Background
The authors write that high temperature during summer months "is a primary factor limiting the growth of C3 cool-season plant species, as temperatures often exceed the optimal range of 10 to 24°C for shoot and root growth during these months in many areas," citing DiPaola and Beard (1992). And they add that "elevated temperature is becoming an increasingly significant abiotic stress in the scenario of global climate change."

What was done
To explore this situation experimentally, Song et al. propagated well watered and fertilized Kentucky bluegrass (cv. 'Baron') plants in pots filled with fritted clay, which they ultimately transferred to growth chambers where the potted plants were maintained in air of either 400 or 800 ppm CO2 concentration and subjected to five different day/night temperature regimes: 15/12, 20/17, 25/22, 30/27 or 35/32°C.

What was learned
The three researchers report that the doubling of the air's CO2 concentration they employed promoted net photosynthesis by boosting it by an average of 109% across the different levels of temperature, as well as shoot and root growth (the latter of which was greater than the former), under all levels of temperature, while it mitigated the adverse effects of severe high temperatures (30 and 35°C). In addition, they say that the elevated CO2 led to a "reduction in leaf respiration by 32, 43, 37, 20 and 33% at 15, 20, 25, 30 and 35°C, respectively." And as an added bonus, they discovered that the elevated CO2 treatment "resulted in a significantly higher content of glucose (by 144%) at 30 and 35°C, sucrose content (by 55%) at 30°C, fructose content (by 80%) and mannobiose content (by 254%) at 35°C, and galactose content (by 80%) at 20, 25 and 30°C, when compared to ambient CO2 conditions."

What it means
Among a number of other things, Song et al. suggest that "more enhanced root growth relative to shoot growth by elevated CO2 could facilitate water and nutrient uptake by the root system to support plant growth and survival under high temperature stress," such as they feel could occur sometime in the not-too-distant future via the scary scenarios predicted by legions of climate alarmists.

Reference
DiPaola, J.M. and Beard, J.B. 1992. Physiological effects of temperature stress. In: Waddington, D.V., Carrow, R.N. and Shearman, R.C. (Eds.). Turfgrass. Agronomy Monograph 32. American Society of Agronomy, Madison, Wisconsin, USA, pp. 231-262.