 4.93 μmol m-2 s-1 under
May 2015
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
