Unexpected relationships between vine vigor and grape composition in warm climate conditions

摘要

Aim: The purpose of the research was to link vigor with grape composition in a climate change scenario.Methods and results: This work presents a 4-year study (from 2010 to 2013) in a non-irrigated Tempranillo vineyard located in La Rioja (Spain). It is based on the acquisition of multi-spectral imagery at véraison and a subsequent zoning in two different vigor zones based on NDVI (Normalized Difference Vegetation Index). All parameters related to vigor showed significant differences within the zones (total shoot length, leaf area, pruning weight). Unexpectedly, the content in anthocyanins was found to be higher in the highest vigor zone in most of the years of study, a point particularly?discussed in this work.Conclusion: Climatic conditions may affect considerably bunch microclimate and disturb the biosynthetic pathways of major grape components, leading to maturation mismatches. In hotter years, high vigor vines may favor anthocyanin accumulation through shading and protecting effects in the bunch area.Significance and impact of the study: Many studies have shown a negative relationship between vigor and grape anthocyanins, but in the present research the opposite trend was observed in hot years. IntroductionVineyard spatial variability has always concerned grape growers and has been considered in many recent researches in viticulture. The sources of this variation involve climate, land (topography and soil composition, including water and nutrient availability), and diseases. Previous research has focused on vine vegetative expression and vigor variability, but also on yield and grape characteristics (Tisseyre et al., 2008; Bramley et al., 2011; Arnó et al., 2012).One of the most easy, fast and feasible tools to assess vineyard variation is remote sensing. Spectral sensors mounted on satellites, or cameras in airplanes or drones, collect information of vegetation reflectance in a range of wavelengths. These data are translated into a single number or index, the most commonly used being the NDVI (Normalized Difference Vegetation Index), which involves infrared and near-infrared wavelength (Rouse et al., 1974). NDVI provides accurate information about photosynthetically active biomass and canopy size (Dobrowski et al., 2003; Hall et al., 2003; Johnson et al., 2003), that is, vegetative expression. Authors have tried to assess NDVI as a predictor of other vineyard characteristics, such as yield (Proffitt and Malcolm, 2005) and grape composition, specially anthocyanins and polyphenols (Johnson et al., 2003; Lamb et al., 2004; Bramley, 2005; Hall et al., 2011; Fiorillo et al., 2012; Martinez-Casasnovas et al., 2012), with variable results.The effort to relate NDVI as a predictor of grape composition has not always been successful since the factors influencing grape quality are numerous and complex. It is assumed that the ratio between leaf area and yield needs to reach a minimum threshold to assure proper ripening (Kliewer and Dokoozlian, 2005). In this concern, vegetation indices could give valuable information. Regarding anthocyanins, their synthesis and accumulation is highly dependent on temperature and light. In this respect, most of the studies relating vigor and grape quality have revealed that high vigor vines present less anthocyanin content than low vigor vines (Lamb et al., 2004; Stamatiadis et al., 2006; Cortell et al., 2007; Hall et al., 2011; Martinez-Casanovas et al., 2012; Filippetti et al., 2013). This may be explained by the fact that most of these studies have been carried out in rather cold climates, where bunch light exposure and temperature are limiting factors. Moreover, these studies usually analyze anthocyanins in terms of concentration (mg/kg or mL/kg), so berry size has a major influence on these values. Anthocyanins being only present in the skin, the smaller the berry, the smaller the volume (and liquid phase), and thus the higher the skin:pulp ratio, leading to higher anthocyanin concentrations in the obtained musts (Coombe and Iland, 2004). Then, it would be more appropriate to consider absolute anthocyanin synthesis (for instance, mg/cm2 of skin) for a better comprehension of the synthesis of this compound from a plant physiological point of view. Besides, climate is facing a global warming in which grape growing regions boundaries are changing, and predictions reveal an increase of about +2.5°C in the next decades (IPCC, 2007). Temperate and warm climates are experiencing unusual temperature increases, causing decoupling between sugars and anthocyanins and altering their accumulation and degradation pathways (Schultz and Jones, 2010).Thus, several studies reveal that anthocyanin synthesis positively depends on temperature, but it is restrained by temperatures above 26°C (Kliewer and Torres, 1972; Iland and Gago, 2002; Sadras and McCarthy, 2007). Temperatures above 30°C may lead to less concentration in anthocyanins by impairing their biosynthetic pathways and promoting their