Does predawn water potential discern between irrigation treatments in Galician white grapevine cultivars?

摘要

Aims: To evaluate the usefulness of predawn water potential (Ψpd) to assess the water status of Galician grapevine cultivars for irrigation purposes.Methods and results: Three Galician white grapevine cultivars (Albari?o, Godello and Treixadura) were subjected to rain-fed and irrigation conditions during the 2013 growing season. Diurnal changes in leaf water potential (Ψl) were measured using a pressure chamber on days with high evapotranspiration demand. Stem water potential (Ψs) was measured at midday. Ψpd was not able to discriminate between treatments, whereas Ψl and Ψs at midday were able to detect significant differences in water status among plants.Conclusion: Ψpd was not useful to evaluate vine water status under the Galician climatic conditions. In contrast, both Ψl and Ψs were effective for detecting differences between treatments and can thus be used for irrigation management purposes.Significance and impact of the study: This is the first study evaluating water status of Galician grapevine cultivars. It also provides useful information about the strategy for its control through measurements of midday Ψl or Ψs. IntroductionEstimating crop water status is usually based on plant responses to water stress, mainly leaf water potential measured at predawn (Ψpd) or leaf (Ψl) and stem (Ψs) water potentials at midday (Choné et al., 2000). These measurements can be used for irrigation management since they are good predictors of plant performance under different irrigation regimes (Shackel, 2007).In Galicia (NW Spain), the changing climate conditions and the lack of research on grapevine water needs have raised the interest in understanding the physiological and agronomical response of Galician cultivars to irrigation, which is increasingly being used in Galicia (Mirás-Avalos et al., 2013). In this context, studies on the water relations of Galician grapevine cultivars are needed in order to provide tools for an efficient irrigation management.Therefore, the aim of this work was to evaluate the use of Ψpd and Ψl for assessing the water status of three Galician white grapevine (Vitis vinifera L.) cultivars (Albari?o, Godello and Treixadura), discussing their usefulness for irrigation management.Materials and methods1. Description of the study siteThe experiment was carried out during 2013 in 0.2-ha plots at the experimental farm of the Estación de Viticultura e Enoloxía de Galicia (EVEGA) in Leiro (Ourense, NW Spain) within the Ribeiro Designation of Origin (42o 21.62’ N, 8o 7.02 W, 110 m above mean sea level).Soil at the site is sandy-textured with 69% sand, 14% silt and 17% clay, pH (H2O) 6.4 and 2.7% organic matter.According to data recorded at a weather station located within the experimental farm (200 m away from the studied orchards), the average temperature was 17.9 oC and total rainfall was 269 mm for the period from April to September 2013.The studied vineyards were planted with Albari?o, Godello and Treixadura grapevine cultivars, native from Galicia. Plants were 15 years old, grafted onto rootstock 196-17C and vertically shoot-positioned in a single cordon with 10-12 buds per plant. Spacings were 2.4 m x 1.25 m (3,333 plants ha-1).Two treatments were considered for this study: rain-fed and drip irrigation to 50% of potential evapotranspiration (ETo), using two emitters (4 l h-1) per plant, located at 25 cm on each side of the trunk. The experiment was laid out in randomised blocks with three replications. The irrigation period lasted from 17th June to 25th August, which is the period of the highest evapotranspiration demand. In the end, the total water amount supplied to the irrigation treatment was 80 mm.2. DeterminationsData on maximum and minimum air temperatures, relative humidity, wind speed and solar radiation were collected at an on-site weather station.Ψl was measured using a pressure chamber (Pump-Up, PMS Instruments, OR, USA) at 1-hour intervals starting early in the morning (06:00 am) on two uncovered, mature fully expanded leaves of two randomly selected plants in each replication.Ψs was measured at noon on non-transpiring leaves that had been bagged with both plastic sheet and aluminium foil for at least 1 hour before measurements (Choné et al., 2000).Stomatal conductance was measured on the same leaves as those used for Ψl using a leaf porometer (Model SC1 Decagon Devices, WA, USA). Only one measurement per leaf was taken, prior to the water potential reading.Determinations were carried out on four dates when irrigation was already established, in order to detect differences between treatments: on 18th July and 13th August for Godello, on 23rd July for Albari?o and on 8th August for Treixadura.3. Statistical analysisOne-way analysis of variance was used to determine significant differences between treatments. Linear regression analyses were used for relating water potential measurements to weather data.ResultsOn the measurement days, maximum temperatures were registered early in t