The effects of dust storm were investigated in three wild plants named Ficus nitida, Datura stramonium and Plumeria acutifolia by means of chlorophyll fluorescence measurements, as well as, net photosynthetic rate and stomatal conductance after progressive dust deposition extended for 6 days. In the two months leading up to the storm, severe drought conditions in Riyadh, plus above average maximum temperatures resulted in high potential evapo-transpiration rates, producing severe soil moisture deficits. Exposure to dust resulted in a drastic effect on some physiological parameters including the loss of chlorophyll a and b contents, inhibition of net photosynthetic rate (PN) and significant decrease of stomatal conductance (gs). Carotenoids content and carotenoids/total chlorophyll ratio of dust stressed plants were significantly increased parallel with the progressive deposition of the dust in comparison with control plants. The maximum efficiency of photosystem II photochemistry (Fv/Fm, PSII efficiency) varied among plants collected from the same site. Our results evidenced that dust deposition decreased overall plant performance through its severe effect on photosynthesis and resulted in a significant inhibition of PSII efficiency throughout this study period.
Key words: Chlorophyll fluorescence, dust storm, photosynthesis, Saudi Arabia.