Effects of sulphur dioxide on photosynthesis in the succulent Augea capensis Thunb

摘要

The impacts of sulphur dioxide (SO_2) pollution on succulents in arid environments are relatively unknown and the few studies that have considered these effects focused primarily on species exhibiting crassulacean acid metabolism (CAM). However, the unique metabolic adaptations in CAM species make it difficult to extrapolate these findings to succulents with typical C_3-mode CO_2 assimilation. We investigated the effects of SO_2 treatments (1.3 and 0.6ppm), administered under controlled growth conditions, on potted plants of Augea capensis Thunb., a succulent exhibiting C_3-mode photosynthesis. The effects on photosynthesis were assessed by means of CO_2 assimilation and chlorophyll a fluorescence measurements. Surprisingly, the only inhibitory effects on photosynthesis were induced when SO_2 fumigation occurred in the dark. An inhibition of 38% and 6_2% in carboxylation efficiencies and CO_2 saturated rates of photosynthesis were observed. However, these effects only occurred at the highest concentration and were fully reversible, indicating no permanent metabolic damage. Only minor effects on photosystem II electron transport were observed, indicating that photochemical reactions were not the primary site of inhibition. An explanation, based on possible diurnal differences in cellular capacity for SO_2 detoxification, is proposed for the observed diurnal (day versus night) differences in SO_2 sensitivity in this species.