Indicator Of Water Status Research Articles

Interpreting trunk diameter changes in young lemon trees under deficit irrigation

Measurements obtained by the continuous monitoring of sap flow and parameters derived from trunk diameter fluctuations were compared with discrete measurements of conventional plant water status indicators in potted young lemon trees ( Citrus limon (l.) Burm. fil, cv. Verna) grafted on sour orange ( C. aurantium L.) rootstock submitted to high frequency deficit irrigation. The first detectable response to the deficit irrigation was a marked increase in maximum daily trunk diameter shrinkage (MDS) followed by a decrease in sap flow (SF), predawn leaf water potential and leaf conductance values. Daily maximum (MXTD) and minimum (MNTD) trunk diameters were directly influenced by the plant water supply from the soil. When the water stress increased in severity and the trunk growth rate increased, the MDS values in treated plants decreased to reach values similar to those of control plants. Thus, during the first days of deficit irrigation, when trunk growth was very low, MDS and SF served as the best plant water status indicators. Further, when water stress was more pronounced and trunk growth was greater, MNTD, MXTD and SF were the most reliable indicators.

Leaf and stem water potential as vine water status indicators, in Tempranillo grapevine, under different water regimes in the Duero valley

<p style="text-align: justify;">Attempts have been made to determine the water status of vineyards using different methods, with variable results according to the different authors. Therefore, various methods have been used to estimate soil humidity (TDR, tensiometer, neutron probe, etc.) and the water status of the plant (dendrometer, porometer, leaf water potential, xylem water potential, etc.). The leaf water potential measured with leaf and «bagged» leaf, which are subjected to comparison in this report, are two useful and simple methods for finding out the water status of the vines, based on the use of a simple instrument that is acceptably available in economic terms, the pressure chamber.</p><p style="text-align: justify;">The trial was performed at an experimental Tempranillo vineyard in which the main source of variation was the watering regime (no irrigation, 20 % ETo irrigation, 40 % ETo irrigation) and in which a change in planting density was also included (low, 2.7x1.4 m; high, 2.2x1.5 m). The resulting experimental treatments were: B00 (low density and no irrigation), B20 (low density and 20%ETo), H20 (high density and 20%ETo) and H40 (high density and 40 % ETo). The total amount of water applied to the treatments with the lesser irrigation rate (0.2 ETo mm) was equal to 61 mm and to the treatment with the higher irrigation rate (0.4 ETo mm) was equal to 122 mm, up to the week of August 29, 2002. The measurements of Yf were performed before dawn (aa) on June 14, at solar noon (12:00 p.m.) on July 19 and 26 and on August 29, 2002, on adult leaves located in the middle zone of the shoot, above the height of the clusters, on the eastern face of the trellised vines. Yx was measured at 6:00 a.m. on June 14 and at solar noon (12:00 p.m.) on July 19 and 26 and on August 29, 2002, also on adult leaves in the middle zone of the shoot, above the zone of the clusters, leaves located on the western face of the trellised vines and therefore shaded, and covered at least one hour prior to taking the measurement.</p><p style="text-align: justify;">The relationship between the water potential of the leaf and that of the «bagged» leaf has proven to draw closer as the cycle has advanced and the vines have been more stressed, in such a way that the best relationship between the two indicators was obtained in the measurement performed at the end of the month of August. When the water differences are very notable, both indicators are able to show the water status of the vineyard expected in accordance with the rate of irrigation applied.</p><p style="text-align: justify;">The measurement of water potential of the leaf has been easier to take, because it is not necessary to cover the leaves prior to taking the measurement (except in the measurement before dawn, in which case one must be in the vineyard at an unpleasant hour). However, using the potential of the xylem it has been possible to make better observations of the differences between treatments, when these differences are not very important.</p>

De novo protein synthesis in relation to ammonia and proline accumulation in water stressed white clover.

