Future Atmospheric CO2 Concentrations and Heat Wave Effects on Lentil (Lens culinaris): A FACE Experiment.

Future atmospheric CO₂ concentrations are expected to increase from current levels of approximately 400 µmol mol^-1 to 550 µmol mol^-1 by 2050. This increase in the substrate of photosynthesis has direct implications for plant metabolism, such as increased growth and yield, at least in C3 plants and in the absence of changes in temperature and rainfall patterns. However, as atmospheric CO₂ is a major driver for global warming, it is predicted that the frequency and the duration of heat waves will continue to increase. Lentil is a cool-season crop whose production has recently expanded into areas where it is subject to water and high temperature stress by pod filling (e.g. Australia). The effects of elevated atmospheric CO₂ concentrations (e[CO₂]) (imposed by Free Air CO₂ Enrichment (FACE)) were evaluated on six cultivars of lentil in 2013-2014 and two cultivars in 2015. Additionally, root length was observed with mini-rhizotrons in two cultivars in 2014-2015, and these were also subject to a 3-day heat wave (~ 40^oC) imposed at the flat pod stage. Grain yield was increased on average by 42% by e[CO₂], but reduced 22% by the heat wave. The effects of the heat wave appear worse under future [CO₂] concentrations as it led to a proportionally greater decrease in the number of grains per m² due to the heat wave compared with growth at ambient [CO₂]. New results pertaining to root length and nitrogen fixation under e[CO₂] will also be presented.