Rootstock differences in soil-water uptake during drying-wetting cycles imaged with 3d electrical resistivity tomography

Abstract

Context and purpose of the study – Limited knowledge has been acquired on grapevine roots and rhizosphere processes because of harder access when compared to aerial parts. There is need for new methods to study root behavior in undisturbed field conditions, and relate these effects on canopy and yield. The aim of this multidisciplinary study was to image and quantify spatial-temporal differences in soil-water uptake by genetically different rootstocks and to assess the response of the canopy during drought and rewetting.

Material and methods – During two years, three replicates of 10 plants of Chardonnay, 5 plants grafted onto 110R and 5 on 101-14 Mgt, were monitored in a drip-irrigated experimental vineyard. Each experimental unit was equipped with time-domain reflecrometer sensors for continuous measurement of soil water and with stainless-steel rods and micro-borehole electrodes for time-lapse 2D and 3D electrical resistivity tomography (ERT). The soil profile was described with soil pits at both ends of the experimental units and sampled for physical-chemical analysis. Grapevine water status of each vine was monitored routinely with 3h-lag diurnal cycles of water potentials and leaf gas-exchanges (from predawn to following night) and δ13C at harvest. Light and Ci photosynthesis response curves, predawn Fv/Fm were measured under dry and wet conditions. Grape composition, yield components and pruning-weights were also measured.

Results – Different models were tested to develop a pedotransfer function and transform electrical resistivity into soil volume wetness. Due to the sandy nature of the soil the Archie law performed well and was used to map water depletion in 3D with an error of 1.2 %vol., R2 = 0.73 (measured on an independent test set). Before rewetting the grapevine experienced severe drought stress in both years of the study (< – 10MPa in predawn), and amount of soil water per vine was significantly correlated to single plant water potentials and to canopy size. One fold differences in the amount of soil water absorbed by the two rootstocks were reached at the end of the drought period, with distinct spatial patterns. The 110R was more conservative, and soil depletion was localized in space around each vines, while the 101-14 was less conservative and more homogenously and deeply depleted the soil profile affecting whole plant water status and leaf physiology that was more depressed. Replenishment of the fraction of transpired soil water by drip irrigation was imaged by time-lapse ERT, and differences were observed in the reaction to rewetting by the two rootstocks.