RT Journal Article SR Electronic T1 Changes in Leaf Thickness, Chlorophyll Content, and Gas Exchange of a Landscape Tree, Xanthostemon chrysanthus, Treated with Paclobutrazol and Potassium Nitrate JF Arboriculture & Urban Forestry (AUF) FD International Society of Arboriculture SP 53 OP 63 DO 10.48044/jauf.2021.005 VO 47 IS 2 A1 Ahmad Nazarudin Mohd Roseli A1 Tsan Fui Ying A1 Normaniza Osman YR 2021 UL http://auf.isa-arbor.com/content/47/2/53.abstract AB Paclobutrazol (PBZ)(0 g L−1, 0.125 g L−1, and 0.25 g L−1) and potassium nitrate (KNO3)(0 g tree−1, 100 g tree−1, and 200 g tree−1) were tested on a landscape tree, Xanthostemon chrysanthus (F. Muell.) Benth., in an attempt to enhance its stress tolerance under harsh urban conditions. Significant effects on tree height, diameter at breast height, canopy diameter, leaf area, and anatomy of tree leaves and stems in response to PBZ and KNO3 have been previously reported; in addition to these, the influences on leaf thickness and leaf physiology, including chlorophyll content and gas exchange, are discussed in this study. Relative chlorophyll content was significantly increased with PBZ and/or KNO3, enhancing leaf greenness. Increased leaf thickness of up to 13.37% at 6 months after treatment with a combination of PBZ and KNO3 was observed. The presence of PBZ significantly reduced the photosynthetic and transpiration rates and stomatal conductance. Reduced leaf physiological traits combined with thicker leaves would be beneficial for trees to tolerate harsh urban settings. Therefore, a combination of PBZ and KNO3 is recommended for stress tolerance enhancement of X. chrysanthus grown as a landscape tree.