Estimate Water Potential Research Articles

Spectral ecophysiology: hyperspectral pressure-volume curves to estimate leaf turgor loss.

Turgor loss point (TLP) is an important proxy for plant drought tolerance, species habitat suitability, and drought-induced plant mortality risk. Thus, TLP serves as a critical tool for evaluating climate change impacts on plants, making it imperative to develop high-throughput and in situ methods to measure TLP. We developed hyperspectral pressure-volume curves (PV curves) to estimate TLP using leaf spectral reflectance. We used partial least square regression models to estimate water potential (Ψ) and relative water content (RWC) for two species, Frangula caroliniana and Magnolia grandiflora. RWC and Ψ's model for each species had R2 ≥ 0.7 and %RMSE = 7-10. We constructed PV curves with model estimates and compared the accuracy of directly measured and spectra-predicted TLP. Our findings indicate that leaf spectral measurements are an alternative method for estimating TLP. F. caroliniana TLP's values were -1.62 ± 0.15 (means ± SD) and -1.62 ± 0.34 MPa for observed and reflectance predicted, respectively (P > 0.05), while M. grandiflora were -1.78 ± 0.34 and -1.66 ± 0.41 MPa (P > 0.05). The estimation of TLP through leaf reflectance-based PV curves opens a broad range of possibilities for future research aimed at understanding and monitoring plant water relations on a large scale with spectral ecophysiology.

Evaluating the Applicability of Thermal Infrared Remote Sensing in Estimating Water Potential of the Karst Aquifer: A Case Study in North Adriatic, Croatia

One of the most prominent tourist destinations in the Adriatic coast, the city of Opatija, is facing a problem concerning seasonal drinking water shortages. The existing water resources are no longer sufficient, and attention is being given to alternative resources such as the underlying karstic aquifer and several coastal springs in the city itself. However, the water potential of the area still cannot be estimated due to the insufficient hydrological data. The goal of this research was to evaluate the use of thermal infrared (TIR) remote sensing as the source of valuable information that will improve our understanding of the groundwater discharge dynamics. Ten Landsat ETM+ (enhanced thematic mapper plus) and two Landsat TM (thematic mapper) images of the north Adriatic, recorded during 1999–2004 at the same time as the field discharge measurements, were used to derive sea surface temperature (SST) and to analyze freshwater outflows seen as the thermal anomaly in the TIR images. The approach is based on finding the functional relationship between the size of the freshwater thermal signatures and the measured discharge data, and to estimate the water potential of the underlying aquifer. It also involved analyzing the possible connection between the adjusted size of the spring’s thermal signatures and groundwater level fluctuations in the deeper karst hinterland. The proposed methodology resulted in realistic discharge estimates, as well as a good fit between thermal anomalies with measured discharges and the groundwater level. It should be emphasized that the results are site specific and based on a limited data set. However, they confirm that the proposed method can provide additional information on groundwater outflow dynamics and coastal springs’ freshwater quantification.

Vineyard water status estimation using multispectral imagery from an UAV platform and machine learning algorithms for irrigation scheduling management

Remote sensing can provide a fast and reliable alternative for traditional in situ water status measurement in vineyards. Several vegetation indices (VIs) derived from aerial multispectral imagery were tested to estimate midday stem water potential (Ψstem) of grapevines. The experimental trial was carried out in a vineyard in the Shangri-La region, located in Yunnan province in China. Statistical methods and machine learning algorithms were used to evaluate the correlations between Ψstem and VIs. Results by simple regression between VIs individually and Ψstem showed no significant relationships, with coefficient of determination (R2) for linear fitting smaller than 0.3 for almost all the indices studied, except for the Optimal Soil Adjusted Vegetation Index (OSAVI); R2 = 0.42 with statistical significance (p ≤ 0.001). However, results from a model obtained by fitting using Artificial Neural Network (ANN), using all VIs calculated as inputs and real Ψstem from plants within the study site (n = 90) as targets (Model 1), showed high correlation between the estimated water potential through ANN (Ψstem ANN) and the actual measured Ψstem. Training, validation and testing data sets presented individual correlations of R = 0.8, 0.72 and 0.62 respectively. The models obtained from the study site were then applied to a wider area from the vineyard studied and compared to further Ψstem measured obtained from different sites (n = 23) showing high correlation values between Ψstem ANN and real Ψstem (R2 = 0.83; slope = 1; p ≤ 0.001). Finally, a pattern recognition ANN model (Model 2) was developed for irrigation scheduling purposes using the same Ψstem measured in the study site as inputs and with the following thresholds as outputs: Ψstem below −1.2 MPa considered as severe water stress (SS), Ψstem between −0.8 to −1.2 MPa as moderate stress (MS) and Ψstem over −0.8 MPa with no water stress (NS). This model can be applied to analyze on a plant by plant basis to identify sectors of stress within the vineyard for optimal irrigation management and to identify spatial variability within the vineyards.