The kinetics of protein incorporation from newly-absorbed nitrogen (N, de novo protein synthesis) was estimated by 15N tracing in 18-week-old white clover plants (Trifolium repens L. cv. Regal) during 7 d of water-deficit treatment. The physiological relationship between kinetics and accumulation of proline and ammonia in response to the change in leaf-water parameters was also assessed. All leaf-water parameters measured decreased gradually under water deficit. Leaf and root dry mass was not significantly affected during the first 3 d when decreases in leaf-water parameters were substantial. However, metabolic parameters such as total N, proline and ammonia were significantly affected within 1 d of commencement of water-deficit treatment. Water-deficit treatment significantly increased the proline and NH3-NH4+ concentrations in both leaves and roots. There was a marked reduction in the amount of N incorporated into the protein fraction from the newly absorbed N (NANP) in water-deficit stressed plants, particularly in leaf tissue. This reduction in NANP was strongly associated with an increased concentration of NH3-NH4+ in roots (P≤0.05) and proline (P≤0.01) in leaves and roots. These results suggest that proline accumulation may be a sensitive biochemical indicator of plant water status and of the dynamics of de novo protein synthesis in response to stress severity.

Phytomonitoring in Kiwifruit orchards as a plant water status indicator and its use in irrigation scheduling.

This article describes the use of phytomonitoring equipment in kiwifruit orchards in Chile. Plant growth and fruit development responses to water stress strategies are analyzed, with actual data obtained from a phytomonitor installed within a commercial orchard. Continuous monitoring of trunk, cane and fruit diameter, leaf temperature, stem sap flow velocity, soil moisture and microclimatic data (incident radiation, air temperature, wind conditions and relative air humidity) are made possible by using phytomonitoring sensors and special software. Phytomonitor Information is compared with data obtained from a conventional automatic weather station, soil tensiometers and neutron moisture probes. Normal and deficit irrigation periods are evaluated, concluding that the use of phytomonitoring techniques in irrigation management represent a significant and comprehensive breakthrough in the evaluation of plant responses to soil water availability. Este trabajo describe el uso de equipos de fitomonitoreo en un huerto de kiwi en Chile. El crecimiento vegetativo y el desarrollo de los frutos en respuesta a estrategias de riego deficitario, se analizan con datos recolectados por una bateria de sensores instalados en el interior de una plantacion comercial. Estos sensores permiten la medicion continua del diametro de troncos, brotes y frutos, asi como la temperatura foliar, el flujo de savia en el tronco, el contenido de agua en el suelo y datos microclimaticos (radiacion incidente, temperatura y humedad relativa del aire, e intensidad y direccion del viento. La informacion recolectada por los sensores es procesada con un sistema computacional especialmente disenado con este proposito. La informacion obtenida con el fitomonitor se compara con informacion obtenida de una estacion meteorologica automatica convencional, tensiometros y neutrometro de humedad del suelo. Se evaluan periodos de riego normal, alternados con eventos de riego deficitario, concluyendose que el uso de las tecnicas de fitomonitoreo para la programacion del riego representan un avance tecnologico significativo en la evaluacion de las respuestas de las plantas a las condiciones de disponibilidad hidrica.

Thermal dehydration-induced thirst in lithium-treated rats

Lithium is used as the primary treatment for bipolar disorder but has the common side effects of diuresis and thirst. In the present study, the effects of lithium on water balance responses of male Sprague–Dawley rats to thermal dehydration were examined. Rats ate either unadulterated food or food containing 2 g/kg lithium carbonate for 10 days. Then the control and lithium-treated rats were exposed to either 25 or 37.5 °C without food or water for 4 h. The rats were then allowed access to water for 3 h at 25 °C or were anesthetized and blood samples were taken. Lithium treatment caused an initial decrease in food intake, a decrease in body weight, and an increase in urine output. Heat exposure caused similar increases in evaporative water loss in control and lithium-treated rats. Heat exposure led to changes in blood indicators of body water status indicative of dehydration, whereas lithium had no effects on blood indicators of body water status. Water intake was increased by both heat exposure and by lithium treatment with the lithium-treated rats being more responsive to the thirst-inducing effects of thermal dehydration. Lithium treatment does not appear to impair water balance responses to heat exposure.

