Paper Reviewed
Dabu, X., Li, S., Cai, Z., Ge, T. and Hai, M. 2019. The effect of potassium on photosynthetic acclimation in cucumber during CO2 enrichment. Photosynthetica 57: 640-645.

There is much information that remains to be gathered with respect to the combined impact of elevated CO2 and other growth-influencing variables in order to understand how plant growth will change in the future. And so in the present study, Dabu et al. (2019) studied the combined effects of elevated CO2 and potassium on the growth of cucumber (Cucumis sativus cv. Zhongnong 20).

Their work was conducted in open-top chambers within a controlled-environment greenhouse at Yunnan Agriculture University in China. Approximately two-month-old cucumber seedlings were grown hydroponically in the chambers for 43 days under either ambient (380 ppm) or elevated (1000 ppm) CO2 conditions, with the elevated CO2 only being applied in the morning from 8 am to 12 pm. Additionally, within each CO2 treatment half the plants received a potassium concentration of 120 mg L^-1 (K120) and half a concentration of 240 mg L^-1 (K240).

The results of the experiment showed that elevated CO2 increased the total biomass of the cucumbers by 73% and 33% in the K120 and K240 potassium treatments, respectively (see Figure 1). Higher potassium concentrations also positively impacted biomass, helping to increase the transport of photosynthetic products from the leaves into other plant organs (e.g., stems, roots).

Such findings above are good news for the vegetable greenhouse industry, demonstrating that a mere 4 hours of CO2 enrichment and potassium application can significantly improve the growth of cucumbers. And with the results of this study based on such a limited amount of CO2 enrichment time, imagine the good it could do for cucumber growth in the field when under 24 hours of CO2 enrichment!

Figure 1. Effects of elevated CO2 concentrations and increasing potassium concentrations on the total biomass on cucumber plants grown hydroponically in a greenhouse. AC = ambient CO2 concentration of 380 ppm; EC = elevated CO2 concentration of 1,000 ppm; K120 = potassium application of 120 mg L^-1; K240 = potassium application of 240 mg L^-1. Source: Adapted from Dabu et al. (2019).