Rootstocks modulate the physiology of the scion responses to water deficit in grapevines

In grapevine, rootstocks have been suggested as an option to cope with drought, one of the main effects of global warming. However, the rootstock effects on the scion at the stomata level remain unclear. This study aimed to investigate the effect of different 30-year-old rootstocks (1103P, R-110, 161-49C, 41B and 140Ru) growing in field conditions on ‘Tempranillo’ behaviour. Two irrigation levels (irrigation with 40% ET₀ and non-irrigation) were compared to distinguish any specific scion × rootstock interaction in response to water withholding. For this purpose, physiological parameters such as stomatal conductance (g_s) and photosynthesis (A_N) as well as the percentage of opened stomata and stomatal density were measured. Then, intrinsic water use efficiency (WUE_i) and whole-plant water conductivity (Kh_whole-plant) were calculated. Differences between drought and irrigation treatments were observed in all rootstocks. Individually, 1103P, 41B, and 140Ru showed the highest reductions in A_N and g_s under drought conditions as compared to irrigated plants, while 161-49C and R110 were the less responsive to water withholding. 1103P and R110 were the rootstocks with the highest and the lowest Kh_whole-plant, respectively. Interestingly, the rootstock 140Ru showed the highest percentage of opened stomata, both under well-watered and water stress conditions, while no differences were found in stomatal density neither between treatments nor between rootstocks. These results suggested a near-isohydric behaviour of the scion when growing with the rootstocks 161-49C and R110 and a near-anisohydric behaviour when growing with the rootstocks 1103P, 41B, and 140Ru. The latter kept their stomata more open in response to the water deficit than the former. This study emphasizes the importance of choosing the appropriate rootstock based on the specific land characteristics.