Yishai Netzer

A non‐invasive probe for online‐monitoring of turgor pressure changes under field conditions

An advanced non-invasive, field-suitable and inexpensive leaf patch clamp pressure probe for online-monitoring of the water relations of intact leaves is described. The probe measures the attenuated output patch clamp pressure, P(p), of a clamped leaf in response to an externally applied input pressure, P(clamp). P(clamp) is generated magnetically. P(p) is sensed by a pressure sensor integrated into the magnetic clamp. The magnitude of P(p) depends on the transfer function, T(f), of the leaf cells. T(f) consists of a turgor pressure-independent (related to the compression of the cuticle, cell walls and other structural elements) and a turgor pressure-dependent term. T(f) is dimensionless and assumes values between 0 and 1. Theory shows that T(f) is a power function of cell turgor pressure P(c). Concomitant P(p) and P(c) measurements on grapevines confirmed the relationship between T(f) and P(c). P(p) peaked if P(c) approached zero and assumed low values if P(c) reached maximum values. The novel probe was successfully tested on leaves of irrigated and non-irrigated grapevines under field conditions. Data show that slight changes in the microclimate and/or water supply (by irrigation or rain) are reflected very sensitively in P(p).

Sustained and regulated deficit irrigation of field‐grown Merlot grapevines

Background and Aims The aim of this research was to examine the effect of sustained and regulated deficit irrigation regimes on vegetative growth, physiological aspects and yield parameters of field-grown Merlot grapevines. Methods and Results The 4-year trial (2009–2012) in a 13-year-old commercial vineyard of Vitis vinifera cv. Merlot compared the following irrigation treatments: three sustained deficit irrigation treatments and two regulated deficit irrigation treatments. We measured leaf area index and pruning mass to assess vegetative growth, and we recorded stem water potential and gas exchange parameters to examine vine water status. At harvest, we measured yield parameters, crushed berries and analysed must. High water availability during early berry development enhanced vegetative growth and increased berry size and yield. Reducing water supply in order to create a certain level of drought stress during late berry development did not damage yield or berry maturation. Conclusions Regulated deficit irrigation treatment combining higher irrigation from flowering to bunch closure and lower irrigation from bunch closure to harvest has the potential to generate the best balance between vegetative growth, high yield and wine with enhanced colour and aroma compounds. Significance of the Study This study demonstrates the implications of skilled irrigation, in particular the specific effect of irrigation alternation at different phenological stages.

Grapevine Anatomy as a Possible Determinant of Isohydric or Anisohydric Behavior

Isohydric plants maintain constant water potential through rapid stomatal closure, whereas anisohydric plants only close their stomata at very low water potentials. However, distinctions between isohydric and anisohydric behaviors among different cultivars of the same species are unclear. This study compared the physiological response to prolonged drought stress in the isohydric Grenache and the anisohydric Shiraz cultivars of the Vitis vinifera species. Plants were exposed to 60-day periods of deficit irrigation (25% of plant water consumption under well-watered conditions) during the summers of 2011 and 2012. Physiological measurements, water potential, leaf gas exchange, canopy area, leaf senescence, stem characteristics, and morphological characteristics were analyzed. Stomatal conductance was consistently lower in Grenache than in Shiraz at all values of midday stem and predawn leaf water potentials, respectively. The Shiraz plants exhibited greater vegetative growth and less defoliation than the Grenache plants in response to water deficit. Anatomical architecture analyses revealed that Grenache plants had greater xylem vessel diameter, hydraulic conductivity, and stomatal density than the Shiraz plants. These results suggest isohydric and anisohydric behaviors may be well-defined, time-regulated responses rather than distinct mechanisms that plants use to cope with drought stress. The rapid response to water deficit exhibited by isohydric plants may be because they are more vulnerable to fatal xylem embolisms than anisohydric plants. Thus, the accelerated response allows isohydric plants to avoid drought stress and minimize risk of xylem cavitation, but may lower the plant’s ability to survive moderate stress of prolonged drought.

From structural constraints to hydraulic function in three Vitis rootstocks

Key messageNarrow stem size in limitingVitisrootstocks imposes a morphological constraint on the scion via reduced annual ring size, and thus reduces hydraulic conductivity and subsequently physiological performance and yield.AbstractGraft is a union between two separate species or cultivars, which produces a chimera plant with new qualities—as rootstock affects scion growth, yield, and adaptability to different environmental conditions. In Vitis, it is possible to generate rootstock/scion combinations that produce a desired drought stress effect crucial for high-quality wine production, though the mechanisms for such interactions are complex and poorly understood. The current study was done on vines with an identical scion (Vitis vinifera ‘Cabernet Sauvignon’) grafted on three different rootstocks—either Riparia Gloire, Paulsen 1103 or 420A—in attempt to explain the differences in water status by examining the underlying anatomical constraints and calculated theoretical hydraulic conductivity. There was a significant difference in physiological responses and yield between the grafts. Riparia Gloire grafts had the lowest water potentials and the highest quality grapes, together with low root, scion stem, and branch theoretical hydraulic conductivity. In scions grafted on Riparia Gloire, the annual growth rings were significantly narrower than in the other two grafts, causing a significantly lower theoretical hydraulic conductivity per annual ring. The narrow annual ring size in scion stem was imposed by the morphological constraint of the stem size. In hydraulically inferior Riparia Gloire grafts, the difference was disproportionally large, with a wide scion grafted on a very narrow rootstock, and Paulsen 1103 had the smoothest graft union. Our results indicate that the ability to develop stronger drought stress in Vitis grafts depends on rootstock-imposed morphological restriction of hydraulic conductivity.

