262 Rahman et al.: Effect of Pit Design and Soil Composistion on Performance of Street Trees 0.001]. Post hoc tests showed that Fv:Fm ratio of trees grown in open and large covered pits were higher than those grown in small covered pits. Post hoc test also showed that the ratio was higher during mid to late summer compared to early summer. Soil pH, organic carbon, and total N content of topsoil used in the open pits was also higher compared to the soil used in the small and large covered pits. Average soil pH of topsoil in the open pits (7.21) was significantly higher than the small covered (6.99) and large covered (6.98) pit [F (2, 6) = 8.22; P < 0.05]. Organic carbon and total nitrogen content of top- soil used in the open pits (3.49% and 0.26%) was also signifi- cantly higher compared to the small covered pits (2.21% and 0.17%) and large covered pits (2.20% and 0.17%) [F (2, 6) = 25.709; P < 0.01; F (2, 6) = 25.709; P < 0.01, respectively]. DISCUSSIONS Figure 7. Chlorophyll fluorescence in leaves of Pyrus calleryana trees grown in the three pit types in 2011–2012 (n = 5). Total Chlorophyll Total chlorophyll content (a and b) of tree leaves showed significant differences between both planting pits and with time (Figure 8). A two-way ANOVA showed significant dif- ferences between the planting pits [F (2, 96) = 29.570; P < 0.001] and between time [F (7, 96) = 13.687; P < 0.001]; however, there was no significant interaction between the planting pits and time. Post hoc tests showed that total chlo- rophyll content of tree leaves grown in open pits was higher than both small and large covered pits and total chlorophyll content of tree leaves grown in large covered pits was higher than those grown in small covered pits. Moreover, post hoc test also showed that the total chlorophyll content of leaves of trees grown in three different types of pits were higher in mid to late summer compared to that of early summer. The study has shown that there were significant differences in the rate of growth, morphology, and cooling effectiveness of trees grown in the three different planting pits. The tree in the open pits performed best; they grew twice as fast as trees in small covered pits and 1.5 times as fast as trees in large covered pits. The difference continued to increase over the growing seasons. In terms of morphology, they also showed almost three times more crown spread increment compared to those grown in small covered pits and 1.5 times more than those in large covered pits. Canopy density varied among the months surveyed, but trees grown in open pits showed significantly higher density through- out the experiment, and the trend was even more visible toward the end of the experiment. In general, with significantly higher stomatal conductivity, trees grown in open pits provided cooling more than double the amount by those grown in small covered pits and 1.5 times more than those grown in large covered pits. It might be thought that these differences occurred because Figure 8. Total chlorophyll content (a+b) of leaves of Pyrus calleryana trees grown in the three pit types in 2011–2012 (n = 5). Foliar and Soil Nutrient Status There were differences in the nutrient status of several ele- ments between trees grown in different types of planting pits (Table 3). One-way ANOVA showed foliar N, P, K, Fe, Mn, and Zn content of trees grown in open pits were significantly higher than those grown in small and large covered pits [F (2, 27) = 11.386; P < 0.001; F (2, 27) = 6.058; P < 0.01; F (2, 27) = 4.963; P < 0.05; F (2, 27) = 8.739; P < 0.001; F (2, 27) = 3.386; P < 0.05; and F (2, 27) = 4.535; P < 0.05, respectively]. ©2013 International Society of Arboriculture the paving on the covered planting pits reduced water infil- tration into the pit, which would have caused them increased drought stress and reduced their nutrient uptake. However, both the midday and pre-dawn leaf water potential of the trees grown in the small covered pits were actually significantly less nega- tive compared to those grown in large covered and open pits, showing that these trees were less water stressed. In contrast, the concentration of most important macronutrients such as N, P, and K, and micronutrients such as Fe, Mn, and Zn in the leaves of trees grown in open pits was significantly higher than those grown in small and large covered pits. Trees in the open pits also broke bud one week earlier and had leaf fall two weeks later compared to those grown in small covered pits. This sug- gests that the poor performance of the covered trees is due not to water deficit, but due to a lack of oxygen, which would hinder deeper rooting and ultimately affect the foliar investment and leaf gas exchange. This is certainly in line with the results of other studies (Morgenroth and Buchan 2009; Morgenroth 2011; Weltecke and Gaertig 2012). Morgenroth and Buchan (2009) and Morgenroth (2011) investigated the effect of pervious and impervious pavements on soil moisture content and aeration and in turn on the root growth of Platanus orientalis seedlings over two growing seasons. They found high moisture content underneath the pavement surface, irrespective of permeability, but a lack of aeration. Subsequently, the shallow root abundance was higher underneath the pavements but only in the case of unpaved plots did the seedlings achieve deeper rooting. It seems plausible that due to the sealing or reduced soil pore volume, the soil moisture content was higher in the upper soil layers, just as researchers of the present study found that tree planting pits with higher soil strength had increased soil moisture con-
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