Abstract
The single and combined effects of O3, NO2 and SO2 on net photosynthetic rate (Pn) and leaf diffusive conductance (LDC) in 3-year-old Japanese cedar clones (Cryptomeria japonica D. Don, cv. Shibahara) were investigated. Moreover, the effects of air temperature (15, 25 and 35°C) and humidity (50 and 70% RH) on the response of Pn and LDC in the clones of two cultivars (Shibahara and Nakagen) to the mixture of 0.1 ppm O3 and NO2 were also investigated. At 25°C and 70% RH, the Pn and LDC in Shibahara clones did not reduce when they were exposed to 0.1 ppm O3, NO2 and SO2 alone for three hours. However, the exposure to the mixture of the three gases resulted in the significant reductions in Pn and LDC. The reduction in Pn was caused not only by reduction in stomatal conductance but also by that in mesophyll conductance.
Although there were no effects of the mixture of 0.1 ppm O3 and NO2 on Pn, the effects on LDC depended on cultivars, air temperature and relative air humidity. By the exposure to the mixture of O3 and NO2, the LDC in Shibahara clones was significantly reduced at 15 and 35°C under the condition of 70% RH, while it was not reduced at 50% RH. On the other hand, no change in the LDC in Nakagen clones simultaneously exposed to O3 and NO2 was detected under all experimental conditions.
