Stable isotopes as tracers of the effects of vineyard management practices

Soil water management in Mediterranean vineyards is increasingly critical under increasing aridity. Soil management practices such as cover crops are promoted for improving soil structure, reducing erosion, and enhancing ecosystem services. However, grapevine production is often reduced under cover crops, and their effects on vine water use are still not fully understood. Here, we investigated the impact of soil management, i.e. conventional tillage vs. spontaneous cover crop, on the soil–plant–atmosphere continuum of a rainfed vineyard in Rioja Alavesa during veraison, with the aim of contributing to the ongoing discussion on soil management effects on vine water use.

Determining root water uptake depth using water isotopes (δ¹⁸O and δ²H) revealed contrasting uptake strategies between conventional tillage and spontaneous cover crop. Building on that, we focused on aboveground responses by combining measurements of vine water status (midday leaf water potential, Ψₘ) with stable isotopes of carbon, oxygen, and nitrogen (δ¹³C, δ¹⁸O, and δ¹⁵N) in leaves and berries. The Ψₘ values showed a clear management effect, with vines under cover crop exhibiting improved water status compared to vines under tillage (Ψₘ= -0.62 and -0.83 MPa respectively, p < 0.01). Leaf δ¹⁵N also differed between treatments, indicating changes in nitrogen availability or uptake associated with soil management (mean leaf δ¹⁵N under cover crop = 2.14‰ and tillage = 0.15‰, p < 0.01). In contrast, leaf δ¹⁸O and berry δ¹³C showed substantial plant-to-plant variability with no consistent treatment effect (p = 0.22 and 0.51, respectively).

Taken together, our results show that cover crops can enhance vine hydraulic status (Ψₘ) and modify nitrogen dynamics (δ¹⁵N), without altering long-term carbon assimilation efficiency (δ¹³C and δ¹⁸O). They also demonstrate that soil management effects are strongly dependent on the temporal scale of observation, as instantaneous indicators (Ψₘ) revealed treatment differences that were not captured by seasonally integrated isotopic signals (δ¹³C and δ¹⁸O). Overall, our study highlights the value of combining hydraulic measurements with multiple stable isotopes to improve the assessment of sustainable soil and water management strategies in vineyards.