Effects of kaolinite as a reflective antitranspirant on leaf temperature, transpiration, photosynthesis, and water‐use efficiency

Transpiration and photosynthesis are influenced by the optical properties of leaves. Application of a uniform white coating of kaolinite (about 225 mg dm −2 ) to the upper leaf surface produced significant changes in the spectral curves (reflectivity, transmissivity, and absorptivity) of Valencia orange leaves. Photosynthetic light response curves of leaves of orange, lemon, rubber plant (all hypostomatous), and bean (amphibiostomatous) were modified by the reflective material, which at low light intensities decreased photosynthetic rates and increased light saturation levels. The white coating cooled the leaves 3–4°C and reduced transpiration 22–28% under conditions of high light intensity, warm air, low relative humidity, and low wind velocity. However the rubber plant under the same conditions showed a smaller reduction in transpiration (less than 10%), indicating effective self‐regulation of its water loss. These experiments demonstrated that water‐use efficiency of leaves can be improved, particularly under high light intensities.