Abstract
Plant-based sensors able to continuously measure the stem water potential could be useful for the early detection of water stress, having the advantage of overcoming the labour-intensive and destructive procedures needed to assess water potential with the traditional pressure chamber. The experiment aimed to test the efficacy of microtensiometers to characterize grapevines’ water status response to the increasing limitation of soil water availability. To this purpose, four Florapulse microtensiometers were applied to 4 potted grapevines (‘Pinot gris’ on SO4) growing under controlled conditions mimicking typical summer days. Plants were constantly weighted to assess transpiration gravimetrically. Two consecutive cycles of water stress were imposed by withholding irrigation for 10 days. During this period, midday stem and pre-dawn water potential were periodically assessed using the traditional pressure chamber. The vines developed a different canopy surface, with leaf area ranging from 1.19 (pot 4) and 1.55 (pot 1 and 2) m2 vine-1, and thus responded differently to the absence of irrigation. The first stress cycle caused the loss of 42, 25, and 49% of the leaves in pots 1, 2, and 3, respectively, while no visible symptoms were observed in pot 4. The two microtensiometers that provided a complete data set during the whole experiment clearly detected the diurnal course and the daily trend of plant water potential. The maximum and minimum daily values extracted from the continuous time series were used as a proxy of pre-dawn and midday stem water potential, respectively. They were consistently 0.2 MPa higher (on average) than stem water potential values obtained using the pressure chamber. Microtensiometer data were well correlated with daily transpiration. The same values, binned in classes of 0.1 MPa were used to characterize the water use strategy through the slope metric, evidencing a strict anisohydric behaviour of ‘Pinot gris’ even under severe water limiting conditions (<-1.0 MPa of midday stem water potential).