Ecology of SO2 resistance: I. Effects of fumigations on gas exchange of deciduous and evergreen shrubs.

A unique gas exchange system is described in which photosynthesis, transpiration, and stomatal conductance can be measured on leaves during SO2 fumigations. SO2 concentrations can be continuously monitored and manipulated between 0 and 2.0 ppm. Rates of total SO2 uptake and SO2 absorption through stomates of a fumigated leaf can also be determined.Using this system we compared the effects of SO2 on the gas exchange rates of two shrub species that co-occur in the Califormian chaparral. Diplacus aurantiacus, a deciduous shrub, was more sensitive to SO2 fumigation than Heteromeles arbutifolia, an evergreen shrub. The differences in photosynthetic sensitivity could be attributed, in large part, to differential SO2 absorption rates.