Ecohydrological dynamics and temporal water origin in European Mediterranean vineyards: a case study in Tuscany, Central Italy

Viticulture is an essential sector in agriculture as wine production plays a vital role in the socio-economic life of Europe. Grapevines are a valuable, long-lived species able to grow in hot and dry regions. We currently do not know whether grapevines entirely rely on deep soil water or they make substantial use of shallow water from summer precipitation events. Without knowing this, we poorly understand what fraction of summer precipitation inputs actually contributes to grapevine transpiration. This has implications for how we quantify grapevine-relevant precipitation budgets and for predicting the impacts of climate change on grape and wine production.

We investigated grapevine water use in a vineyard in the Chianti region, central Italy. During the growing season 2021, we monitored precipitation, temperature, and soil moisture at 30 and 60 cm depth. We collected over 250 samples for stable isotope analysis (hydrogen and oxygen) from rainfall, soil and plants. Since traditional plant water sampling is problematic for grapevines, we collected samples from shoots, leaves and from condensed leaf transpiration after sealed plastic bags were wrapped around some top branches. We use these alternative plant samples to reconstruct the isotopic signal in the xylem water and infer the plants’ seasonal water origin throughout the growing season.

Preliminary results show a progressive shift in the isotopic composition of sampled water. Precipitation samples fell on the Local Meteoric Water Line (LMWL) while soil samples deviated from it because of the effects of soil evaporation. The analysis of the seasonal origin of water revealed that soil water, and consequently xylem water, was mostly recharged during winter rainfall, consistently with the precipitation seasonal regime typically of the Mediterranean climate. The reconstructed xylem samples were generally less variable than soil water, indicating stable water sources, although in some occasion they were more spatially heterogeneous.  These results contribute to a better understanding of water interactions and uptake dynamics in important socio-economic agroecosystems such as vineyards.