Sodium and Chloride Distribution in Grapevines as a Function of Rootstock and Irrigation Water Salinity

The salt tolerance of rootstocks is often assessed based on their ability to limit uptake of sodium (Na) and chloride (Cl) ions. Here, we evaluated the effects of three irrigation salinity levels (electrical conductivity of 1.2, 2.7, and 4.2 dS/m) on Cabernet Sauvignon grapes grafted on Ruggeri, Paulsen, 216/3, and 101/14 rootstocks. Growth parameters were affected by salinity level but not by rootstock, and yield was not affected by either variable. Ruggeri and 216/3 were most effective at limiting uptake and accumulation of Na and Cl in scion petioles, wood, and must. The rootstocks differentially excluded Na and Cl from vines; 216/3 and Ruggeri showed the best performance for Na and Cl, respectively. More Na than Cl accumulated in woody tissue. Mortality rates as high as 17.5% were found for poor salt-excluding rootstocks irrigated with the highest salinity water. The apparent breakdown of tolerance mechanisms, leading to salt damage and vine mortality, might be due to Na reaching critical levels in woody tissues. The ability to exclude Na and Cl from shoots and fruit was found to (a) increase wine quality by reducing concentrations of salt ions in must and wine, and (b) reduce mortality rates that result from long-term exposure to salt.

Water availability dynamics have long-term effects on mature stem structure in Vitis vinifera

PREMISE OF THE STUDY The stem of Vitis vinifera, a climbing vine of global economic importance, is characterized by both wide and narrow vessels and high specific hydraulic conductivity. While the effect of drought stress has been studied in 1- and 2-yr-old stems, there are few data documenting effects of drought stress on the anatomical structure of the mature, woody stem near the base of the vine. Here we describe mature wood anatomical responses to two irrigation regimes on wood anatomy and specific hydraulic conductivity in Vitis vinifera Merlot vines. METHODS For 4 years, irrigation was applied constantly at low, medium, or high levels, or at alternating levels at two different periods during the growing season, either early spring or late summer, resulting in late season or early spring deficits, respectively. The following variables were measured: trunk diameter, annual ring width and area, vessel diameter, specific hydraulic conductivity and stem water potential. KEY RESULTS High water availability early in the season (late deficit) resulted in vigorous vegetative growth (greater trunk diameter, ring width and area), wider vessels and increased specific hydraulic conductivity. High water availability early in the season caused a shift of the vessel population towards the wider frequency classes. These late deficit vines showed more negative water potential values late in the season than vines that received low but relatively constant irrigation. CONCLUSIONS We concluded that high water availability during vegetative growth period of Vitis increases vessels diameter and hydraulic conductivity and causes the vines to be more vulnerable to drought stress late in the season.

Using Time Series of High-Resolution Planet Satellite Images to Monitor Grapevine Stem Water Potential in Commercial Vineyards

Spectral-based vegetation indices (VI) have been shown to be good proxies of grapevine stem water potential (Ψstem), assisting in irrigation decision-making for commercial vineyards. However, VI-Ψstem correlations are mostly reported at the leaf or canopy scales, using proximal canopy-based sensors or very-high-spatial resolution images derived from sensors mounted on small airplanes or drones. Here, for the first time, we take advantage of high-spatial resolution (3-m) near-daily images acquired from Planet’s nano-satellite constellation to derive VI-Ψstem correlations at the vineyard scale. Weekly Ψstem was measured along the growing season of 2017 in six vines each in 81 commercial vineyards and in 60 pairs of grapevines in a 2.4 ha experimental vineyard in Israel. The Clip application programming interface (API), provided by Planet, and the Google Earth Engine platform were used to derive spatially continuous time series of four VIs—GNDVI, NDVI, EVI and SAVI—in the 82 vineyards. Results show that per-week multivariable linear models using variables extracted from VI time series successfully tracked spatial variations in Ψstem across the experimental vineyard (Pearson’s-r = 0.45–0.84; N = 60). A simple linear regression model enabled monitoring seasonal changes in Ψstem along the growing season in the vineyard (r = 0.80–0.82). Planet VIs and seasonal Ψstem data from the 82 vineyards were used to derive a ‘global’ model for in-season monitoring of Ψstem at the vineyard-level (r = 0.78; RMSE = 18.5%; N = 970). The ‘global’ model, which requires only a few VI variables extracted from Planet images, may be used for real-time weekly assessment of Ψstem in Mediterranean vineyards, substantially improving the efficiency of conventional in-field monitoring efforts.