Micro‐Chilled‐Mirror Hygrometer for Measuring Water Potential in Relatively Dry and Partially Frozen Soils

Estimating water potential in a relatively dry soil is fundamentally important, not only for predicting soil water flows in arid areas or during the evaporation process, but also for understanding soil freezing processes. A micro‐chilled‐mirror hygrometer (FINEDEW) that does not require a sampling chamber and has a rapid response time has recently been developed. The sensor head can be inserted into a soil sample. We confirmed that FINEDEW directly and quickly measures soil water potential in the range of less than −500 kPa in soil under near‐equilibrium conditions and in the range of less than −1000 kPa in soil under evaporation at room temperature. The FINEDEW hygrometer was also applied to frozen soil at temperatures between −20 and −0.5°C. At equilibrium, regardless of soil type and freezing–thawing processes, the measured potential corresponded to the calculated potential determined using the Clausius–Clapeyron equation. Soil water potential was found to require time to reach equilibrium after a temperature change. This is thought to be because ice in the soil pores required time to acquire a new equilibrium geometry.

Non-destructive measurement of grapevine water potential using near infrared spectroscopy

Background and Aims: Near infrared (NIR) spectroscopy techniques are not only used for a variety of physical and chemical analyses in the food industry, but also in remote sensing studies as tools to predict plant water status. In this study, NIR spectroscopy was evaluated as a method to estimate water potential of grapevines. Methods and Results: Cabernet Sauvignon, Chardonnay and Shiraz leaves were scanned using an Integrated Spectronic (300–1100 nm) or an ASD FieldSpec® 3 (Analytical Spectral Devices, Boulder, Colorado, USA) (350– 1850 nm) spectrophotometer and then measured to obtain midday leaf water potential using a pressure chamber. On the same shoot, the leaf adjacent the one used for midday leaf water potential measurement was used to measure midday stem water potential. Calibrations were built and NIR showed good prediction ability (standard error in cross validation (SECV) <0.24 MPa) for stem water potential for each of the three grapevine varieties. The best calibration was obtained for the prediction of stem water potential in Shiraz (R = 0.92 and a SECV = 0.09 MPa). Conclusion: Differences in the NIR spectra were related to the leaf surface from which the spectra were collected, and this had an effect on the accuracy of the calibration results for water potential. We demonstrated that NIR can be used as a simple and rapid method to detect grapevine water status. Significance of the Study: Grapevine water potential can be measured using NIR spectroscopy. The advantages of this new approach are speed and low cost of analysis. It may be possible for NIR to be used as a non-destructive, in-field tool for irrigation scheduling.

