Effect of Elevated CO2 and Temperature on Plants with Different Type of Photosynthesis: Quinoa (C3) and Amaranth (C4)

Abstract

The thermal stability of plants with different types of photosynthesis Chenopodium quinoa Willd. (C3) and Amaranthus retroflexus L. (C4-NAD) to short-term elevated temperature (35°С, eT) at ambient (400 ppm, aCO2) and elevated (800 ppm, eCO2) CO2 concentration was investigated. Growth parameters, water, proline, and MDA content, CO2/H2О gas exchange parameters, the functioning of PS I and PS II, and the content of key photosynthetic (Rubisco, PEPC) and photorespiratory (GDC) enzymes were analyzed. Under control conditions, C4-type plants, compared with the C3-type, show higher values of dry biomass growth, intensity of visible photosynthesis, transpiration, and PS I activity and lower proline content. The photosynthetic and stomatal apparatus of both types was sensitive to eT, which manifested itself in a decrease in the intensity of apparent photosynthesis and transpiration. In addition, suppression of light reactions (PS II) and intensity of photorespiration (according to GDC) was observed in the C3-species and an increase in the content of proline in the C4-species. Under eCO2 conditions, the C3-species showed a decrease in the intensity of photorespiration, while oxidative stress (twofold increase in the content of MDA) was accompanied by reduced intensity of apparent photosynthesis, transpiration, and increased intensity of dark mitochondrial respiration in the C4-species. A softening effect of eCO2 on thermal stability data for C3- and C4-plants was not established. With the combined action of eCO2 and eT, both types exhibited oxidative stress, reduced efficiency of PS II and apparent photosynthesis, and activation of dark respiration. However, differences were also observed: oxidative stress was accompanied by a decrease in the increase in dry biomass and water content in tissues, as well as suppression of photorespiration, in the C3-species, while there was a decrease in the intensity of transpiration and an increase in the content of PEPC in the C4-species. Reduced WUE with combined action of eCO2 and eT in plants of the C4-species was less significant than the C3-species. The different response of quinoa plants (C3) and amaranth (C4) on the combined effect of climatic factors of elevated temperature and CO2 concentration is discussed.