Evaluating the usefulness of continuous leaf turgor pressure measurements for the assessment of Persimmon tree water status

Continuous plant water status monitoring is crucial in order to improve irrigation management. The noninvasive Yara ZIM-probe was assessed for detecting plant water stress in Persimmon trees (Diospyros kaki L.f.). The probe measures the pressure transfer function (Pp) through a patch of an intact leaf, which is inversely correlated with the turgor pressure. This technology was evaluated in two parallel experiments involving either distinct watering regimes or rootstocks with different drought tolerance [Diospyros lotus (L) and Diospyros virginiana (V)]. Concomitant measurements of midday stem water potential (Ψstem) and trunk diameter variations were taken throughout the experiments. Pp was highly correlated with Ψstem. Persimmon leaves exhibited the inversed Pp curve phenomena under water stress, which enabled the association of a particular range of Ψstem to each of the three leaf turgor states defined. Persimmon trees with no sign of initial or total inversion ensured Ψstem above −0.8 MPa, values considered of a well-watered Persimmon tree. Yara ZIM-probe readings as well as Ψstem and trunk diameter variation measurements pointed L as a more sensitive rootstock to drought than V. In conclusion, results showed that the Yara ZIM-probe can be used to continuously monitor water status in Persimmon trees although further research would be needed to ensure their feasibility for scheduling irrigation

Influence of soil water content and atmospheric conditions on leaf water potential in cv. "Touriga Nacional" deep-rooted vineyards

Abstract In this study, the influence of soil and atmosphere conditions on noon and basal leaf water potential of vines ‘‘Touriga Nacional’’ in the Da˜o region submitted to different irrigation treatments is analysed. Both indicators showed to be dependent on environmental conditions at the time of measurement. Leaf water potential at noon of fully watered plants was linearly related with atmospheric conditions, with values registered when vapour pressure deficit (VPD) was higher than approximately 3 kPa being no different from the values registered in stressed plants. Therefore, this indicator cannot be reliably used to distinguish different plant water stress levels when atmospheric conditions induce high evaporative demands. The basal leaf water potential (wb) was also influenced by VPD at the time of measurement for all soil water conditions. In well irrigated plants, it was even possible to establish a baseline that can therefore be used to identify nonwater stressed conditions (wb (MPa) = -0.062–0.0972 VPD (kPa), r2 = 0.78). A good correlation was found between soil humidity and wb. However, more than the average value of the whole thickness of soil monitored, the wb values were dependent on the distribution of soil humidity, with the plants responding to the presence of wet layers

From vineyards to controlled environments in grapevine research: investigating responses to climate change scenarios using fruit-bearing cuttings

21 Pags.- 5 Tabls.- 6 Figs.This paper describes the use of fruit-bearing grapevine hardwood cuttings as a model system for grapevine research, translating some studies that are difficult to execute under field conditions in the vineyards to facilities under controlled conditions. This approach enables to simulate in greenhouses future climate conditions and to investigate putative responses of grapevine to climate change. An updated description of how to grow grapevine fruit-bearing cuttings is made, together with modifications to carry out studies of partial rootzone drying, regulated deficit irrigation studies and symbiosis with arbuscular mycorrhizal fungi. We summarize how extensive has been the use of fruit-bearing cuttings in grapevine research over the years, with special emphasis in those experiments that analyze the effects of factors related to climate change, such as elevated CO2, elevated temperature, water availability and UV-B radiation, on grapevine physiology, production and grape quality. A validation of the model is made, comparing results obtained with fruit-bearing cuttings with those obtained from vineyard-grown plants. We discuss some advantages of growing grapevines under elevated CO2 with an atmosphere depleted in 13C, using this stable isotope (13C) and others (15N, 54Fe or 57Fe, etc.) as tracers for C, N and other nutrient metabolism studies.This work was supported by the European Project INNOVINE Call FP7-KBBE-2011-6, Proposal No. 311775, Spanish Ministry of Economy and Innovation (BFU2011-26989, AGL2011-30386-C02-02 and AGL2014-56075-C2-1-R), and Aragón Government (A03 Research Group).Peer reviewe

