Gas exchange, vine performance and modulation of secondary metabolism in Vitis vinifera L. cv Barbera following long-term nitrogen deficit

Main Conclusion A reprogramming of secondary metabolism to acclimate to nitrogen deficiency was seen in grapevine eliciting an accumulation of strigolactones and jasmonate. This response links with photosynthetic compensation and enhanced ripening. In addition to the metabolism directly related to nitrogen assimilation, long-term nitrogen depletion may affect plant secondary metabolism, in turn affecting grapevine performance. In this work, the effect of nitrogen deficit was investigated in V. vinifera cv. Barbera potted vines following three years of deprivation, using a combination of morpho-physiological assessments and mass spectrometry-based untargeted metabolomics. Plants grown under nitrogen limitation showed reduced growth and even more curtailed yields, lowered SPAD values, and a quite preserved leaf gas exchange, compared to plants grown under non-limiting nitrogen availability. Ripening was decidedly accelerated, and berry composition improved in terms of higher sugar and phenolic contents under nitrogen-limiting conditions. Metabolomics showed the broad involvement of secondary metabolism in acclimation to nitrogen deficiency, including a distinctive modulation of the phytohormone profile. Several nitrogen-containing metabolites were down accumulated under nitrogen-limiting conditions, including alkaloids, glucosinolates, hypoxanthine, and inosine. On the other hand, phenylpropanoids showed an accumulation trend. Concerning the recruitment of hormones, nitrogen deprivation elicited an accumulation of strigolactones and jasmonate. Noteworthy, both strigolactones and jasmonates have been previously related to increased photosynthetic efficiency under abiotic stress. Furthermore, the severe reduction of lateral shoot development we recorded in N-deprived vines is consistent with the accumulation of strigolactones. Overall, our results suggest that nitrogen deprivation induced a rather broad metabolic reprogramming, mainly including secondary metabolism and hormones profile, reflected in the modulation of photosynthetic performance, canopy growth, and possibly fruit quality.

Ground Truthing and Physiological Validation of Vis-NIR Spectral Indices for Early Diagnosis of Nitrogen Deficiency in cv. Barbera (Vitis vinifera L.) Grapevines

Several narrow or broadband spectral indices can be calculated at varying spatial and spectral resolution, which can then be correlated with the physiological and nutritional status of the leaves. In a three-year trial carried out on fruiting, potted cv. Barbera grapevines subjected to full (N+) or no (N0) nitrogen supply, seasonal evolution of different leaf spectral indices were correlated with non-destructive chlorophyll readings (Minolta SPAD meter), leaf gas exchange, and vine performance. Throughout the entire trial, N starvation resulted in greater-than-proportional limitation of vine yield as compared to vegetative growth (55% compared to 26% less than values measured on N+). Indices calculated within the red-edge spectral domain had highest sensitivity to relative change between N+ and N0, also indicating that the promptest response was recorded at the median shoot zone level. Twelve broadband indices were linearly correlated with leaf blade N concentration at veraison, indicating that N values ≤ 1.8% of dry matter identify a limiting N status. Any of these indices collected at the leaf level can be reliably used as a non-destructive predictor of N availability, albeit due to significant between-year variation in their absolute values at a given N level, readings should always include a well-supplied N treatment.

Role of natural terroir attributes on Barbera grapevine performance and grape quality in Piemonte region (Italy)

The trial was carried out in the Bersano estate (Nizza Monferrato, Piemonte, Italy) in different vineyards (Generala, Cremosina and Monteolivo) devoted to the production of DOCG Nizza, the newest and highly reputed Barbera denomination. For Bersano, this research provided access to scientific information and tools to valorise its Nizza wines and to characterize and select some sub-zones. The study investigated the effect of natural terroir attributes on vine behaviour and grape composition of cv. Barbera. Conducted in 2017, the tests included phenological phases, vegetative growth, chlorophyll and gas exchange measures. Maturation curves were also developed to better understand the time course of berry ripening, from fruit-set to harvest and statistical relationships were studied. The vineyards presented different climatic and soil conditions which influenced bud burst, shoot growth and plant photosynthesis; concerning soil properties, texture was the main differentiating factor. During the growing season, the berries followed the normal growth pattern, but an extreme drop occurred at harvest due to high diurnal temperatures. Ripening curves showed dissimilarities between the three studied vineyards, i.e. TSS, berry mass, total anthocyanins and total phenols. La Generala presented the best viticulture features regarding the vine performance and grape composition.