Effects of black carbon and ammonium sulfate particles on plants

Abstract

Asian countries face the problem of transboundary air pollution, including that of particulate matter with a diameter smaller than 2.5 μm (PM2.5). The deposition velocities of PM2.5 particles, such as black carbon (BC) and ammonium sulfate (AMS), onto forests are substantially high. In this chapter, we summarize the dynamics of BC and AMS deposited on leaf surfaces and we introduce experimental studies of their long-term effects on four representative Japanese forest tree species. Experimental studies of the acute effects of BC on plants have revealed its physical effects - stomatal plugging, leaf shading, and increased leaf temperature. These effects were not observed in an experimental study on the long-term effects of BC on four Japanese forest tree species, possibly because of the low amount of BC deposited on the leaf surfaces. The amounts of BC deposited on leaf surfaces differed considerably between experimental and field observation studies. Longterm AMS exposure did not significantly affect the growth of the four representative Japanese forest tree species, but significantly increased and decreased the net photosynthetic rate in current-year and previous-year needles, respectively, of Cryptomeria japonica seedlings. Hygroscopic particles such as AMS deposited on the leaf surface can establish a continuous liquid water connection between the leaf interior and surface, which enables the bidirectional transport of water and solutes between them. AMS exposure significantly increased the concentrations of NH4±, free amino acids, and total soluble protein in the current-year needles of C. japonica, suggesting that AMS deposited on the needle surfaces deliquesced, was absorbed into the needles, and was metabolized.