Arboriculture & Urban Forestry 39(6): November 2013 fluorescence in August 2012). Three leaves from the lower mid canopy of each tree were collected and shielded from ambient light to reach a dark adapted state (30 min. adapta- tion to the dark). Fv/Fm was measured as the ratio of maxi- mal to variable fluorescence (Maxwell and Johnson 2000). Here, Fm is the maximum fluorescence and Fv was calcu- lated by subtracting the minimum fluorescence (Fo) from Fm. Fv/Fm was measured by applying a saturating flash of white light provided by a quartz halogen lamp using PAM-2000 chlorophyll fluorometer (Heinz Walz, Effletrich, Germany). Leaf Chlorophyll Analysis The chlorophylls, Chlorophyll a and Chlorophyll b are the most important pigments for the conversion of light energy to stored chemical energy. Therefore, the content of these pig- ments can directly determine photosynthetic potential and pri- mary production (Curran et al. 1990; Filella et al. 1995). Pig- ment content is closely related to plant stress and senescence (Gitelson et al. 2003). Chlorophylls were extracted from the same mature leaves collected for chlorophyll fluorescence by grinding leaf discs (2.31 cm2 ) in a mortar. Leaf discs from two leaves of each tree were extracted from the midpoint of the leaf next to the main leaf vein. Chlorophyll concentration was estimated at 663.6 and 645.6 nm wavelengths and cor- rected for light scattering at 750 nm in a spectrophotometer (USB-2000, Ocean Optics, Dunedin, U.S.) after extraction with 80% v/v aqueous acetone. Chlorophyll content values were recorded in eight terms according to Porra et al. (1989) on the same days as the chlorophyll fluorescence measurements. Foliar and Soil Nutrient Analysis As indicated in previous studies (Rahman et al. 2011; Rahman et al. in press), nutrient availability was assessed by investigating foliar levels of essential elements. Leaf samples were collected from the middle of the terminal shoot growth on August 15, 2011, and August 29, 2012. Leaves were air dried, ground with a mortar and pestle, and sieved with a 500-micron sieve. Total N was determined by dry combustion method using LECO TruSpecTM CN autoanalyzer (LECO Corporation). Determina- tion of other essential elements viz. P, K, Ca, Mg, Al, B, Co, Cu, Fe, Mn, Mo, Ni, Se, Zn, and Na was carried out following stan- dard procedure using inductively coupled plasma atomic emis- sion spectroscopy (ICP-AES). Soil analysis was carried out to determine soil pH, organic car- bon, and total N of soils used in three types of pits. Soil samples were collected from the top 15 cm of the soil, near the tree bases, from three pits of each type of pit on April 26, 2013, and air dried at room temperature. Stones, large roots, and other coarse fragments were removed using a 200 µm sieve. Soil pH was determined using a pH meter (Mettler Toledo 259 FE20). Organic carbon contents were determined using the calorimetric method according to Motsara and Roy (2008). Total N was determined by the dry combustion method us- ing LECO TruSpecTM CN autoanalyzer (LECO Corporation). Statistical Analysis Data were subjected to ANOVA and Tukey post hoc tests using SPSS V 20 software. Differences be- tween groups were considered significant at P < 0.05. RESULTS Tree Growth and Phenology Trees in the open pits grew almost twice as fast as those grown in small covered pits and 50% faster than those grown in large covered pits (Figure 2a; Figure 2b). A one-way ANOVA showed significant differences between trees grown in dif- ferent types of pits in height growth [F (2, 27) = 3.955; P < 0.05]; in DBH growth [F (2, 27) = 17.691; P < 0.001]. More- over, trees grown in open pits showed almost three times higher crown diameter increment than those grown in small covered pits (Figure 2c). Another one-way ANOVA showed significant differences between trees grown in three types of pits in crown diameter growth [F (2, 12) = 4.425; P < 0.05] and a post hoc analysis showed that trees grown in open pits grew significantly higher in terms of height, DBH, and crown diameter than those grown in small and large covered pits. Trees grown in open pits also had more layers of leaves (Figure 3) compared to those grown in small and large cov- ered pits. A two-way ANOVA showed significant differ- ences in LAI of trees grown in three different types of pits between the planting pits [F (2, 108) = 6.103; P < 0.01], be- tween the time [F (8, 108) = 53.837; P < 0.001], but no sig- nificant interaction between the planting pits and time. Post hoc tests showed that LAI of trees grown in open pits was higher compared to the trees grown in small and large cov- ered pits. Moreover, post hoc analysis also showed that LAI was higher in mid to late summer compared to early summer. Figure 2. Annual growth rate in Pyrus calleryana trees grown in the three pit types in 2010–2012 (n = 5): (a) height, (b) DBH, (c) crown diameter increment. ©2013 International Society of Arboriculture
November 2013
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