Comparison of water status indicators for young peach trees

We measured a series of physiological and physical indicators and compared them to xylem sap flow, to identify the most sensitive and reliable plant water status indicator. In the growing season of 1998, 4-year-old peach trees (Prunus persica Batsch cv. 'Suncrest', grafted on 'GF 677' rootstock) were studied under two irrigation treatments, 25 l day−1 and no irrigation, and during recovery. Trials were conducted near Pisa (Italy) in a peach orchard situated on a medium clay loam soil and equipped with a drip-irrigation system (four 4 l h−1 drippers per tree). Measurements of leaf water potential (Ψ W ), stem water potential (Ψ S ), and leaf temperature (T l) were taken over 5 days (from dawn to sunset) and analyzed in conjunction with climatic data, sap flow (SF), trunk diameter fluctuation (TDF) and soil water content (SWC). Physiological indicators showed substantial differences in sensitivity. The first indication of changes in water status was the decrease of stem radial growth. TDF and SF revealed significant differences between the two irrigation treatments even in the absence of differences in pre-dawn leaf water potential (pdΨW), up until now widely accepted as the benchmark of water status indicators. Irrigated trees showed a typical trend in SF rate during the day, while in non-irrigated plants the maximum peak of transpiration was anticipated. Measurements of water potential showed ΨS to be a better indicator of tree water status than ΨW. T l was found to have poor sensitivity. In conclusion, we found the sensitivity of the indicators from the most to the least was: TDF >SF rate >SF cumulated = pdΨW=ΨS>mdΨW>T l.

Spectral absorption features as indicators of water status in coast live oak ( Quercus agrifolia ) leaves

A total of 139 reflectance spectra (between 350 and 2500 nm) from coast live oak ( Quercus agrifolia ) leaves were measured in the laboratory with a spectrometer FieldSpec®Pro FR. Correlation analysis was conducted between absorption features, three-band ratio indices derived from the spectra and corresponding relative water content (RWC, %) of oak leaves. The experimental results indicate that there exist linear relationships between the RWC of oak leaves and absorption feature parameters: wavelength position (WAVE), absorption feature depth (DEP), width (WID) and the multiplication of DEP and WID (AREA) at the 975 nm, 1200 nm and 1750 nm positions and two three-band ratio indices: RATIO 975 and RATIO 1200, derived at 975 nm and 1200 nm. AREA has a higher and more stable correlation with RWC compared to other features. It is worthy of noting that the two three-band ratio indices, RATIO 975 and RATIO 1200, may have potential application in assessing water status in vegetation.

The assessment of vine water and nitrogen uptake by means of physiological indicators influence on vine development and berry potential (<em>Vitis vinifera</em> L. cv Merlot, 2000, Bordeaux)

<p style="text-align: justify;">Vine water and nitrogen uptake can be assessed by means of physiological indicators in field conditions. In this study, pre-dawn leaf water potential (ψB) and stem water potential (ψT) were used to indicate vine water status of <em>Vitis vinifera</em> L cv. Merlot. Carbon isotope composition of grape sugar (ΔC13) was used as an integrative indicator of vine water deficit during the ripening period. Must assimilable nitrogen and leaf blade colour intensity, were used to assess vine nitrogen status. All of the three indicators of vine water status allowed a clear differentiation of vine water uptake conditions in the ten experimental plots. The indicators of vine nitrogen status showed more ambiguous results. Must assimilable nitrogen content did not only vary with vine nitrogen uptake, but also with yield. Leaf colour was more easy to interpret. Vine development and berry composition were more influenced by water uptake conditions than by vine nitrogen status. In 2000, which was a dry vintage in Bordeaux, water stress induced early growth slackening and a small berry size. Grapes contained more sugar, anthocyanin and total phenolics and less malic acid when water availability was low. On plots where water uptake conditions were similar, low vine nitrogen status increased berry potential.</p>

Using the CERES-Maize model in a semi-arid Mediterranean environment. New modelling of leaf area and water stress functions

