Elevated CO₂ accelerates berry ripening only in high vigor rootstocks

Abstract

One of the key impacts of climate change in plants is the increase in atmospheric CO₂. In vineyards (Vitis vinifera), elevated CO₂ may alter phenology, yields and wine grape quality. Vigor control is a relevant factor in wine production and rootstocks are often selected for this trait to confer an adequate level of vigor to a given production system. However, the studies with different rootstock genotypes under elevated CO₂ are scarce. The objective of this experiment was to compare the response of grapevine plants grafted onto four rootstocks with different vigor to elevated CO₂ and to assess whether changes in the grape phenology, production and quality can be maintained by lower vigor rootstocks. Grenache plants grafted onto four rootstocks (from lower to higher vigor and drought tolerance: 420A, Fercal, 110R and 140 Ru) were grown under ambient (CA) or elevated CO₂ (800 ppm, CE) conditions. Total soluble solids were determined using a refractometer and the titratable acidity by performing titrations with NaOH until pH 7 was reached. The determinations of grape flavonoid profile was performed using HPLC-DAD and must amino acid concentration with HPLC-FLD. Plants under CE went through a photosynthetic acclimation as initially they had a higher assimilation rate but tended to level down with CA as stomatal closure took place. The accumulation of soluble solids was greater in high vigor rootstocks (110R and 140Ru) under CE conditions but negligible for lower vigor rootstocks (420A and Fercal). These trends in sugar accumulation were also observed in the loss of titratable acidity. 420A had a higher anthocyanin content under CE conditions, whereas the rest of the rootstocks had similar values. Our results suggest that berry ripening in lower vigor rootstocks may be less responsive to elevated CO₂. This was specially interesting for 420A, which even had a better berry color under elevated CO₂. However, an opposite trend was observed in amino acid concentration, whereby rootstock 420A under elevated CO₂ conditions accumulated a reduced concentration of amino acids. Although the use of low vigor rootstocks has an obvious problem related to their susceptibility to water stress, they have desirable traits that alleviate the effects of climate change.