Arboriculture & Urban Forestry 47(2): March 2021 Arboriculture & Urban Forestry 2021. 47(2):53–63 https://doi.org/10.48044/jauf.2021.005 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & Changes in Leaf Thickness, Chlorophyll Content, and Gas Exchange of a Landscape Tree, , Treated with Paclobutrazol and Potassium Nitrate By Ahmad Nazarudin Mohd Roseli, Tsan Fui Ying, and Normaniza Osman Abstract. 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 have been previously reported; in addition to these, the influences on leaf thickness and leaf physiology, including chloro- phyll 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 phys- iological 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. Keywords. Golden Penda; Leaf Physiology; Photosynthesis; Plant Growth Regulator; Urban Tree. tested on a landscape tree, Xanthostemon chrysanthus (F. Muell.) Benth., in an attempt to enhance its stress tolerance under harsh urban condi- tions. 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 53 INTRODUCTION A triazole compound, paclobutrazol, PBZ [(2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4- triazol-1-yl) pentan-3-ol] is widely used in managing ornamental plants. It is an inhibitor of ent-kaurenoic oxidase, a key enzyme in the gibberellin (GA) bio- synthesis pathway. Application of PBZ reduces GA content in plants, reducing cell elongation and inhib- iting growth. As an anti-GA compound, PBZ has been shown to control growth of several plant species (Mohammed et al. 2016; Xia et al. 2018; Ju et al. 2019). Obvious plant responses to PBZ treatment were reduced growth of new shoots, stem diameter, and leaf area; enhanced chlorophyll content; and modi- fied flowering and phytochemical contents in plants (Ahmad Nazarudin et al. 2007; Ahmad Nazarudin 2012; García De Niz et al. 2014). PBZ increased the size of vascular bundles, chloroplasts, and epidermal, mesophyll, and bundle sheath cells in nonwoody plants (Burrows et al. 1992; Gopi et al. 2008; Gao et al. 2011). Only a few studies reported the effects of PBZ on the anatomy of woody plants, including Syzygium campanulatum (Ahmad Nazarudin et al. 2007) and Toona ciliata (Rodrigues et al. 2016). Plants treated with PBZ were also physiologically affected. In potted Syzygium myrtifolium, PBZ reduced both photosynthetic and transpiration rates, though the sto- matal conductance was not significantly affected (Ahmad Nazarudin et al. 2012). However, in T. ciliata, the gas exchange parameters remained unaffected with PBZ application (Rodrigues et al. 2016). This heterocyclic compound also increases plants’ toler- ance towards abiotic stresses—for example, drought, flooding, chilling, and salinity. Several other studies reported that PBZ was able to improve water stress tolerance in woody plants such as Phillyrea angusti- folia (Fernandez et al. 2006) and Mangifera indica (Kishor et al. 2009). ©2021 International Society of Arboriculture Xanthostemon c hr ysanthus
March 2021
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