Ecology of SO2 resistance: III. Metabolic changes of C3 and C4 Atriplex species due to SO2 fumigations.

The photosynthetic processes of two ecologically-matched, herbaceous Atriplex species differed in their response to SO2 fumigations. Atriplex triangularis, a C3 species, was more sensitive than the C4 species, A. sabulosa. This difference in sensitivity can be attributed in part to the higher conductance of the C3 species in normal air and saturating light as well as greater stimulation of stomatal opening following exposure to SO2. In addition, photosynthetic mechanisms of the C3 species had higher intrinsic SO2 sensitivity than the C4 species. Differences between photosynthetic responses of these two species may also reflect differences in morphological configuration of mesophyll tissues and greater SO2 sensitivity of the initial photosynthetic carboxlating enzyme of the C3 species. It is likely that certain of the differences in photosynthetic SO2 sensitivity of these contrasting C3 and C4 Atriplex species are characteristic of C3 and C4 plants in general.