A Porometer for Laboratory and Field Operation

A porometer is described which is easily and rapidly attachedto plant leaves and appears to be a versatile and sensitiveinstrument for laboratory or field measurement of leaf resistanceto air flow. In the laboratory it can be connected to a normalresistance porometer circuit, and in the field to a sphygrnomanometer.A theoretical relationship has been developed and tested whichenables the conversion of leaf resistance obtained with a sphygmomanometerto that obtained with a normal porometer circuit.     

A Krypton Diffusion Porometer for the Direct Field Measurement of Stomatal Resistance

A stomatal diffusion porometer is described which measures directlythe diffusion of radioactive krypton through amphistomatousleaves. The porometer is relatively small and portable and iseasily used under field conditions. It consists of a miniaturediffusion chamber above an acrylic plastic reservoir which contains1200 cm³ of air enriched with ⁸⁵Kr. Geiger tubes in the diffusionchamber and in the reservoir monitor the relative concentrationsof 85Kr. Krypton is allowed to diffuse from the larger reservoirthrough the leaf into the diffusion chamber and the time forits concentration in relation to that in the reservoir to changebetween two fixed values is recorded. When this time lapse wascalibrated against known resistances a linear relationship,independent of temperature was found. Sources of error are analysedand some experiments are described in which the porometer wasused to measure diurnal changes in stomatal resistance. Resistancesof potted sunflower plants (Helianthus annuus L.) grown in agreenhouse were measured with both the krypton diffusion porometerand a condensation-type porometer and the results were usedto calculate both cuticular and stomatal resistances. Demonstrationof field measurements with the porometer include data from eucalyptustrees {Eucalyptus camaldulensis Dehn) and from an unirrigatedcotton crop {Gossypium hirsutum var. SJ 2) growing under semi-aridconditions. Stomatal conductance of the cotton crop during theopening phase was linearly related to solar radiation.     

A portable steady-state porometer for measuring the carbon dioxide and water vapour exchanges of leaves under natural conditions

A portable porometer is described for measuring the steady-state CO₂ and H₂O exchange rates of leaves under natural conditions. The porometer has an open gas exchange system which monitors the differences in concentrations of CO₂ and H₂O entering and leaving a cuvette which is clamped on or around leaves. The cuvette is designed to maintain ambient air temperature and humidity around the leaf. This instrument may also be used to determine CO₂ response curves in the field. Examples of diurnal courses are presented for attached leaves of different species having high and low rates of CO₂ exchange.     

Developments in Mass Flow Porometry

A ventilated leaf attachment clamp is described with which lateralair flow can be measured separately from through flow. Stomatalconductances are expressed with dimensions: mm s^–1. Basedon parallel measurements with a diffusion porometer the relationbetween mass flow and diffusive flow conductances has been experimentallydetermined for three species. Records of stomatal movementsin air of different compositions are presented. Key words: Stomata, porometry, diffusive and mass flow conductance     

Studies on air passage capacity of maize leaves at varying light intensities,temperatures and fertilization levels in field conditions

A new porometer operable in field conditions was used to study air passage capacity of maize(Zea mays) leaves in relation to light intensity, temperature and ferilization. In addition to light intensity, temperature was found to affect stomatal movement in a significant manner.     

A condensation type porometer for field use

A double cup transpiration porometer is described which simultaneously measures the resistance to water vapor diffusion from the upper and lower epidermises of a leaf. In use the cups are dried, the porometer is clamped on the leaf, and the transit time required for water vapor to condense on a cold (0 C) reflective surface in each cup is recorded. Since the sensing element remains at constant temperature, only transit time and leaf temperature are required to calculate leaf resistance.     

A simple porometer for precise recording of leaf resistance

A porometer, which can be easily constructed with a common photometricunit and yet records the air flow through a leaf blade accuratelyand sensitively, was developed and used to record the flow changesthrough Brassica chinensis leaves under several light, air andwater conditions. (Received May 17, 1973; )     

Das Seifenblasenporometer (Zur Messung der Stomaweite an Amphistomatischen Blättern)

Zusammenfassung Luft wird aus einer Porometerkammer durch ein amphistomatisches Blatt hindurchgedrückt, auf der anderen Seite des Blattes von einer zweiten Porometerkammer aufgefangen und einem Seifenblasenströmungsmesser zugeleitet. Es wird die Zeit gestoppt, die eine vom Gasstrom vorangetriebene Flüssigkeitslamelle braucht, um ein bestimmtes Rohrvolumen zu durchlaufen. Es handelt sich somit um eine absolute Meßmethode. Neue Untersuchungen Levys bestätigen die hohe Genauigkeit dieses Verfahrens zur Messung des Volumflusses von Gasen.Die Messung kann innerhalb einiger Sekunden erfolgen; sie erfordert keinen hohen applizierten Druck. So werden Fehler durch CO₂-Verarmung im Porometer, Stomareaktionen und elastische Dehnung des Blattes so klein wie möglich gehalten. Falschluft ist ausgeschlossen.Die Methode eignet sich auch fürs Freiland, mit Luft aus einer beschwerten Luftmatratze und einer rasch anzusetzenden Porometerklammer. Als Beispiel wird eine Durchflußtopographie eines Blattes gegeben

