Interactions between the vine water status and differential effects of organic and inorganic nitrogen application on grapevine physiology

In organic vineyards, nitrogen (N) and water deficit frequently occur concomitantly, but their interactions are poorly explored. This work aims to evaluate the effects of organic and inorganic N applications on the physiology of grapevines subjected to progressive water stress. In potted vines, the following treatments were compared: i. no N application (T1); ii. soil application of 3g of N as NH4NO3- (T2); foliar application of 3 g of N through protein hydrolysate (T3); combined soil application of 3g of N as NH4NO3- and 3g of protein hydrolysate (T4). All vines were individually subjected to water deficit from day of year (DOY) 170 to the achievement of a pre-dawn water potential (pdΨ) of -12 bars, and to a subsequent re-watering. The primary shoot growth was significantly affected by both organic and inorganic N supplementation, with T1 showing lower shoot lengths than other treatments from DOY 157. At the end of the experiment, T2 and T4 had a significantly higher total vine leaf area than T1 (5531 and 5331 vs 2487cm2/vine), with T3 setting at intermediate levels. T1 achieved a pdΨ of -12 bars later (DOY192 on average) than the other treatments (DOY186 pooling T2, T3 and T4). Correlations between pdΨ and gas exchange parameters show that T2, T3 and T4 maintained higher leaf photosynthetic rates (AN) at pdΨ <-4 bars. At varying stomatal conductance (gs), T2, T3 and T4 maintained a significantly higher leaf AN than T1, especially for gs > 0.15 mol/m2/s. T1 achieved stomatal closure at pdΨ ~-7 bars vs ~12 bars pooling T2, T3, and T4. At pdΨ >-0.4 Bars, T2, T3 and T4 exhibited significantly higher leaf proline concentration than T1, but at the peak of stress no differences were found between treatments, while T1 leaves had higher H2O2. Data demonstrates that N availability significantly interacts with vine water consumption and tolerance to water deficit. Foliar application of the organic N in the form of protein hydrolysates showed positive effects like soil mineral N application, and additive doses had minimal impact. Our study demonstrated that in organic vineyards, N fertilization can be implemented