Evaluation of a Non-Destructive Method for Measuring Turgor Pressure in Helianthus

The portable instrument described by Heathcote, Etherington,and Woodward (1979) for the non-destructive measurement of turgorpressure was evaluated in Helianthus annuus and Helianthus paradoxus.A good correlation was obtained between turgor pressure measuredwith the instrument and turgor pressure estimated by the pressure-volumetechnique for individual leaves allowed to dry after excision;however, variation in both the intercept and slope of the relationshipoccurred between leaves. Consequently, there was no correlationbetween the output of the instrument for individual leaves andthe turgor pressure of the same leaves estimated by conventionalmethods. Moreover, for a given leaf, the instrument had onlya limited ability to detect temporal variation in turgor pressurewhen compared with turgor pressure calculated from measuredvalues of leaf water potential and leaf osmotic potential. Theinstrument's output was influenced by its proximity to majorveins and by leaf thickness. We conclude that variability inleaf thickness and the presence of large veins limits its usefulnessfor measurement of turgor pressure in Helianthus. Key words: Leaf thickness, Turgormeter, Turgor pressure, Helianthus     

Water Stress and Leaf Growth of Field Beans (Vicia faba L.) in the Field: Water Potentials and Laminar Expansion

Field beans were grown in three different irrigation treatments.The growth of each leaf was followed and estimates made of plantwater potential at dawn and of plant water potential, solutepotential, and pressure potential in the afternoon. The growthin area of the leaves against time was fitted with a logisticcurve from which the parameters of leaf growth were defined.The parameters were the area at which a leaf unfolds, the meangrowth rate, and the duration of growth, which combine to givethe final leaf size. Water stress reduced the final leaf sizeby reducing both the area at unfolding and the mean growth rate.The duration of growth was not consistently altered. Final leafsize was closely correlated with the plant water potential inthe afternoon and apparently more with pressure than solutepotential. Vicia faba, field bean, water stress, leaf area, leaf growth, water potential     

Pressure chamber measurements using two wheat leaves

Summary The most widely used technique of leaf water potential measurements is with the Scholander pressure chamber. Representative leaf water potential values require many determinations on individual leaves and this can be time consuming in large fields or experiments with multiple treatments. This paper describes a method of obtaining a mean value more rapidly, by using two leaves in the pressure chamber at the same time, but recording the end point of each leaf separately.     

Knudsen-transitional flow and gas pressurization in leaves of nelumbo

Pressures in gas spaces of leaves of the lotus Nelumbo are higher than ambient pressure. The pressurization capacity of leaves was studied as a function of leaf temperature, and the composition of air entering evacuated leaves was used to calibrate the pore sizes which determine flow in these leaves. The adaxial side of the leaf of Nelumbo has two distinct regions in terms of gas exchange characteristics. There is a region of relatively high mean pore diameter in the center of the leaf opposite the point of petiole insertion. Gas exchange between the remainder of the leaf (>99% by area) and the atmosphere is restricted by “pores” with an effective mean diameter less than 0.03 micrometer. As a result, a flowthrough ventilation operates within each leaf. Air enters the leaf across the expanse of the lamina, and escapes back to the atmosphere through the highly porous region at the center of the lamina.     

A rapid leaf-disc sampler for psychrometric water potential measurements

An instrument was designed which facilitates faster and more accurate sampling of leaf discs for psychrometric water potential measurements. The instrument consists of an aluminum housing, a spring-loaded plunger, and a modified brass-plated cork borer. The leaf-disc sampler was compared with the conventional method of sampling discs for measurement of leaf water potential with thermocouple psychrometers on a range of plant material including Gossypium hirsutum L., Zea mays L., and Begonia rex-cultorum L. The new sampler permitted a leaf disc to be excised and inserted into the psychrometer sample chamber in less than 7 seconds, which was more than twice as fast as the conventional method. This resulted in more accurate determinations of leaf water potential due to reduced evaporative water losses. The leaf-disc sampler also significantly reduced sample variability between individual measurements. This instrument can be used for many other laboratory and field measurements that necessitate leaf disc sampling.     

