Do hillslope position and rootstock matter in root water uptake by grapevines? A case study in a Tuscany vineyard, Italy

Understanding water availability and sources for crop transpiration is essential for sustainable management of water resources in agriculture, especially under changing climatic conditions. Identifying the origin of water accessed by crops is particularly critical in typical rain-fed agroecosystems, such as vineyards in Mediterranean regions where viticulture is one of the mainstays of the local economy.

As far as we know, no study so far has attempted to analyse root water uptake dynamics on hilly vineyards where the hillslope topography plays a role on water redistribution and availability for grapevine uptake. For this reason, we instrumented two plots within a vineyard in the famous Chianti wine region in Tuscany, Italy. The vineyard is cultivated with 11-year-old grapevines either on 1103 Paulsen or 420A rootstocks, which are typically characterized by a deeper and shallower rooting system, respectively. We aimed to test the hypothesis that i) grapevines located at the hillslope bottom took up water from shallower soil layers compared to grapevines located at the hillslope top due to lateral downslope redistribution of infiltrated rainwater; and that ii) grapevines with rootstock 1103 Paulsen took up water from deeper soil layers compared to the grapevines with rootstock 420A.

We monitored precipitation and temperature as well as soil moisture at 30 and 60 cm depth at two hillslope locations (top and bottom, 140 and 115 m asl, respectively) from April to October 2021. We collected samples for isotopic analysis from rainfall, soil at 30 and 60 cm, shoots and leaves from two adjacent grapevines for each rootstock at the two hillslope locations. Additional water samples were taken through the application of sealed plastic bags around some top branches and collection of water that had transpired and condensed on the bag walls. Water from soil samples, leaves and shoots was extracted though cryogenic vacuum distillation. The isotopic composition was determined through laser spectroscopy or, for organically-contaminated samples, mass spectrometry.

Preliminary results show that soil moisture was higher at the hillslope bottom than at the top, and higher at 60 than 30 cm depth. The isotopic composition of soil water was statistically different at the two depths with more enriched values in the shallower layer, as expected in Mediterranean climates; however, no statistical difference was observed between soil water at the two hillslope locations. The isotopic composition of plant water between the two locations was statistically different for bag (transpired) water and leaf water (although the latter was highly fractionated), but not for shoot water, allowing us only to partially accept hypothesis i). However, the isotopic composition of bag, leaf, and shoot water was always similar for 1103 Paulsen and 420A grafted plants, suggesting that grapevines with different rootstock took up soil water from the same depth in the study vineyard, and leading us to reject hypothesis ii).

These results contribute to better understand water uptake sources in economically-valuable agroecosystems such as vineyards.