Paper Reviewed
Xie, X., Li, R., Zhang, Y., Shen, S. and Bao, Y. 2018. Effect of elevated [CO2] on assimilation, allocation of nitrogen and phosphorus by maize (Zea Mays L.). Communications in Soil Science and Plant Analysis 49: 1032-1044.

As a C4 crop, maize (Zea Mays) is often thought to be less-responsive to atmospheric CO2 enrichment than plants like wheat or rice that use the C3 photosynthetic pathway to fix carbon. However, as noted in our Plant Growth Database (as of late 2018), the results of over 50 experimental conditions evaluating the growth response of maize to a 300 ppm enrichment of atmospheric CO2 reveal a CO2-induced stimulation of 27 percent, which value is approximately double that anticipated for C4 crops in general.

The latest scientific study to demonstrate a high growth response of maize to atmospheric CO2 enrichment comes from Xie et al. (2018). Working at the Agro-meteorological Experimental Station of Nanjing University of Information Science and Technology in Jiangsu Province, China, the five Chinese scientists grew maize (cv. Zhengdan 958) in open-top chambers for two growing seasons under ambient (~400 ppm) and elevated (approximately 550 and 750 ppm during daylight hours only) atmospheric CO2 concentrations. Their objective was to determine the impacts of elevated CO2 on maize grain yields and yield components.

Results of their study revealed that elevated CO2 increased the aboveground biomass in the 550 and 750 ppm treatments by 5 and 12 percent, respectively, whereas it increased the grain yield by a much larger 21 and 29 percent, again respectively. Additionally, elevated CO2 increased spike number, kernels per spike and 100-grain weight. Total nitrogen accumulation within the maize grains at harvest were also enhanced by CO2 enrichment, by 7 percent in the 500 ppm CO2 treatment and 70 percent in the 750 ppm CO2 treatment, helped in part by CO2-induced improvements in nitrogen translocation efficiencies.

In light of the above findings, it would appear that maize is carbon-limited at the present-day atmospheric CO2 concentration and that it will experience larger than anticipated grain enhancements similar to those observed for C3 crops as the air's CO2 concentration continues to rise in the future.