Paper Reviewed
Esmaili, M., Aliniaeifard, S., Mashal, M., Ghorbanzadeh, P., Seif, M., Gavilan, M.U., Carrillo, F.F., Lastochkina, O. and Li, T. 2020. CO2 enrichment and increasing light intensity till a threshold level, enhance growth and water use efficiency of lettuce plants in controlled environment. Climate Dynamics 44: 3469-3479.

It has long been recognized that rising atmospheric CO2 concentrations are enhancing plant growth across the world. However, much remains to be learned about the interaction of elevated CO2 and other key factors contributing to plant growth. In their recent work Esmaili et al. (2020) focused on light intensity, studying its combined effects with CO2 on lettuce (Lactuca sativa, cv. Partavousi). Specifically, they wanted to learn the impacts of these two parameters on lettuce growth, leaf and stomatal characteristics, evapotranspiration and water use efficiency.

The experiment was conducted in environment-controlled growth chambers under a full-factorial design with four light intensities (75, 150, 300 and 600 PPFD) and four CO2 concentrations (400, 800, 1200 and 1600 ppm). Adequate water and nutrients were supplied and the experiment lasted 40 days.

In describing their findings, Esmaili et al. say "plants exposed to higher light intensities and CO2 concentrations had better growth performance than those exposed to lower light and CO2 levels." Indeed, as shown in Figure 1 below, individual lettuce leaf dry weights averaged approximately 1 g, 2.5 g, 6 g and 7 g under 75, 150, 300, and 600 PPFD of light intensity. And, within each light intensity treatment, elevated CO2 raised the lettuce dry weight from 25% to 148%.

Elevated level of CO2 and increased light intensity also positively impacted lettuce leaf area and plant water use efficiency (WUE). In the case of WUE, the authors report it was "two times higher" at the two highest CO2 concentrations (1200 and 1600 ppm) compared to ambient (400 ppm), and it likely benefitted from CO2-induced enhancements of leaf photosynthesis and declines in stomatal pore aperture. Consequently, in light of all of the above, Esmaili et al. conclude "increasing light intensity and CO2 concentration resulted in better growth performance in lettuce plants." And by incorporating their results into better management practices, the commercial greenhouse industry will witness greater lettuce yields than they are at the present time.

Figure 1. Impact of different light intensities and CO2 enrichment on the leaf dry weight of lettuce after 40 days of growth. The percentages in red text indicate the increase in lettuce dry weight due to CO2 at a given light intensity, relative to the control concentration of 400 ppm. Adapted from Esmaili et al. (2020).