植物葉の光合成に与える粉じんの影響に関する研究
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概要
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Various types of dust are emitted artificially and naturally into the atmosphere through industrial processes, road traffic, volcanic eruptions, dust storms, etc. Around such sources a large quantity of dust cover on vegetation has been frequently observed. A highly alkaline dust like cement dust injures plant leaves visibly; even chemically inert dust affects photosynthesis and transpiration physically when it accumulates on leaf surfaces. Covering and plugging stomata, shading, increasing leaf temperature and removing cuticular wax were reported as physical effects of dust. On photosynthesis, however, almost all the previous studies only guessed the physical effects in their discussions. There are not enough related studies based on well-designed experiments. The aims of this study were to investigate the physical effects of the dust accumulating on plant leaves on photosynthesis, such as shading, plugging stomata and increasing leaf temperature, in detail, and to estimate the reduction in photosynthesis quantitatively. First, the photosynthetic rate, the transpiration rate, the stomatal conductance and the temperature of cucumber (Cucumis sativus) and kidney bean (Phaseolus vulgaris) leaves covered by chemically inert dust (Kanto loam powder and carbon black, JIS Z 8901) were measured under various conditions. Second, the similar experiments were conducted by the use of several kinds of volcanic ash from Mt. Sakurajima and Mt. Unzen-Fugendake. Last, in order to investigate the real conditions of dust, shading coefficients of the dust on the leaf surfaces of satsuma mandarin (Citrus unshiu) around the road for dump trucks and Viburnum awabuki in the urban area and suburbs in Sakai city were measured, and the reduction in photosynthesis of satsuma mandarin leaves by shading was estimated from shading coefficients and solar radiation. The results obtained in this study are summarized as follows. 1. The dust was found to decrease stomatal conductance by plugging stomata under a light condition when the stomata were open during dust exposure. The effect was larger when the dust load was larger or the particle size of the dust was smaller. However, the effect was negligible when the stomata were closed during exposure. The dust decreased the photosynthetic rate by shading the leaf surface. The dust with finer particles had a larger shading coefficient. Moreover, the additional absorption of incident short-wave radiation by the dust increased the leaf temperature, and consequently changed the photosynthetic rate in accordance with its response curve to leaf temperature. The increase in leaf temperature increased the transpiration rate. 2. The particle size distribution of volcanic ash was varied with sampling location and the date of eruption. The volcanic ash with smaller particle size and higher light reflectance had a larger shading coefficient. Since ash particles entered stomatal cavities, the stomatal conductance of cucumber leaf was decreased significantly under a light condition, even after they were washed out from the leaf surface. The temperature of the leaf covered with the ash from Mt. Sakurajima at a rate of 50gm^<-2> increased by 2.5℃ under solar radiation of 870Wm^<-2>. 3. A large quantity of dust originated from soil scattering was observed on the upper surface of satsuma mandarin leaves near the road. However, little dust was on the lower surface of the leaves, and the dust load decreased drastically with a distance from the road. While the shading coefficient of the dust on the upper surface of the leaves located in the outside of a crown changed with traffic density of dump tracks and the amount of precipitation, that in the inside little changed. The result of the estimation showed that the shading by dust decreased the net photosynthesis of satsuma mandarin leaves for each month from July to October in 1989 by 5, 9-12, 16-19 and 22-30%, respectively, when shading coefficients were 10, 20, 30 and 40%. In August 1989, the shading coefficients exceeded 30% at trees near the road. 4. The dust contaminated the leaf surfaces of Viburnum awabuki gradually in the urban area and suburbs in Sakai city. In October 1990, the mean of shading coefficients of dust on the upper and lower leaf surfaces were 4.9 and 1.6%, respectively. The coefficients around a main road doubled the mean value. In this study, it was found that dust accumulating on leaf surfaces decreases the photosynthetic rate by the following physical effects, plugging the stomata, shading and increasing the leaf temperature. The results suggest that plants around large dust sources are accompanied by the danger of a chronic decrease in photosynthesis, and consequently in growth. Examination of physical property of dust and understanding of its effect on photosynthesis enable us to estimate damage of plants. It can be said that the estimate of reduction in photosynthesis by dust from the shading coefficient are practical.
- 大阪府立大学の論文
- 1994-03-31