Assessing the use of shading to mitigate degradation of grape metabolic content in warm climates

Abstract

Global warming, and the ongoing expansion of viticulture to marginal areas is increasing the surface area of vineyards experiencing high solar irradiance and daily temperatures, leading to the loss of quality-related compounds. We studied the application of cluster-zone shading nets as a tool to ameliorate fruit microclimate and improve berry chemical composition in the warm and arid climate of the Negev desert. Shading-nets were placed around the cluster-zone with 30 and 60% shading intensities and different spectral properties (neutral, blue and red light enrichment) to control the light arriving to the clusters while minimizing the effect on whole plant physiology. We correlated continuous microclimatic measurements with fruit metabolite profiling and maturity indices. By harnessing the spatial structure of the grape-clusters, we obtained a large gradient of solar irradiance conditions. This allowed us to study the spatiotemporal patterns of grape primary and secondary metabolites under modified solar regime. Filtering solar irradiance lowered fruit temperature and improved the uniformity of microclimate conditions in the cluster-zone. Lower solar intensity was associated with lower levels of brach-chained amino acids and flavonols, but higher fruit weight, malate, flavan-3-ols, and overall anthocyanins. The latter revealed three distinct accumulation patterns, with malvidin anthocyanins and cyanidin-glucoside showing contrasting trends. Quercetin and kaempferol glucosides had a saturation-like logarithmic response to solar intensity, increasing cluster heterogeneity under low-light conditions. Taken together, our results indicate that careful regulation of solar intensity can mitigate the consequences of warm climate on fruit microclimate and effectively manipulate grape chemical composition.