The effect of smoke on the photosynthetic gas exchange of Chrysanthemoides monilifera

The effect of smoke on the germination of various fynbos species has been well documented. However, little work has been done on the effect of smoke on mature plants. This study investigated the effect of smoke on the photosynthetic gas exchange of Chrysanthemoides monilifera. Potted plants given a one-minute exposure to smoke were significantly affected within half an hour. Stomatal conductance, CO2 assimilation rate and intercellular CO2 levels were significantly reduced and these reductions persisted for five hours, subsequent to which the three parameters recovered to control levels over the next 24 h. Reduction in CO2 assimilation rate was the consequence of both stomatal and mesophyll effects, the latter including decreases in both carboxylation efficiency and RuBP regeneration capacity. The factors responsible for these effects appear not to be related to the temperature or CO2 concentrations of the smoke and further investigation is required to elucidate the causal factor(s). Unlike gas exchange parameters, PSII photochemical efficiency was unaffected by the treatment. Repeated exposure to similar smoke treatments resulted in acclimation such that no significant reductions in CO2 assimilation rate or stomatal conductance were evident, after a smoke treatment. The photosynthetic gas-exchange of field grown plants, measured two weeks subsequent to the exposure to smoke from a natural fire, showed no response. A result that was anticipated from laboratory studies where recovery following single smoke exposure was shown to occur within 24 h.