Impact of Dust Deposition on Photosynthesis, Gas Exchange, and Yield of Date Palm (Phoenix dactylifera L.) cv. `Sayer’

This experiment was conducted to determine the effects of dust, rain, and pollination on photosynthesis activity and crop yield of commercial date palm (Phoenix dactylifera L.) cultivar `Sayer’. Mature trees were used for dust treatments application and assessments under Ahvaz, Iran, during the 2016-2017 growing seasons. The dust blew on the trees canopy using a blower and the leaf gas exchange was evaluated using an infrared gas analyzer on the intact leaves. After treatments, photosynthesis rate, transpiration rate, and stomatal conductance were measured. The leaf gas exchange results showed significant differences between the applied combined treatments on photosynthesis rate (from 9.18 to 0.64 μmol CO_2 m⁻²s⁻¹), stomatal conductance (from 39.9 to 6.67 mmol m⁻²s⁻¹), and transpiration rate (from 2.78 to 1.49 mmol H_2O m⁻²s⁻¹). Deposition manner of dust particles, the number of stomata in the abaxial and adaxial surfaces of leaflets, and the minimum dust- carrying capacity (MDCC) were determined using scanning electron microscopy (SEM). Stomata study using SEM showed that date palm leaflet surfaces are almost wavy and the stomata are situated in the concave surfaces in a linear arrangement on both abaxial and adaxial leaf surfaces. Although, there were no significant differences in stomatal density at the abaxial (299 mm^-2) and adaxial (300 mm^-2) leaf surfaces, the leaflet position within the leaf showed a significant influence on MDCC. The base positioned leaflets in the leaf showed the highest (2.5 mg cm^-2) and the upper positioned top leaflets showed the lowest MDCC (1.7 mg cm^-2), respectively. Also, SEM showed a sign of covering or entering dust particles into the stomata with possible stomata clog and blockage lead to the significant reduction of photosynthesis and crop yield. Besides, pollinated trees showed the maximum crop yield (59.17 Kg tree^-1), so the minimum yield was recorded on un- pollinated palm trees (1.90 Kg tree^-1).