Ecology of SO 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 SO fumigations. SO concentrations can be continuously monitored and manipulated between 0 and 2.0 ppm. Rates of total SO uptake and SO absorption through stomates of a fumigated leaf can also be determined.Using this system we compared the effects of SO 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 SO fumigation than Heteromeles arbutifolia, an evergreen shrub. The differences in photosynthetic sensitivity could be attributed, in large part, to differential SO absorption rates.