Paper Reviewed
Wang, A., Lam, S.K., Hao, X., Li, F.Y., Zong, Y., Wang, H. and Li, P. 2018. Elevated CO2 reduces the adverse effects of drought stress on a high-yielding soybean (Glycine max (L.) Merr.) cultivar by increasing water use efficiency. Plant Physiology and Biochemistry 132: 660-665.

Many researchers have examined the interactive effects of atmospheric CO2 enrichment and drought, hoping to gather insight as to how rising levels of CO2 may impact this debilitating stress that can devastate crop yields.

Wang et al. (2018) conducted just such an analysis on soybean (Glycine max, cv. Zhonghuang 35) over the course of two growing seasons (2013 and 2014). The plants were grown in pots in open-top chambers at Shanxi Agricultural University, Taigu, Shanxi, China. The two CO2 concentrations utilized in the study were 400 ppm (ambient) and 600 ppm (enriched). Initially, all crops received adequate water, with the soil water content maintained at 60-80% of relative water content. Then, 25 days after sowing (the branching stage), Wang et al. subjected half of the plants to water stress (soil water content maintained at 35-45% of relative water content) through the end of the experiment at harvest. Various measurements were conducted throughout the experiment to evaluate plant growth and development with and without water stress as a function of atmospheric CO2.

In discussing their findings, the authors report that elevated CO2 increased net photosynthesis, water use efficiency, the effective quantum yield of PSII photochemistry, soluble sugar content, aboveground biomass and seed yield. Water stress, on the other hand, tended to reduce these parameters, with the exception of water use efficiency, which was increased under drought conditions. And when combined, elevated CO2 "enhanced the resistance to drought by improving the capacity of photosynthesis and water use efficiency in soybean leaves," which benefits further "alleviated drought-induced negative effects on aboveground biomass and grain yield of this soybean cultivar." More specifically, based on data presented in the authors' Table 1, it can be calculated that elevated CO2 increased the water use efficiency of soybean by approximately 50% and 150% under well-watered and water-stressed conditions (averaged across both years). And, based on data presented in the authors' Table 5, it can be determined that elevated CO2 stimulated both the aboveground biomass and yield of soybean by approximately 15% and 50% under well-watered and water-stressed conditions.

Consequently, in light of the above findings Wang et al. conclude that future elevated CO2 concentrations "would benefit soybean production in the arid regions of northern China" and elsewhere where drought is a limiting factor to soybean production and yield.