Effects of drought on nutrient and ABA transport in Ricinus communis

We studied the effects of variations of water flux through the plant, of diurnal variation of water flux, and of variation of vapour pressure deficit at the leaf on compensation pressure in the Passioura-type pressure chamber, the composition of the xylem sap and leaf conductance in Ricinus communis. The diurnal pattern of compensation pressure showed stress relaxation during the night hours, while stress increased during the day, when water limitation increased. Thus compensation pressure was a good measure of the momentary water status of the root throughout the day and during drought. The bulk soil water content at which predawn compensation pressure and abscisic acid concentration in the xylem sap increased and leaf conductance decreased, was high when the water usage of the plant was high. For all xylem sap constituents analysed, variations in concentrations during the day were larger than changes in mean concentrations with drought. Mean concentrations of phosphate and the pH of the xylem sap declined with drought, while nitrate concentration remained constant. When the measurement leaf was exposed to a different VPD from the rest of the plant, leaf conductance declined by 400mmol m^?2 s^?1 when compensation pressure increased by 1 MPa in all treatments. The compensation pressure needed to keep the shoot turgid, leaf conductance and the abscisic acid concentration in the xylem were linearly related. This was also the case when the highly dynamic development of stress was taken into account.     

An Apparatus for the Measurement of Leaf Dielectric Properties in the High Frequency Region

An instrument is described which permits measurements of a combinationof the dielectric constant and dielectric loss of leaves tobe made over a relatively small area of a leaf. The instrumentreadings have been shown to correlate with the water contentof filter paper, and reasonably well with the water contentof leaf tissue. Results obtained from leaves when their transpirationrate was increased are given.     

A New Porometer Based upon the Electrical Current Produced by Guard Cells

Stomatal guard cells extrude protons when the stomata open.This gives rise to an electrical current which is proportionalto the degree of stomatal opening. An instrument has been developedto measure this leaf surface current which is, in effect, anew type of porometer. The performance of the new porometerhas been compared with that of a commercially available diffusionporometer and a close relationship between leaf surface currentand stomatal conductance was observed for all the species investigated.It is concluded that the instrument has several advantages overthe diffusion porometer, in particular, its small size and simplicityof operation, making it especially suitable for use in the field. Key words: Leaves, stomata, electrical currents, porometry     

A Mechanical Viewing Aid for Microscopical Examination of Convoluted Leaf Surfaces of Forage Grasses

An inexpensive instrument is described which allows all aspectsof the convoluted leaf surfaces of certain forage grasses tobe viewed and measured microscopically, using optic fibres.The instrument fits on a standard microscope stage and allowsup to x40 objectives to be used. Key words: Microscope, Leaf surface, Grasses     

Higher rates of leaf gas exchange are associated with higher leaf hydrodynamic pressure gradients

Steady-state leaf gas-exchange parameters and leaf hydraulic conductance were measured on 10 vascular plant species, grown under high light and well-watered conditions, in order to test for evidence of a departure from hydraulic homeostasis within leaves as hydraulic conductance varied across species. The plants ranged from herbaceous crop plants to mature forest trees. Across species, under standardized environmental conditions (saturating light, well watered), mean steady-state stomatal conductance to water vapour (g(w)) was highly correlated with mean rate of CO2 assimilation (A) and mean leaf hydraulic conductance normalized to leaf area (k(leaf)). The relationship between A and g(w) was well described by a power function, while that between A and k(leaf) was highly linear. Non-linearity in the relationship between g(w) and k(leaf) contributed to an increase in the hydrodynamic (transpiration-induced) water potential drawdown across the leaf (delta psi(leaf)) as k(leaf) increased across species, although across the 10 species the total increase in delta psi(leaf) was slightly more than twofold for an almost 30-fold increase in g(w). Higher rates of leaf gas exchange were therefore associated with higher k(leaf) and higher leaf hydrodynamic pressure gradients. A mechanistic model incorporating the stomatal hydromechanical feedback loop is used to predict the relationship between delta psi(leaf) and k(leaf), and to explore the coordination of stomatal and leaf hydraulic properties in supporting higher rates of leaf gas exchange.     