The CERES-Maize model does not simulate satisfactorily the productivity under soil water scarcity. In a previous paper by Ben Nouna et al. (Eur. J. Agron. 13 (2000) 309), this poor performance was attributed to an inaccurate leaf surface simulation and to the water stress function. This paper proposes the introduction of two new modules in the original version of CERES-Maize model. For the LAI module, an analytical approach is followed, consisting of simulating the leaf area of each individual leaf, by the calibration of different functions (leaf appearance, leaf area growth, end of leaf growth, leaf senescence). The new stress function expresses the ratio of actual to maximum evapotranspiration rate as a function of an indicator of the plant water status (pre-dawn leaf water potential). The two modules have been separately introduced into the CERES model and the output compared with the observed values and those simulated by the CERES model in its original version. The results of validation showed that the revised LAI module improved the LAI prediction compared with the one of the original model. Moreover, for the purpose of generalising the new LAI module, its predictions were also compared with the LAI simulated by the Muchow et al. model (Agron. J. 87 (1990) 338), which has been calibrated at several latitudes with different maize varieties. As compared with the original version of CERES, the new water stress function gave a different prediction in terms of the timing and intensity of soil water deficit during the cropping cycle. The stress intensity, as calculated by the new function, was generally less severe than that simulated by the original version.

Carbon isotope composition of sugars in grapevine, an integrated indicator of vineyard water status.

Photosynthetic carbon isotope composition (delta(13)C) was measured on sugars in mature fruits from field-grown grapevines. Sugar delta(13)C and summer predawn leaf water potential were significantly correlated. The survey of different vineyards during four growing seasons showed that sugar delta(13)C in must at harvest varied from -20 per thousand to -26 per thousand when conditions during berry maturation varied from dry to wet. This range allows a very sensitive detection of grapevine water status under natural conditions. However, local differences due to soil capacity to supply water to grapevines are maintained, whatever the annual water balance. Leaf nitrogen content variations of field-grown grapevines did not change delta(13)C values. Genetic variability of delta(13)C between 31 grapevine varieties for delta(13)C was observed. Must sugar delta(13)C can be used to characterize vineyards for their soil structural capacity to provide water to grapevines. It was concluded that isotope carbon composition in grapevine measured on sugars at harvest can be applied to compare the capacities of vineyard soils and canopy management to induce mild water stress in order to produce premium wines.

Plant indicators for scheduling irrigation of young olive trees

The sensitivity of several water status indicators was determined in irrigated young olive trees subjected to two drought periods at Cordoba, Spain. Trunk diameter fluctuations (TDF) were monitored continuously and stem water potential (ψ), leaf photosynthesis (P n) and conductance (g l) were measured periodically on trees where irrigation was interrupted or which were fully irrigated. During the first period of water deprivation in late spring, only some of the TDF-derived parameters were able to detect significant differences caused by water deficits, while there were no differences in stem ψ, P n and g l. All water stress indicators responded during the second drought period in midsummer. However, differences in maximum trunk diameter were detected several days before significant stem ψ differences of about 0.2 MPa were established between treatments. Stem ψ differences declined further to 0.6 MPa before differences in leaf P n and g l became significant. Of all TDF-derived indices, trunk growth rate was the most sensitive to water deficits while treatment differences in maximum daily shrinkage were insignificant in the young trees. It is concluded that continuous monitoring of trunk diameter provides the most sensitive indicator for accurate, automated irrigation scheduling of young olive trees under intensive production.

Evapotranspiration of sweet sorghum: A general model and multilocal validity in semiarid environmental conditions

A model of canopy resistance rc is presented for the determination of actual crop evapotranspiration using the Penman‐Monteith type of model at hourly and daily scales. Here rc is deduced from weather variables (net radiation, air temperature and humidity, and wind speed) and by an indicator of the crop water status measured on the plants: the predawn leaf water potential (i.e., measured before dawn). The model needs a calibration “per crop” and not “per site”; that is, once it is calibrated for a given crop in a certain locality, then it can be used anywhere without further calibration. The model was tested on sorghum crops in different water conditions at two sites in southern Italy for several years. The results showed that it performs well at hourly, daily, and seasonal scales. In fact, the difference between the cumulative values of the actual evapotranspiration measured and the one calculated by the model ranges between −9% and +11%. We concluded that it is not sensitive to climate and soil type or to crop species and variety.

