Physiological regulation of soybean (Glycine max L. Merr.) growth in response to drought under elevated CO2

To understand the physiological mechanism by which soybean (cultivar: Glycine max L. Merr. cv. JH13) regulates its growth in response to drought under elevated CO2 concentration, a pot experiment with two levels of CO2 (350 vs. 700 mu mol.mol(-1)) and two levels of water (well irrigated vs. drought) was conducted. Plant relative growth rate (RGR), water potential (WP), photosynthetic pigment (chlorophyll a/b, chlorophyll, and carotenoid contents), net photosynthetic rate (Pn), total soluble protein and total soluble sugar content, antioxidant enzyme activities (total superoxide dismutase, Cu-Zn superoxide dismutase, and peroxidase), and malondialdehyde (MDA) content in leaves were measured across different reproductive growth stages. The results revealed that elevated CO2 concentration increased RGR by 8.7 and 55.6% under well-irrigated and drought conditions, respectively. Elevated CO2 concentration reduced the decrease in water potential and Pn by 8.3 and 14.9% under drought condition, respectively, but chlorophyll content, chlorophyll a/b, and carotenoid content were not influenced obviously in enrich CO2 irrespective of water status. At elevated CO2, more soluble sugar and soluble protein accumulated under drought condition than under normal water condition, suggesting osmotic regulation. Antioxidant enzyme activities were slightly stimulated under elevated CO2 concentration alone, but membrane-lipid peroxidation was not alleviated significantly in the combination treatment of elevated CO2 and drought. It was possible that enzyme responses to enhanced CO2 level were found to vary with the plant species and different phenophases. These results could be used to study of crops response to future climate change, and provide some reference values for agriculture irrigation in the North China Plain.