Paper Reviewed
Dong, J., Gruda, N., Li, X., Tang, Y. and Duan, Z. 2020. Impacts of elevated CO2 on nitrogen uptake of cucumber plants and nitrogen cycling in a greenhouse soil. Applied Soil Ecology 145: 103342.

Winter vegetable production in greenhouses is a large and growing industry in China. However, low light intensity, low air temperature and other unfavorable growing conditions at this time of year limit plant growth and yield.

To combat such limitations, Dong et al. (2020) note that growers often add large amounts of fertilizer to the soil in an effort to increase nutrient availability, uptake and ultimately vegetable production. This practice, however, in the words of the five scientists "has resulted in serious greenhouse soil degradation, e.g. soil acidification and salinization, and environmental issues, e.g. pollution of underground water."

One possible method to improve winter vegetable growth in a greenhouse environment without adding high amounts of nitrogen (N) to the soil is to simply increase the air's CO2 concentration. In this regard, Dong et al. note that "elevated CO2 can enhance plant photosynthesis, nutrient uptake and thus plant productivity," and they add that from this perspective, "elevated CO2 has been anticipated to promote plant nutrient uptake and vegetable production as an alternative practice of the excessive fertilizer input [in greenhouses]." And so it was that the researchers set out to prove this very point.

To accomplish their objective they grew cucumber (Cucumis sativus, cv. Jinmei 3) plants in open-top chambers in a glasshouse in Nanjing, China, under three CO2 concentrations (400, 800 or 1200 ppm, corresponding to ambient, elevated and super-elevated CO2) and two N application rates (0.06 or 0.24 g N per kg of soil, corresponding to low or high N). Results of the study revealed that "elevated CO2 averagely increased the biomass of the entire plant, coarse roots and fine roots by 29%, 38% and 64% whilst super-elevated CO2 increased the biomass to a lesser extent by 20%, 26% and 11%, respectively." Dong et al. also report that CO2 enrichment "improved N uptake efficiency of [the] cucumber plants as indicated by [an] increase biomass and N concentration of [the] fine roots." Further, higher levels of CO2 "decrease[d] soil N loss associated with decreased nitrification and denitrification under high N application in a greenhouse soil."

Commenting on their key findings, the authors conclude "elevated CO2 is therefore evidenced as an effective practice to alternate N fertilizer input by increased plant N uptake and decreased the risk of N loss in greenhouse horticultural system." Thus, Chinese greenhouse vegetable growers can improve food yields while also reversing years of soil degradation from excessive N application by simply increasing the levels of atmospheric CO2 within their greenhouses to harness the wonderful benefits of atmospheric CO2.