Diurnal changes in branch diameter as indicator of water status of Hinoki cypress Chamaecyparis obtusa

We investigated use of strain gauges for monitoring the water status of trees by measuring changes in the diameter of the largest spreading branch of a 27-year-old Chamaecyparis obtusa tree. The change in xylem diameter in the branch is more closely related than the change in phloem diameter to the change in leaf water potential. Since the diurnal changes in diameter match the diurnal changes in water balance (sap flow velocity – transpiration), measuring the change in xylem diameter using a strain gauge is useful in evaluating the water status of C. obtusa.

Visual soil water status indicator for improved irrigation management

A device to aid in irrigation scheduling by visually indicating current soil water status relative to an upper and lower set point was developed and field tested. The device can be used by farm managers to easily evaluate current soil water status from a distance. This information can be used to guide irrigation scheduling decisions throughout the season. Seven farm managers evaluated the device on seven commercial potato fields. Two study fields, one with and one without soil water status indicators, were established with each farm manager. Water application was measured in each field. Collectively, farm managers applied 7% (2.9 cm) less water to fields with the soil water status indicators than comparison fields. Average water application was significantly less ( P=0.04) for fields with soil water status indicators. The basic elements of the soil water status indicator and its operation are presented.

Stem Water Potential is a Sensitive Indicator of Grapevine Water Status

Dawn leaf water potential (dawnΨ), leaf water potential (leafΨ) and stem water potential (stemΨ) were measured on mature leaves to determine non-irrigated vine water status in vineyards during the growing season. StemΨ was the most discriminating indicator for both moderate and severe water deficits. The difference between stemΨ and leafΨ (ΔΨ) provided an indirect measurement of mean leaf transpiration which varied with soil moisture conditions and vapour pressure deficit in the atmosphere. The use of stemΨ as an indicator for grapevine management in both non-irrigated and irrigated vineyards is discussed.

Rapid Equilibration of Leaf and Stem Water Potential under Field Conditions in Almonds, Walnuts, and Prunes

Covering a plant leaf with a reflective, water impervious bag ensures that equilibrium is reached between the nontranspiring leaf and the stem, and appears to improve the accuracy of determining plant water status under field conditions. However, the inconvenience of covering the leaf for 1 to 2 hours before measuring stem water potential (SWP) has constrained on-farm adoption of this irrigation management technique. A second constraint has been that the requirement of midafternoon determinations limits the area that can be monitored by one person with a pressure chamber. This paper reports findings from field studies in almonds (Prunus dulcis),prunes (P. domestica), and walnuts (Juglans regia) demonstrating modified procedures to measure midday SWP, making it a more convenient and practical tool for irrigation management. For routine monitoring and irrigation scheduling, an equilibration period of 10 min or longer appears to be suitable to provide accurate SWP measurements. Based on the large sample sizes in this study, we estimate that measurement error related to equilibration time for SWP can be reduced to an acceptable level [0.05 MPa (0.5 bar)] with a sample size of about 10 leaves when using a 10-min equilibration period. Under orchard conditions where tree growth and health appears uniform, a sample of one leaf per tree and 10 trees per irrigation management unit should give an accurate mean indicator of orchard water status. Under more variable orchard conditions a larger sample size may be needed. Midmorning and midday SWP both exhibited similar seasonal patterns and responded alike to irrigation events. On some occasions, midday SWP was accurately predicted from midmorning SWP and the change in air vapor pressure deficit (VPD) from midmorning to midday, but both over- and underestimate errors [to 0.3 MPa (3.0 bar)] appeared to be associated with unusually low or high diurnal changes in VPD, respectively. Hence, direct measurement of SWP under midday conditions (about 1300 to 1500 hr) is still recommended.