Use of a model of photosynthesis and leaf microenvironment to predict optimal stomatal conductance and leaf nitrogen partitioning

Abstract. A model of photosynthesis (PGEN) is presented. The model assumes that optimal use is made of the leaf nitrogen available for partitioning between the carboxylase and thylakoid components. This results in predictions of Rubisco and chlorophyll concentrations very similar to those measured elsewhere. A function is incorporated which represents the detrimental effects of negative leaf water potentials on the Calvin cycle, producing a quantitative and mechanistic trade-off between CO2 entering, and H₂O leaving, the leaf. Thus, an optimal stomatal conductance and associated internal partial pressure of CO₂ exists for any given set of environmental conditions. The model calculates this optimal state for the leaf, which is its output. The model was subjected to changes in the following parameters: soil water potential, irradiance, ambient CO2 partial pressure, leaf temperature, leaf-to-air vapour pressure deficit, wind speed, atmospheric pressure, leaf nitrogen content, root dry weight and leaf width. These perturbations resulted in changes in predicted optimal conductance which were very similar to what has been observed. In general, as the capacity of the leaf to fix CO₂ increased, so did the predicted optimal conductance, with the internal partial pressure of CO2 being maintained close to 22Pa.     

A Simple Instrument for Measuring Leaf Extension in Grasses, and its Application in the Study of the Effects of Water Stress on Maize and Sorghum

The design of a simple instrument to monitor leaf expansionin grasses is described. The instrument was used to comparethe effects of water stress on leaf extension of two cultivarsof maize and sorghum. The effect of withholding water for 3days was an appreciable reduction in the rate of leaf expansionin both plants, particularly during the light period. In well-wateredplants of both species, leaf extension continued at a steadyrate even when leaf turgor fell to around 0.1 MPa. In water-stressedmaize plants, leaf turgor during the light period fell to zeroand leaf growth ceased. When turgor was restored, followingstomatal closure, leaf extension resumed at a slow rate. Inunwatered sorghum plants, leaf turgor remained at a value greaterthan 0.1 MPa but the rate of leaf extension was significantlyreduced. The reduction in leaf turgor in the unwanted plantsresulted partly from an increase in solute potential. Zea mays L, maize, Sorghum bicolor L, leaf expansion, leaf turgor, water stress     

Effect of the rol genes from Agrobacterium rhizogenes on polyamine metabolism in tobacco roots

Plants of the mangrove species Pelliciera rhizophoreae and Avicennia germinans, exhibit pronounced oscillations in stomatal aperture under certain climatic conditions. During these oscillations, changes in transpirational water loss were closely followed by those in leaf water potential (ψ1) as indicated by continuous monitoring with an in situ dewpoint hygrometer. With this instrument, it was possible to measure dynamic changes in ψ1 for several days under constant conditions. Subsequently, the leaf was detached from the shoot and a pressure-volume (PV) curve was established by repeatedly weighing the leaf, still attached to the hygrometer during short interruptions of the water potential recordings. The pressure-volume relationship was then used to derive other water relations parameters from these water potential data. Thus, the procedure described herein allows a continuous analysis of the relevant components of bulk leaf water relations. Oscillations in water potential were also measured with single leaves using a pressure chamber. Water relations data obtained with these two different methods were in good agreement. In addition, osmotic potentials derived from the PV-analysis were well within the range of those determined cryoscopically using extracted cell sap.     

