SO2-drought interaction on crop yield, photosynthesis and symbiotic nitrogen fixation in soybean (Glycine max)

Abstract

South Africa has an energy-intensive economy, resulting in substantial SO2 pollution. Well watered and drought stressed soybean (Glycine max) were exposed to SO2 in open-top chambers to study the physiology of SO2 injury by measuring in parallel: growth, biomass accumulation, photosynthetic gas exchange, chlorophyll a fluorescence, in vitro Rubisco activity and symbiotic nitrogen fixation. A strong concentration dependent SO2-induced inhibition was displayed in all parameters. A reduction in photosynthesis occurred without any accompanying visual injury symptoms. SO2 exposure also resulted in large reductions in biomass and seed yield and root nodule ureide content. The chlorophyll a fluorescence data, pointing at impaired electron transport and formation of end electron acceptors as well as the in vitro Rubisco activity, supported the gas exchange data. Inhibition of photosynthesis, proved to be the main constraint imposed by SO2. SO2-stress was aggravated by simultaneous drought stress