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The soap-bubble porometer (measuring stomatal width in amphistomatic leaves)

Summary Two identical porometer cups are attached in opposition to both sides of an amphistomatic leaf. Air pressure is supplied to one of them. The resulting flow of air through the leaf is fed into a soap-bubble flowmeter. The time needed by a lamella of soap solution to move through a known volume of the meter is taken. Recent investigations made by Levy confirm the high accuracy obtainable by this absolute method of measurement of volume flow.Measurements are possible within some seconds, no high pressure need be applied. Thus, errors are minimized, caused by CO₂ depletion within the porometer cups, by reactions of the stomata, and by elastic stretch of the leaf. Interference of false air is excluded.The method can be used in the field with air supplied by a weighted air-bed, and using a quick-fastening clip-type porometer. The topography of stomatal conductance of a leaf, obtained with the method described, is presented as an example.

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Mit 5 Textabbildungen     

Studies in Stomatal Behaviour: V. THE ROLE OF CARBON DIOXIDE IN THE LIGHT RESPONSE OF STOMATA

It was found that stomata on illuminated leaves, both of Pelargoniumand wheat, opened much wider where the leaf surface was enclosedin a small volume of air, as in a normal porometer cup, thanelsewhere. This was shown for both species by the infiltrationmethod, and for Pelargonium by Lloyd's method and direct microscopicalobservation also. The effect was shown not to be due to pressure of the porometercup or glass plate on the leaf, or to temperature differences,nor directly to the lack of movement or high humidity of theenclosed air. A considerable body of data was collected which appeared tosupport the hypothesis that the wide opening was due to accumulationof some volatile substance produced by the leaf, but all theresults were also consistent with the view that it was causedby reduction in the carbon dioxide content of the enclosed airbelow the normal 0·03 per cent. owing to photosynthesis.Further crucial experiments with both the porometer and infiltrationmethods left virtually no doubt that the latter hypothesis wascorrect. This extreme sensitivity of stomata to carbon dioxide concentrationwithin the range 0·03 per cent. to zero is discussedin relation to their operation in nature, and a possible biologicaladvantage is suggested. The bearing of the effect upon porometer investigations is alsodiscussed and it is concluded that for all quantitative or semi-quantitativeexperimentation it is essential to use a cup detached betweenreadings, or at least swept with air such as surrounds the restof the leaf, and to have the upper leaf surface above the cuparea freely exposed or similarly swept. For qualitative investigationof the light response of stomata the traditional form of cupmay be used. The importance is stressed of allowing porometer readings toreach equilibrium under one set of conditions before changingto another, when investigating the ‘closing’ or‘opening’ effects of external factors. Several subsidiary effects, observed in the course of the investigation,are discussed; in particular an effect of humidity upon therate of response to other factors.     

Studies in Stomatal Behaviour: The Effects of Moving, Normal and Carbon Dioxide-Free Air on the Stomata of Some Plants

A series of experiments were conducted to investigate the effects of moving, normal and carbon dioxide-free air on the stomata within porometer cups attached to the illuminated leaves of Datura stramonium, Pelargonium zonale, Duranta plumieri and Clerodendron inerme. A marked opening stomatal response was obtained in Datura and Pelargonium on changing to carbon dioxide-free air. In general no such response was established in Duranta and Clerodendron. Indications of even an opposite closing effect were shown in the case of Duranta. The present results seem to disprove the reduction of carbon dioxide by photosynthesis as the major factor controlling the wide stomatal opening within a porometer cup. The possibility of a humidity effect is also suggested.     

Changes in the Resistance of the Mesophyll Tissue 1

Porometer measurements of the resistance offered to viscousflow of air by mesophyll tissue rings cut from leaves were carriedout simultaneously with determinations of changes in tissuewater content, Decreases in water content were accompanied byincreases in mesophyll resistance and these changes are discussedin relation to porometer measurements of total resistance offeredby leaves to viscous flow of air.     

A Handpiece for the Simultaneous Measurement of Photosynthetic Rate and Leaf Diffusive Conductance: I. DESIGN

The design and construction of a handpiece for the simultaneousmeasurement of photosynthetic rate and diffusive conductanceof cereal leaves in almost natural conditions in the field isdescribed. Photosynthetic rate is found from the assimilationof ¹⁴CO₂ by part of the leaf which is temporarily enclosed ina small hand-held chamber. This chamber also acts as a stirred,steady-state water vapour diffusion porometer, allowing thesimultaneous measurement of relative humidity from which theleaf diffusive conductance is estimated. The instrument alsomeasures the leaf and air temperatures and incident photon fluxdensity. The important criteria of the performance of such ahandpiece are discussed, and the sensors which measure the physicalvariables of humidity, temperature, and photon flux densityare described. An automatic sequencing system built from logiccircuits which displays the measured values of these variablesand times the operations is also described.     

