**3.4 Impacts of elevated CO2 concentration**

Elevated atmospheric CO2 is usually favorable for plant growth as it causes an increased photosynthetic carbon fixation hence more biomass and yield. Free Air Carbon enrichment (FACE) experiments on agronomic crops such as wheat, rice and soybean have outlined 12–14% increase in harvestable yield owing to elevated carbon dioxide (eCO2) [134–136]. Although, there are limited studies on horticultural crops however, it has been indicated that eCO2 increased total antioxidant capacity of fruits and vegetables, along with higher concentration of glucose, fructose, total soluble sugars, polyphenols compounds, flavonoids, ascorbic acid, and calcium [90]. Research studies on grapevine related to eCO2 mainly focused on vegetative growth and photosynthetic responses while records on berry metabolism at physiological and molecular level are relatively scarce. However, most of the available records suggest an increase in photosynthetic activity hence better yield and biomass accumulation [94, 137–141]. Recently dependence of berry ripening rates on the carbon fixation was investigated however, only few quality attributes were found to be affected due to eCO2 and that particularly; sugars, acids, and berry size [138, 142, 143]. Recently, it has been inferred in FACE experiment that eCO2 did not negatively affected juice and wines quality [144]. Similarly, it had already been established that anthocyanins and proanthocyanidins were not affected by eCO2 [137, 138, 142–145]. Moreover, in multi stress experiments on cv. Temperanillo cuttings where elevated temperature condition i.e., +4°C and CO2 i.e., 700 ppm were simulated it was deduced that high CO2 in combination with elevated temperature hastened berry ripening and decreased high temperature tempted anthocyanin–sugar decoupling in berries [146].
