Paper Reviewed
Hao, X.Y., Li, P., Li, H.Y., Zong, Y.Z., Zhang, B., Zhao, J.Z. and Han, Y.H. 2017. Elevated CO2 increased photosynthesis and yield without decreasing stomatal conductance in broomcorn millet. Photosynthetica 55: 176-183.

Broomcorn millet (Panicum miliaceum L.) is one of the oldest cultivated crops in the world, first appearing in China around 7,000 years ago. As a C4 crop, it is predominately grown in the semiarid and infertile mountainous regions of northern China, central Asia and Russia given its ability to survive in water-limiting and nutrient-poor soils. In China, broomcorn millet is presently cultivated on over one million hectares, mainly by low income farmers. Yet, despite its regional importance, Hao et al. (2017) note that "the extent of any direct or indirect stimulation of photosynthesis, growth, and yield of broomcorn millet by elevated CO2" remains unknown, although such a stimulation, were it found to occur, "could have major economic and social implications in those relatively poor areas [in which it is cultivated]."

In an attempt to fill this data deficiency, Hao et al. conducted a CO2-fertilization experiment over the course of two growing seasons (2013 and 2014) in which they grew broomcorn millet in open-top chambers at Shanxi Agricultural University (Taigu, Shanxi, China) under ambient and elevated (+200 ppm) CO2 conditions, measuring a number of growth-related parameters both during and at the conclusion of the growing season. And what did their experiment reveal?

According to the seven Chinese researchers, elevated CO2 "significantly enhanced the mass of leaves, stem, panicle, and aboveground biomass per m² by 29.9, 41.6, 36.3 and 37.3% in 2013, and by 56.0, 35.9, 12.9 and 23.8% in 2014, respectively." Additionally, they determined that elevated CO2 increased the number of grains per plant and seed mass per m² increased by 31.8 and 34.2 % in 2013 and by 12.0 and 13.6% in 2014, respectively. Elevated CO2 also enhanced yields in both years by an average of 25.5%.

The above findings are significant in that they denote large CO2-induced plant growth enhancements that tend to be more widely associated with C3 plants, illustrating the fact that C4 plants can and do benefit from CO2 enrichment as well -- a fact that climate alarmists are loathe to admit. They are also significant for the economic value these yield-enhancements represent to the struggling low-income farmers who grow broomcorn millet in China and elsewhere, where the extra income (or even food) can make all the difference in being able to lift individuals out of poverty (and starvation). And to think that many governments and individuals are still hell-bent on not allowing these benefits to occur, as they continue to demonize CO2 and enact laws and regulations designed to limit its emission into the atmosphere.