The water relations of the root–soil interface

The difference in hydrostatic pressure between the xylem of the leaf and the soil depends, for a given transpiration rate, on the series of hydraulic resistances encountered along this pathway. Many studies have shown that the sum of the resistances in the plant and the soil is too small to account for the fall in water pressure between the leaf xylem and the soil, especially when plants are growing in sandy soils, which are prone to dry rapidly. A resistance at the root–soil interface, caused possibly by poor contact between the roots and the soil, has been proposed to account for the discrepancy. We explored the resistance in the pathway from soil to leaf using a technique that allows precise and continuous non-destructive measurement of the hydrostatic pressure in the leaf xylem. When the soil was leached with water, the fall in leaf water status as the soil dried was reasonably well described by a simple physical model without the need to invoke an interfacial resistance. However, when the soil was flushed with a nutrient solution with an osmotic pressure of 70kPa, the hydrostatic pressure in the leaf xylem fell several times faster than that in the soil. We suggest that solutes accumulated either in the root or just outside it, creating large osmotic pressures, which gave the appearance of an interfacial resistance.     

Morphological changes along an altitude gradient and their consequences for an andean giant rosette plant

Summary Selected morphological features were measured in five populations of the giant rosette plant Espeletia schultzii occurring along an elevation gradient from 2600 to 4200 m in the Venezuelan Andes. Pith volume per amount of leaf area increases with elevation resulting in significantly larger water storage capacity at higher elevations. Thickness of leaf pubescence and, therefore, leaf boundary layer resistance, also increases with elevation resulting in both potentially higher leaf temperatures relative to air temperature and higher leaf to air vapor pressure gradients. The net effect on transpiration rate would depend on ratios of stomatal to boundary layer resistance and leaf energy balance. At higher elevations the central rosette leaves are more vertically oriented and the leaf bases show a pronounced curvature as the intersection with the main axis is approached. This gives these rosettes a distinctly paraboloid appearance and probably enhances capture and retention of incident long and shortwave radiation by the apical bud and expanding leaves. Features which result in enhanced water storage capacity and higher plant temperatures relative to air temperature without greatly increasing water loss are adaptive in high altitude paramo habitats where water availability and growth are limited by year round low temperatures (mean 2–3° C).     

A novel, non-invasive, online-monitoring, versatile and easy plant-based probe for measuring leaf water status

A high-precision pressure probe is described which allows non-invasive online-monitoring of the water relations of intact leaves. Real-time recording of the leaf water status occurred by data transfer to an Internet server. The leaf patch clamp pressure probe measures the attenuated pressure, P(p), of a leaf patch in response to a constant clamp pressure, P(clamp). P(p) is sensed by a miniaturized silicone pressure sensor integrated into the device. The magnitude of P(p) is dictated by the transfer function of the leaf, T(f), which is a function of leaf patch volume and ultimately of cell turgor pressure, P(c), as shown theoretically. The power function T(f)=f(P(c)) theoretically derived was experimentally confirmed by concomitant P(p) and P(c) measurements on intact leaflets of the liana Tetrastigma voinierianum under greenhouse conditions. Simultaneous P(p) recordings on leaflets up to 10 m height above ground demonstrated that changes in T(f) induced by P(c) changes due to changes of microclimate and/or of the irrigation regime were sensitively reflected in corresponding changes of P(p). Analysis of the data show that transpirational water loss during the morning hours was associated with a transient rise in turgor pressure gradients within the leaflets. Subsequent recovery of turgescence during the afternoon was much faster than the preceding transpiration-induced water loss if the plants were well irrigated. Our data show the enormous potential of the leaf patch clamp pressure probe for leaf water studies including unravelling of the hydraulic communication between neighbouring leaves and over long distances within tall plants (trees).     

