19. Effects of Aerosol Particles on Plants

Because aerosol particles in the atmosphere scatter and absorb incoming solar radiation, they can indirectly affect plant productivity by reducing incoming solar radiation. Conversely, aerosol particles affect plants after deposition from the atmosphere. In this chapter, we introduce both the possible indirect effects of aerosol particles on plant productivity, via reducing incoming solar radiation, and the direct effects of particulate matter deposited on the leaf surface. A wide range of experimental studies has shown the physical effects of particulate matter deposited on the leaf surface – leaf shading, increased leaf temperature, stomatal plugging, and interference with stomatal closure – that can occur in the field in Asia. Leaf shading by particulate matter reduces the net photosynthetic rate under low light conditions. The increase in leaf temperature caused by particulate matter increases or decreases the net photosynthetic rate under air temperatures below or above the optimum for photosynthesis, respectively. The light extinction coefficient of particulate matter is an important factor in the increase in leaf temperature. Stomatal plugging decreases gas diffusivity during the light period, and this can reduce the net photosynthetic rate. Interference with stomatal closure induces unexpected water loss at night, which can reduce drought tolerance. Although the chemical effects of dust depend on its chemical properties (e.g., pH), the effect of dust-induced injury cannot be explained by the effect of a single major dust component only, suggesting that dust components have an interactive effect. Currently, however, little information is available on the combined effects of the components of particulate matter.