The Differential Transpiration Porometer

The construction and testing of a new differential transpirationporometer for stomatal measurements are described. The principleinvolved is explained, and the mathematical theory is dealtwith in an appendix. As a result of experiments comparing the new instrument's readingswith those obtained with a Wheatstone bridge porometer, a relationbetween diffusive conductance and viscous flow conductance isfound; in the case of wheat stomata this approaches a cubicrelation and in the case of Talinum triangulare a quadraticone.     

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     

Responses of apple leaf stomata to environmental factors

Abstract. Stomatal conductances ( g _s) were measured on the leaves of 3–4 year old Golden Delicious trees and of seedlings of two other cultivars. Measurements were made on container grown trees in the field with a diffusion porometer in 1975 and 1976, and in controlled conditions in a leaf chamber in the laboratory in 1976. Stomatal densities in the Golden Delicious leaves were assessed from scanning electron micrographs. Stomatal density on extension shoot leaves was higher than on other leaf types after June.
The response to irradiance shown by both the porometer and the leaf chamber results could be described by a rectangular hyperbola: where g _max is maximum conductance and β indicates the sensitivity of g_s to photon influx density ( Q _p). The values of β were in the range 60–90 μmol m⁻² s⁻¹.
There was no evidence that apple stomata are sensitive to temperature per se, but g _s was reduced by increasing leaf to air vapour pressure deficits ( D ). There was a linear relationship between g _s and D which was not attributable to feed-back to leaf water potential (ψ_L) as the latter did not affect g _s until a threshold of about −2.0 to −2.5 MPa was reached. Conductance generally declined with increasing ambient CO₂ concentration.     

Two types of ventilated porometers compared on broadleaf and coniferous species

Two ventilated porometers (diffusion and steady-state) were compared on four broadleaf and five coniferous species. The diffusion porometer gave consistently lower conductance values for both types of species, reflecting a direct stomatal response to low chamber humidity. At high conductance values, the porometers produced a linear and nearly equal response, but the diffusion porometer was less sensitive at low conductance values. This was due to lower air flow (20% of the velocity in the steady-state porometer) and water vapor sorption (by its acrylic plastic chamber). The broadleaf species had less variation (R² = 0.81) than did the coniferous species (R² = 0.61), but, with the latter, there was better correspondence between the two porometers, possibly due to sampling technique. Conductance values were clustered by species.     

Stomatal Opening as a Practical Indicator of Moisture Stress in Cotton

The response of stomata to varying soil moisture content was studied in cotton by means of a new type of porometer suitable for field work. The results showed that maximum stomatal aperture was only attained when soil moisture was near the upper limit of the so called “available range”. These results indicate the possibility of making practical use of the new type of porometer for the purpose of determining soil moisture deficiency under field conditions, thus aiding in irrigation practices.     

The Measurement of Stomatal Responses to Stimuli in Leaves and Leaf Discs

A comparison has been made of stomatal responses in intact leaves,leaf discs supplied with water via their cut edges and leafdiscs floating on water. Xanthium pennsylvanicum leaf discswatered via their cut edges appeared to be more turgid thanintact leaves; this considerably slowed down the rate of stomatalopening but it slightly increased the final steady-state stomatalopening. When the water potential of such leaf discs was loweredby pre-treatment with mannitol solutions rates of stomatal openingincreased whereas maximum steady-state openings decreased. In tobacco leaf discs floating on water the stomata in contactwith water were wider open than those in contact with normalair and they did not respond to treatment with carbon dioxide-freeair. The rate of photosynthesis was severely reduced in tobaccoleaf discs floating with the lower epidermis on water, mostprobably owing to the slow rate of diffusion of carbon dioxidein water. By floating such discs on osmotica the degree of stomatalopening was increased, however, a response to treatment withcarbon dioxide-free air was still not measurable. It is postulatedthat, on account of the relative unavailability of carbon dioxidefrom the water, the carbon dioxide concentration in the substomatalcavities of the lower surface is abnormally low, irrespectiveof whether ordinary air or carbon dioxide-free air is availableto the upper surface. A comparison between porometer readings and measurements ofsiliconerubber impressions of stomatal pores taken from insidethe porometer cup confirmed that the silicone-rubber impressionmethod of assessing stomatal responses to stimuli has severelimitations, especially at small stomatal apertures.     

Design calibration and field use of a stomatal diffusion porometer

Modifications of the design and calibration procedure of a diffusion porometer permit determinations of stomatal resistance which agree well with results obtained by leaf energy balance. The energy balance and the diffusion porometer measurements indicate that the boundary layer resistances of leaves in the field are substantially less than those predicted from heat transport formulas based on wind flow and leaf size.     

Stomatal Responses of Bean (Phaseolus Vulgaris L.) Leaves to Changing Irradiance,Air Humidity,and Water Potential of Root Medium

Stomatal responses of attached bean (Phaseolus vulgaris L.) leaves to changing spectral composition ("white" - WL., blue - BL, or red - RL radiation), air humidity (100 % or about 4 % RH), and water potential of the root medium (close to 0 or −1.2 MPa) were determined by air flow porometer. Opening of stomata always increased under BL and decreased under RL. In response to decline in air humidity, leaf conductance showed transient increase before it reached lowered steady state. BL enhanced and RL diminished this response. This revised version was published online in June 2006 with corrections to the Cover Date.