A thermistor leaf thermometer

An instrument is described which allows measurements of leaf temperature within about 0.3 C. It consists of a special thermistor probe, a small circuit box, and a standard ammeter. The circuit box can easily be fixed to the meter and contains a battery, which passes 0.3 milliampere through the thermistor, and also contains an integrated circuit amplifier, so that the meter reads 20 C full scale deflection, with ranges adjustable in 10 C steps. Calibration experiments show the superiority of the thermistor leaf thermometer to a thermocouple pressed onto a rubber surface with a resilience resembling that of a leaf.     

High-pressure-temperature gradient instrument: use for determining the temperature and pressure limits of bacterial growth.

A pressurized temperature gradient instrument allowed a synoptic determination of the effects of temperature and pressure on the reproduction of bacteria. The instrument consisted of eight pressure vessels housed parallel to each other in an insulated aluminum block in which a linear temperature gradient was supported. For a given experiment, eight pressures between 1 and 1,100 bars were chosen; the linear temperature gradient was established over an interval within -20 to 100 degrees C. Pure cultures and natural populations were studied in liquid or solid medium either in short (ca. 2-cm) culture tubes or in long (76.2-cm) glass capillaries. In the case of a pure culture, experiments with the pressurized temperature gradient instrument determined values of temperature and pressure that bounded its growth. Feasibility experiments with mixed populations of bacteria from water samples from a shallow depth of the sea showed that the instrument may be useful in identifying the extent to which a natural population is adapted to the temperatures and pressures at the locale of origin of the sample. Additional conceived uses of the instrument included synoptic determinations of cell functions other than reproduction and of biochemical activities.     

Antagonistic effects of growing season and autumn temperatures on the timing of leaf coloration in winter deciduous trees

Autumn phenology remains a relatively neglected aspect in climate change research, which hinders an accurate assessment of the global carbon cycle and its sensitivity to climate change. Leaf coloration, a key indicator of the growing season end, is thought to be triggered mainly by high or low temperature and drought. However, how the control of leaf coloration is split between temperature and drought is not known for many species. Moreover, whether growing season and autumn temperatures interact in influencing the timing of leaf coloration is not clear. Here, we revealed major climate drivers of leaf coloration dates and their interactions using 154 phenological datasets for four winter deciduous tree species at 89 stations, and the corresponding daily mean/minimum air temperature and precipitation data across China's temperate zone from 1981 to 2012. Results show that temperature is more decisive than drought in causing leaf coloration, and the growing season mean temperature plays a more important role than the autumn mean minimum temperature. Higher growing season temperature and lower autumn minimum temperature would induce earlier leaf coloration date. Moreover, the mean temperature over the growing season correlates positively with the autumn minimum temperature. This implies that growing season mean temperature may offset the requirement of autumn minimum temperature in triggering leaf coloration. Our findings deepen the understanding of leaf coloration mechanisms in winter deciduous trees and suggest that leaf life‐span control depended on growing season mean temperature and autumn low temperature control and their interaction are major environmental cues. In the context of climate change, whether leaf coloration date advances or is delayed may depend on intensity of the offset effect of growing season temperature on autumn low temperature.     

Structural and Functional Changes in the Leaves of Plants from Steppe Communities as Affected by Aridization of the Eurasian Climate

Morphological and physiological characteristics of leaves from plant species collected in steppe communities in the various climatic zones in Eurasia were compared. The changes in leaf structure correlated with the major climatic factors. The mean thickness of leaves increased with increasing mean temperature of July and decreasing mean precipitation, which corresponded to aridity increase. The increased leaf thickness correlated with an increase in the specific leaf weight. The content of chlorophylls (a + b) in leaves greatly varied with plant habitats, whereas the chlorophyll a/b ratio remained unchanged. The chlorophyll content in leaf tissues had a general tendency to decrease with increasing leaf thickness. The leaf chlorophyll content positively correlated (R ² = 0.77) with the proportion of chlorenchyma in leaf tissues. It is concluded that steppe plants adapt to climate aridization at the structural level by increasing the proportion of protective heterotrophic components of the leaf without changing the functional activity of photosynthetic tissues.