The effects of applied water at various fractions of measured evapotranspiration on water relations and vegetative growth of Thompson Seedless grapevines

Vegetative growth and water relations of Thompson Seedless grapevines in response to applied water amounts at various fractions of measured grapevine ETc were quantified. Treatments ranged from no applied water up to 1.4 times the water used by vines growing in a weighing lysimeter. All treatments were irrigated at the same frequency as the vines in the lysimeter (whenever they used 2 mm of water), albeit at their respective fraction. Soil water content and midday leaf water potential (Ψl) were measured routinely in four of the irrigation treatments across years. The amount of water depleted in the soil profile ranged from 190 mm for the 0.2 treatment in 1993 to no water depletion for the 1.4 treatment in 1992. The irrigation treatments significantly affected midday Ψl, total shoot length, leaf area per vine, pruning weights and trunk diameter; as applied water decreased so did vegetative growth. Pruning weights were a linear function of the seasonal, mean midday Ψl across growing seasons. The application of water amounts in excess of evapotranspiration negatively affected vegetative growth some of the years. A companion paper will demonstrate that over-irrigation can negatively affect reproductive growth of this grape cultivar due to excess vegetative growth

A step towards new irrigation scheduling strategies using plant-based measurements and mathematical modelling

Because of the increasing worldwide shortage of freshwater and costs of irrigation, a new plant-based irrigation scheduling method is proposed. In this method, two real-time plant-based measurements (sap flow and stem diameter variations) are used in combination with a mathematical water flow and storage model in order to predict the stem water potential. The amount of required irrigation water is derived from a time integration of the sap flow profile, while the timing of the irrigation is controlled based on a reference value for the predicted stem water potential. This reference value is derived from the relationship between midday values of maximum photosynthesis rates and stem water potential. Since modelling is an important part of the proposed methodology, a thorough mathematical analysis (identifiability analysis) of the model was performed. This analysis showed that an initial (offline) model calibration was needed based on measurements of sap flow, stem diameter variation and stem water potential. Regarding irrigation scheduling, however, only sap flow and stem diameter variation measurements are needed for online simulation and daily model calibration. Model calibration is performed using a moving window of 4 days of past data of stem diameter variations. The research tool STACI (Software Tool for Automatic Control of Irrigation) was used to optimally combine the continuous measurements, the mathematical modelling and the real-time irrigation scheduling. The new methodology was successfully tested in a pilot-scale setup with young potted apple trees (Malus domestica Borkh) and its performance was critically evaluated

Model-assisted evaluation of crop load effects on stem diameter variations and fruit growth in peach

Key message: The paper identifies and quantifies how crop load influences plant physiological variables that determine stem diameter variations to better understand the effect of crop load on drought stress indicators. Stem diameter (D (stem)) variations have extensively been applied in optimisation strategies for plant-based irrigation scheduling in fruit trees. Two D (stem) derived water status indicators, maximum daily shrinkage (MDS) and daily growth rate (DGR), are however influenced by other factors such as crop load, making it difficult to unambiguously use these indicators in practical irrigation applications. Furthermore, crop load influences the growth of individual fruits, because of competition for assimilates. This paper aims to explain the effect of crop load on DGR, MDS and individual fruit growth in peach using a water and carbon transport model that includes simulation of stem diameter variations. This modelling approach enabled to relate differences in crop load to differences in xylem and phloem water potential components. As such, crop load effects on DGR were attributed to effects on the stem phloem turgor pressure. The effect of crop load on MDS could be explained by the plant water status, the phloem carbon concentration and the elasticity of the tissue. The influence on fruit growth could predominantly be explained by the effect on the early fruit growth stages