Changes in Leaf Thickness, Chlorophyll Content, and Gas Exchange of a Landscape Tree, Xanthostemon chrysanthus, Treated with Paclobutrazol and Potassium Nitrate

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 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.

The effect of atmospheric deposition on potassium accumulation in several tree species as a biomonitor

“…The most well-known source of K in the soil minerals such as feldspar and mica although it is found in dust and rainfall likely comes from terrestrial sources [15]. The effects of differences in presence of K in different plants on species' anatomy, morphology, and plant metabolism couldn't be explained yet and they are still debated [16]. It was shown that the presence of K allowed the trees to overcome the stress conditions.…”