Implications of climate change for evaporation from bare soils in a Mediterranean environment

The purpose of this study was to predict quantitative changes in evaporation from bare soils in the Mediterranean climate region of Turkey in response to the projections of a regional climate model developed in Japan (hereafter RCM). Daily RCM data for the estimation of reference evapotranspiration (ETr) and soil evaporation were obtained for the periods of 1994--2003 and 2070--2079. Potential evaporation (Ep) from bare soils was calculated using the Penman-Monteith equation with a surface resistance of zero. Simulation of actual soil evaporation (Ea) was carried out using Aydin model (Aydin et al., Ecological Modelling 182:91-105, 2005) combined with Aydin and Uygur (2006, A model for estimating soil water potential of bare fields. In Proceedings of the 18th International Soil Meeting (ISM) on Soils Sustaining Life on Earth, Managing Soil and Technology, Sanliurfa, 477-480pp.) model of predicting soil water potential at the top surface layer of a bare soil, after performances of Aydin model (R2 = 94.0%) and Aydin and Uygur model (R2 = 97.6) were tested. The latter model is based on the relations among potential soil evaporation, hydraulic diffusivity, and soil wetness, with some simplified assumptions. Input parameters of the model are simple and easily obtainable such as climatic parameters used to compute the potential soil evaporation, average diffusivity for the drying soil, and volumetric water content at field capacity. The combination of Aydin and Aydin and Uygur models appeared to be useful in estimating water potential of soils and Ea from bare soils, with only a few parameters. Unlike ETr and Ep projected to increase by 92 and 69 mm (equivalent to 8.0 and 7.3% increases) due to the elevated evaporative demand of the atmosphere, respectively, Ea from bare soils is projected to reduce by 50 mm (equivalent to a 16.5% decrease) in response to a decrease in rainfall by 46% in the Mediterranean region of Turkey by the 2070s predicted by RCM, and consequently, to decreased soil wetness in the future.

Psychrometric Pressure-Volume Analysis of Osmoregulation in Roots, Shoots, and Whole Sporophytes of Salinized Ceratopteris

Osmotic and turgor adjustment in roots, shoots, and whole sporophytes of a NaCl-tolerant mutant and a NaCl-sensitive wild-type strain of the fern Ceratopteris richardii Brongn. were characterized following exposure to 60 millimolar NaCl, using a psychrometric approach to pressure-volume analysis. Water potential components of whole plants and shoots at full or ambient hydration were similar between strains. Roots of the mutant, however, had osmotic potentials at full turgor and water potentials at zero turgor which were lower (0.32 and 0.46 megapascal, respectively) than those in roots of the wild type after salinization. Although compromised in the absence of NaCl, sporophytes of the mutant strain were larger and much less necrotic in 60 millimolar NaCl after 17 days, compared to the wild type. Root growth in the mutant strain was unaffected by salinization and far exceeded root growth in the wild type. Correlation coefficients of the linear regression and the general consistency and precision of the pressure-volume data demonstrated the feasibility of using PV curves for estimating water potential components of roots. The technique should also provide a means of studying osmoregulation in a variety of other rapidly equilibrating plant tissues.

Measurement of Leaf Water Potential in Wheat with a Pressure Chamber1

AbstractEstimates of leaf water potential obtained with a pressure chamber and with thermocouple psychrometers were compared for wheat (Triticum aestivum L.) leaves at late tillering and early heading stages of growth. The methods were linearly related for both stages of growth, but the equations were different. The pressure chamber required a separate calibration for estimating water potential of leaves from two locations on wheat plants.

Water Potential Gradient in a Tall Sequoiadendron

With an elevator installed in a 90-meter tall Sequoiadendron to collect the samples, xylem pressure potential measurements were made approximately every 15 meters along 60 meters of the tree's height. The measured gradient was about -0.8 bar per 10 meters of height, i.e., less than the hydrostatic gradient. Correction of the xylem pressure potential data by calibration against a thermocouple psychrometer confirmed this result. Similar gradients are described in the literature in tall conifers at times of low transpiration, although a different sampling technique was used. If the data in the present study and those supporting it are typical, they imply a re-evaluation of either the use of the pressure chamber to estimate water potential or the present theories describing water transport in tall trees.

An Apparatus For Measuring Water Potentials in the Xylem of Intact Plants

A new method and apparatus for estimating water potentials in the xylem of intact plants are described. The apparatus is based on the thermocouple psychro-meter method of measuring water potentials, but measurements are made on leaves which remain attached to plants. Illustrative experiments are described, in which continuous records of the estimated water potential in the xylem of cotton and pepper plants are given for periods of up to 10 hr.