Abstract
The physical effects of dust on gaseous exchange through stomata were investigated by measuring stomatal conductance of dusted and clean leaves. The effects of dust by increasing leaf temperature on net photosynthetic rate and transpiration rate were investigated.
Four classes of dust (JIS Z 8901: three classes of Kanto-loam powder and carbon-black), which were different in particle size and were chemically inert to plants, were made to adhere to upper surface of leaves of cucumber plants. In order to except the shading effect of dust, stomatal conductance, net photosynthetic rate and transpiration rate were measured under the condition of fairly high light intensity.
The stomatal conductance of upper surface of dusted leaves whose stomata had been open in exposure of dust to leaves decreased in light peoriod and increased in dark peoriod. As particle size of dust became smaller, the changes of stomatal conductance increased both in light peoriod and dark peoriod. There was no change of stomatal conductance of leaves which had been exposed to dust when stomata had been closed. It seemed that dust caused these changes of stomatal conductance by covering and plugging stomata.
Temperature of leaves covered with carbon-black were higher than clean leaves by 1.7-3.7°C in 15-40°C of air temperature. The net photosynthetic rates of leaves which had been exposed to carbon-black when stomata had been closed were higher than the rates of clean leaves below 25°C of air temperature, and were lower above 30°C. The transpiration rates of the same dusted leaves were higher than the rates of clean leaves by 0.4-0.6g·dm-2·hr-1 in 15-40°C of air temperature.
The results suggest that dust affects net photosynthetic rate by covering and plugging stomata, and by increasing leaf temperature.
