In situ grapevine hydraulic response to drought is soil-texture specific

Climate change will exacerbate drought events in many regions, increasing the demand on freshwater resources and creating major challenges for viticulture. The knowledge on grapevine drought stress physiology has increased significantly in recent years, but a holistic comprehension on how soil-grapevine hydraulic conductances develop and are regulated in the soil-grapevine-atmosphere continuum (SPAC) remains poorly understood. In particular, how soil type affects the grapevine hydraulic response to drought is still an open question.

The aim of this work is to understand how the hydraulic conductances in the SPAC continuously evolve according to soil type, during drought.

The continuous, concomitant and automatic monitoring of soil and collar water potentials, as well as sap flow, made it possible to characterize the evolution of the soil-grapevine hydraulics in situ in real-time. To investigate the impact of the soil type, two vineyards planted with Vitis vinifera cv. Chardonnay were selected due to their intra-field heterogeneity of soil properties (two subplots per vineyard). In a first vineyard, soil-grapevine hydraulics were measured on a sandy subplot and on a loamy subplot. In a second vineyard, we worked on a loamy subplot and on a silty-clay subplot.

We found that grapevine hydraulic response to soil drying is soil texture specific. Stomatal closure was observed for grapevines planted on coarse-textured soils, but not, or little, on fine-textured soils. This stomatal response was triggered by a decrease in belowground hydraulic conductance and not xylem cavitation in the trunk. This suggests that the interaction between the grapevine and the soil hydraulic environment plays a crucial role in shaping hydraulic behaviour of Chardonnay during drought periods.

While soil dries out, the decline in soil hydraulic conductivity led to a steep and nonlinear reduction in soil matric potential at the soil-root interface, with greater reduction in sandy soils compared to loamy soils. This rapid decline in soil hydraulic conductivity implies that the soil is more rapidly limiting (at less negative soil water potential), triggering earlier stomatal closure in coarse-textured soils. Stomatal regulation is amplified in sandy profile as compared to fine textured profile within the same grape variety.