Arboriculture & Urban Forestry 47(2): March 2021 MATERIALS AND METHODS Study Site and Plant Materials A total of 81 existing X. chrysanthus trees grown at Metropolitan Batu Park, Kuala Lumpur (3°12’49”N, 101°40’43”E) were selected randomly for this study (Figure 1). The trees were planted and maintained by the Kuala Lumpur City Hall (KLCH). For the pur- poses of the experiment, all trees were selected based on their good growth performance in terms of leaf area index and for being free from pests and diseases. These trees had leaf area index values ranging from 2 to 2.41, heights from 6.01 to 6.91 m, and trunk diameters from 11.02 to 13.70 cm. The trees were planted 1 to 1.5 m away from the road shoulder and 10 m from one another. Nine treatment combinations of PBZ and KNO3 0.125 g L-1 0.125 g L-1 0.25 g L-1 (control, 100 g KNO3 PBZ, 0.125 g L-1 , 200 g KNO3 PBZ + 200 g KNO3, 0.25 g L-1 PBZ + 100 g KNO3, and 0.25 g L-1 , containing 250 g a.i. PBZ L-1 PBZ + 100 g KNO3 PBZ, , , PBZ + 200 g KNO3) with nine replications were laid out in a completely randomized design. No PBZ or KNO3 was applied to the control trees. Cultar® K Plus (13.7:0:46.3) as the source of KNO3 , and Krista™ were was applied at 3-month intervals. The first application of KNO3 was done concurrently with PBZ treatment. KNO3 was applied directly into the used in this study. PBZ was diluted with water prior to application into soil around the root collar of the trees. Each tree received 1 L of PBZ dilution, while the control tree received 1 L of tap water. PBZ was applied once at the beginning of the study (March 2012). On the other hand, each dosage of granular KNO3 soil because the KLCH did not allow foliar spraying for trees grown in the park. Thus, pocket application of KNO3 to avoid surface runoff during rainy days. Each dosage of KNO3 55 using a portable chlorophyll meter (SPAD-502, Minolta, Japan). The first fully expanded leaves from 3 branches of each tree were selected randomly for the measurement. Relative chlorophyll content was recorded monthly from April 2012 to March 2013 after PBZ and initial KNO3 treatment. A total of 27 leaves per treatment were measured in monthly sampling. Determination of Leaf Thickness Increase Changes in leaf thickness (mm) of X. chrysanthus were assessed before treatment (March 2012) and at 6 months after treatment with PBZ and KNO3 (Sep- tember 2012). The first fully expanded leaves from 5 randomly selected vegetative branches of each tree were collected for the assessment. Leaf specimens were prepared and observed under a scanning electron microscope (JEOL JSM-5610LV) as described in Ahmad Nazarudin et al. (2015). The thickness increase (%) of the palisade, spongy parenchyma, and leaf was then determined. A total of 45 leaves per treatment were sampled for the assessment. Measurement of Leaf Gas Exchange The youngest fully expanded leaves from 3 vegetative branches were selected randomly from each tree for measurement of leaf gas exchange. The measurement was conducted using a portable infrared gas exchange analyzer (Li-6400XT, LICOR, Nebraska, USA). Measurements of photosynthetic rate (mmol m-2 transpiration rate (mmol m-2 ance (mol m-2 s-1 s-1 s-1 ), ), and stomatal conduct- and 11:00 a.m. when photosynthetically active radia- tion was in the range of 500 to 1200 μmol m-2 ) were performed between 9:00 a.m. s-1 and was carried out under the tree-canopy drip line was equally divided into 4 portions, each of which was placed approximately equidistant from the others around the canopy drip line. The study was carried out for a year, from March 2012 to March 2013. During the study period, total precipitation received was 3,181.7 mm while the average temperature was between 22.9 and 33.3 °C with relative humidity of 76.4%. Measurement of Leaf Relative Chlorophyll Content For the relative chlorophyll content (leaf greenness) investigation, in situ measurement was performed by carbon dioxide concentration was at 360 to 400 ppm. The measurement was made at ambient humidity and at a maintained temperature of 28 °C. A total of 27 leaves per treatment were measured in each observa- tion. The first and second observations were made in September 2012 and March 2013, respectively. Statistical Analysis All data were subjected to 2-way analysis of variance (ANOVA) using Statistical Analysis System version 8.1 (SAS Institute Inc., Cary, NC, USA). Differences between treatment means were compared by using Duncan’s multiple range test (DMRT) at 5% level of probability. ©2021 International Society of Arboriculture
March 2021
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