Paper Reviewed
Arena, C. and Vitale, L. 2018. Chilling-induced reduction of photosynthesis is mitigated by exposure to elevated CO2 concentration. Photosynthetica 56: 1259-1267.

Multiple research studies have shown that elevated levels of atmospheric CO2 can alter important physiological processes to help lessen or fully ameliorate the negative impacts of high temperature stress on plants (see, for example, the many reviews we have posted on this topic in our Subject Index under the heading Temperature x CO2 Interaction). However, very little research has been conducted on the ability of higher levels of CO2 to reduce the negative impacts of cold temperature stress. Nevertheless, chilling, in the words of Arena and Vitale (2018), "represents a critical environmental stress that limits plant productivity and distribution in many regions of the world."

Typically, chilling adversely impacts key physiological processes. As noted by Arena and Vitale, for example, even a small drop in temperature, although it may not produce visible damage to a plant, can "induce up to [a] 50% reduction of plant productivity" by altering a plant's "water uptake, mineral nutrition, photosynthesis, respiration, and total metabolism." Given the large volume of research that demonstrates the benefits of elevated levels of atmospheric CO2 on these processes, the two Italian researchers therefore set out to examine "the role of elevated CO2 concentrations in mitigating chilling-induced photosynthetic depression in Beta vulgaris L., a winter crop widely cultivated in the Mediterranean ago-ecosystems."

To accomplish this objective, Arena and Vitale grew chard (B. vulgaris cv. Cicla) in a controlled-environment at the Department of Biology of the University of Naples Federico II, Italy, under well-watered and fertilized conditions. At the time of their experiment, groups of plants were exposed to one of four five-hour treatments: (1) ambient CO2 (360 ppm) and ambient temperature (25°C), (2) elevated CO2 (700 ppm) and ambient temperature (25°C), (3) ambient CO2 (360 ppm) and low temperature (4°C), (4) elevated CO2 (700 ppm) and low temperature (4°C). During and following the short-term treatment, multiple measurements were made on key processes relating to photosynthesis so as to determine if elevated CO2 was able to reduce the impacts of chilling stress.

The results of this phase of their study indicated that in response to chilling stress, plants in the elevated CO2 treatment exhibited higher values of CO2 fixation, photochemical activity and Rubisco amount than plants exposed to ambient CO2. According to Arena and Vitale, the reason for this difference was two-fold: (1) under ambient conditions, the "increase of thermal dissipation processes was not adequate to guarantee the PSII photoprotection and the phososynthetic recovery after chilling," whereas (2) "the elevated CO2 concentration in combination with low temperature exerted a mitigating effect on reduction of Rubisco content induced by chilling," which allowed leaves "to maintain higher photosynthetic rates and reduce the adverse effect of low temperature on Rubisco oxygenase activity, upon return to prechilling conditions." Consequently, Arena and Vitale conclude that their study reveals "the positive effect of elevated CO2 in mitigating chilling stress."