Water relations and photosynthesis as criteria for adequate irrigation management in 'Tahiti' lime trees

Irrigation scheduling based on soil moisture status is one of the most useful methods because of its practicality and low cost. The effects of available soil water depletion on evapotranspiration (ETc), transpiration (E), leaf water potential at predawn (psiP) and midday (psiM), stomatal conductance (gs) and net CO2 assimilation (A) in lime 'Tahiti' trees (Citrus latifolia) were evaluated to improve irrigation schedule and minimize water use without causing water stress. The trees were spaced 7 <FONT FACE=Symbol>&acute;</FONT> 4 m and drip-irrigated by four drippers with the available soil water content (AWC) depleted by suspension of irrigation (40 days). Leaf water potential was measured on a pressure chamber (psiP and psiM) and leaf gas exchange was measured by infrared gas analyzer (E, gs and A). Evapotranspiration was determined with the aid of weighing lysimeter. Water soil content and potential (psiS) were monitored with TDR probes and tensiometers, respectively, installed at 0.3, 0.6 and 0.9 m depths. Meteorological variables were monitored with an automatic weather station in the experimental area. The threshold AWC level for the onset of ETc decline was 43%, and 60% for gs, A, E and Y P. Also, psiP was more sensitive to AWC than psiM, and is therefore a better tool for irrigation. When AWC was around 60%, values of psiP and psis were -0.62 MPa and -48.8 kPa, respectively

Night-time responses to water supply in grapevines (Vitis vinifera L.) under deficit irrigation and partial root-zone drying

Night-time water uptake (S-n) mainly corresponds to stem and organ rehydration and transpiration, the latter through stomata and cuticle. Nocturnal transpiration is uncoupled from photosynthesis, therefore it contributes to reduce water use efficiency (WUE). Night-time grapevine physiology was measured on field grown grapevines (cv. Shiraz) under partial root-zone drying (PRD) and deficit irrigation (Exp. 1), on potted vines (cv. Tempranillo) (Exp. 2) and on potted vines (cv. Cabernet Sauvignon) on a progressive drought treatment in the glasshouse (Exp. 3). Sap flow probes using the compensated heat pulse method (cHP) were installed in vines (Exp. 1 and 3). Night-time gas exchange measurements were performed for Exp. 3. Other vine water status monitoring methods used were: midday stem water potential (Psi(s)) for all experiments, and abscisic acid (ABA) concentration monitored from leaf sap for Exp. 3. Results showed that Sr, was parabolically correlated to Psi(s) measured on the previous day for all treatments and cultivars. Two distinct zones where vines exhibit different night-time behaviour within the Psi(s) vs S-n parabolic relationships were identified for all experiments. The differences between the two identified areas were related to the water status conditions of the vines: (i) non-water stress conditions (0 < Psi(s) < -1.0 MPa); (ii) water stress conditions (-1.0 MPa < Psi(s) < -2.0 MPa). Furthermore, levels of water stress were negatively correlated to concentrations of leaf sap ABA, which helped to explain the parabolic curve found for cv. Cabernet Sauvignon. (C) 2014 Elsevier B.V. All rights reserved