High SO2 resistance of Clethra barbinervis established in a smoke‐polluted area of Ashio, Tochigi Prefecture, Japan

Abstract

AbstractThe effect of SO2 on the photosynthesis of Clethra barbinervis collected from a smoke‐polluted area near the Ashio copper smelter in Tochigi Prefecture was compared with C. barbinervis collected from a nonpolluted district in Tsukuba, Ibaraki Prefecture and Quercus mongolica var. grosseserrata grown in a nonpolluted field in Nagano Prefecture. The plants were exposed to 0.5–1.5 p.p.m. SO2 for 90 min (short‐term) and to 0.3 p.p.m. SO2 for 31–39 days (long‐term). The Clethra plants from both sites had a lower intrinsic stomatal conductance and photosynthetic rate than Quercus plants. Short‐and long‐term fumigation caused stomatal closure in Quercus plants, but had little effect on the stomatal conductance of Clethra plants. Under short‐term fumigation, nonstomatal photosynthetic inhibition per unit of absorbed SO2 was smallest in Clethra plants from Ashio. Long‐term fumigation caused photosynthetic decline and visible foliar injury to Quercus plants, but had no effect on Clethra plants from Ashio. Consequently, Clethra plants from Ashio had a higher photosynthetic rate than Quercus plants after long‐term fumigation. These results suggest that C. barbinervis populations in the smoke‐polluted area of Ashio had evolved high SO2 resistance connected with SO2 detoxification ability in mesophyll cells.