Steady-State and Maximum Chlorophyll Fluorescence Responses to Water Stress in Grapevine Leaves: A New Remote Sensing System

A new fluorimeter built at Orsay allowed us to measure at a distance of up to 6 m both the steady-state and the maximum chlorophyll fluorescence. This instrument has been applied continuously during 17 days of water stress development to follow the chlorophyll fluorescence parameters of a potted grapevine. Gas-exchange rates for H 2O and CO 2 and chlorophyll fluorescence parameters of the same leaf were recorded concurrently. It was shown that: (1) Under well-watered conditions, before noon, a correlation was found between net photosynthetic rate and the rate of electron transport calculated from fluorescence measurements. After several hours of high light exposure, CO 2 assimilation (A) started to decrease more than the rate of electron transport (ETR). Under drought conditions, the above-mentioned correspondence was lost: when A almost vanished due to high stomatal closure, the ETR was still about 50% of the control value. It is suggested that under these conditions, the ratio of photorespiration to CO 2 assimilation increased. (2) Light response of the quantum yield of ETR became increasingly different between morning and afternoon as water stress progressed, thus serving as a good indicator of plant water status. (3) A simple fluorescence parameter, Fs, accurately reflected the plant physiological state. Over the range of light intensities used in this study, this parameter changed in parallel with irradiance in well-watered plants. With increasing water stress, Fs changed in opposite direction to irradiance changes. The response of Fs to rapid changes in irradiance was fast (within seconds). The potential of this parameter for remote sensing of water stress is discussed.

Shoot growth on de-fruited grapevines: a physiological indicator for irrigation scheduling

A simple and inexpensive but biologically meaningful way of gauging grapevine water status that can guide irrigation scheduling is described. The growth rate of shoots on grapevines from which all fruit has been removed (de-fruited shoot growth) is presented as a sensitive indicator of vine and soil water status and we propose a procedure for irrigation scheduling based on monitoring de-fruited shoot growth and soil moisture. These guidelines were derived from corresponding measurements of de-fruited shoot growth and soil moisture potential that were undertaken at frequent intervals (generally 1 to 2 days). De-fruited shoot growth rate between 48 and 71 days after anthesis was linearly correlated with the mean moisture potential of the soil at depths of 60 cm and 90 cm in the centre of the drip-irrigated zone (r = 0.94). De-fruited shoot growth effectively ceased when soil moisture potential at these points had decreased to -70 kPa, although much of the root zone would have been even drier. De-fruited shoot growth thus shows an integrated and dynamic response to vine-available soil water that could aid irrigation scheduling.

Sap flow index as an indicator of plant water status

Sap flow index as an indicator of plant water status

Sap flow index as an indicator of plant water status.

Night and especially predawn tree water status is an important indicator of drought stress in trees. Leaf water potential (LWP) is frequently used as a measure of tree water status and hence drought stress; however, there are difficulties associated with sampling foliage from tall trees and determining LWP automatically. The current study was undertaken to determine whether sap flow index (SFI), which can be automatically and continuously recorded even during very low flows, can be used to estimate drought stress in trees caused by dry air under non-limiting soil water conditions. We made simultaneous measurements of LWP, heat pulse velocity (HPV) and SFI on apple trees (Malus domestica Borkh.) in the semiarid climate of southern Ukraine over several growing seasons. Predawn values of LWP were highly correlated with SFI. Over the range of low sap flow rates occurring at nighttime, where other methods of measuring sap flow are not sensitive, the SFI method was linear and very sensitive. Additional information about tree water status was obtained by comparing nighttime and daytime values of SFI. The ratio of predawn SFI to midday SFI and the period between the two daily SFI maxima (the first SFI peak occurred in the morning and the second peak occurred in the evening on cloudless days) can be used to characterize internal plant water balance. Although the daily course of SFI was variable, specific patterns were identified that reflected particular stages in the development of plant drought stress. An "air-drought-stress curve" was used to characterize the development of water stress in trees subjected to air drought during the growing season.