Showing papers on "Transpiration published in 1972"
TL;DR: For field conditions and for morphologically different types of photosynthesizing organs the results confirm former experiments carried out with isolated epidermal strips and proves that the stomatal aperture has a direct response to the evaporative conditions in the atmosphere.
Abstract: The stomata of plants growing in the Negev Desert, namely the stomata of the mesomorphic leaves of Prunus armeniaca, the xeromorphic stems of Hammada scoparia, and the succulent leaves of Zygophyllum dumosum, respond to changes in air humidity. Under dry air conditions diffusion resistance increases. Under moist air conditions diffusion resistance decreases. When the stomata close at low air humidity the water content of the apricot leaves increases. The stomata open at high air humidity in spite of a decrease in leaf water content. This excludes a reaction via the water potential in the leaf tissue and proves that the stomatal aperture has a direct response to the evaporative conditions in the atmosphere. In all species the response to air humidity is maintained over a period of many hours also when the soil is considerably dry. The response is higher in plants with poor water supply then in well watered plants. Thus for field conditions and for morphologically different types of photosynthesizing organs the results confirm former experiments carried out with isolated epidermal strips.
278 citations
TL;DR: A model of the mechanism causing sustained oscillations, in stomatal conductance, in a cotton plant exhibiting sustained oscillatory behaviour is developed and is shown to have many of the characteristics of free-running oscillations in real plants.
Abstract: Measurements of transpiration, leaf water content, and flux of water in a cotton plant exhibiting sustained oscillations, in stomatal conductance are presented, and a model of the mechanism causing this behaviour is developed. The dynamic elements, of the model are capacitors—representing the change of water content with water potential in mesophyll, subsidiary and guard cells—interconnected by resistances representing flow paths in the plant. Increase of water potential in guard cells causes an increase in stomatal conductance. Increase of water potential in the subsidiary cells has the opposite effect and provides the positive feed-back which can cause stomatal conductance to oscillate. The oscillations are shown to have many of the characteristics of free-running oscillations in real plants. The behaviour of the model has been examined, using an analogue computer, with constraints and perturbations representing some of those which could be applied to real plants in physiological experiments. Aspects of behaviour which have been simulated are (a) opening and closing of stomata under the influence of changes in illumination, (b) transient responses due to step changes in potential transpiration, root permeability and potential of water surrounding the roots, (c) the influence of these factors on the occurrence and shape of spontaneous oscillations, and (d) modulation of sustained oscillations due to a circadian rhythm in the permeability of roots.
162 citations
TL;DR: In this paper, a model was used to evaluate the relative importance of environmental variables in influencing leaf temperature, transpiration, and primary production of mangrove stands, and showed that the environmental variables with the greatest influence on primary production were air temperature and humidity, and leaf water deficits did not develop within the canopy in either June or January.
Abstract: used as input data for the model. The model produced realistic leaf temperatures, leaf resistances, transpiration rates, and primary production rates and was used to indicate the relative importance of environmental variables in influencing leaf temperature, transpiration, and primary production. Maximum leaf temperatures occurred at the top of the canopy in June and the overcast day in January, but at the bottom of the canopy on the clear day in January. The model presently calculates water uptake as a constant rate to leaves and does not include a redistribution of water within the plant. The calculated transpiration was about 20% of the total water loss of the stand, the remaining loss coming directly from the moist substrate under the canopy. The inclusion in the model of stomatal movements reduced daily transpiration under conditions of mild water stress by 0.04 cm day-1. Total evapotranspiration was 0.67 cm day-', and transpirational water loss was 0.12 cm day-'. Levels in the middle of the canopy had the highest transpiration rate because of their high leaf area, but leaves at the top had the highest transpiration rate per unit leaf area. Leaf water deficits great enough to initiate stomatal closure occurred early in the morning at the top of the canopy in June on clear days, later in the morning at the top of the canopy in June on cloudy days, early in the afternoon at the top of the canopy in January on clear days, and not at all at the top of the canopy in January on cloudy days. Leaf water deficits did not develop within the canopy in either June or January. Net photosynthesis calculated with the model was 5.6 g organic matter m-2 day-' for sunny days and 3.5 for cloudy days in June. Gross photosynthesis per unit leaf area was greater at the top of the canopy than at the bottom, but the middle levels of the canopy had the greatest production. The efficiency of water utilization increased from top to bottom of the canopy. A weighted monthly estimate for production was 3.4 for June and 2.2 for January, giving an average annual net production rate of 2.8 g organic matter m-2 day-'. The model predicts that the maximum photosynthesis for mangrove stands will occur with a leaf-area index of about 2.5 if no acclimation to shade within the canopy occurs. A leaf area greater than about 2.5 may decrease production. The environmental variables with the greatest influence on primary production were air temperature and humidity. Production was decreased by increasing air temperature and increasing humidity. Increasing total solar radiation increased production up to a point, then decreased it. Increasing the diffuse fraction of the total solar radiation increased production. Increasing infrared radiation decreased production. Production and transpiration increased with increasing leaf-area index
81 citations
TL;DR: Leaf temperatures associated with torn and untorn leaves of Musaceae were taken in both dry and wet seasons at Barro Colorado Island, Canal Zone and analyses showed that leaves less than 10 cm wide are not subject to critical heat stress, have lower water loss, and higher ratios of photosynthesis to water expended than do leaves of widths greater than 10cm.
Abstract: Leaf temperatures associated with torn and untorn leaves of Musaceae were taken in both dry and wet seasons at Barro Colorado Island, Canal Zone. Transpiration rates and leaf resistance to water—vapor diffusion were determined. Energy—budget analysis is used to describe the relationship of leaf dimension and leaf resistance to thermal survival and water usage. Gas—exchange theory is applied to predict the photosynthetic implications of leaf tearing. The analyses showed that leaves less than 10 cm wide are not subject to critical heat stress, have lower water loss, and higher ratios of photosynthesis to water expended than do leaves of widths greater than 10 cm. In wet season, leaves have lower resistance to the diffusion of water vapor and accordingly are less subject to excessive heating.
72 citations
TL;DR: In this paper, a single surface application of abscisic acid or its methyl and phenyl esters suppressed stomatal opening on leaves of Xanthium strumarium.
Abstract: A single surface application of abscisic acid or its methyl and phenyl esters suppressed stomatal opening on leaves of Xanthium strumarium. The effect was restricted to the treated parts of the leaf blades, there being no detectable translocation to untreated parts. There were no increases in CO2 compensation to which stomatal closure could be attributed.
Abscisic acid and its esters acted successfully as antitranspirants when applied once to leaf surfaces of young barley plants. Over a 9-day period there was a reduction of about 50% in the amount of water transpired without any detectable reduction in the rate of dry weight increase. The treatments reduced transpiration relatively more than dry matter accumulation, and hence there was an increase in the water use efficiency. The effect of the treatments became progressively less over 9 days, but even at the end of the experiment (day 9) both the esters reduced transpiration by 20–25%. The esters were slightly more effective than abscisic acid itself.
On the basis of the data presented here, field trials of the antitranspirant properties of these compounds are recommended.
70 citations
TL;DR: Water in the transpiration stream is distributed throughout the leaves in the vascular bundles in broad bean, laurel, and plantain, indicating that the cuticle of the epidermis is the main evaporating surface of the leaf.
Abstract: Water in the transpiration stream is distributed throughout the leaves in the vascular bundles. In wheat, water appears to be confined to the main veins by the mestome sheath and to enter the mesophyll through the walls of the smaller veins. Within the mesophyll the water in the transpiration stream moves in the free space of the cell walls to the evaporating surfaces of the leaf. The lead chelate, which is used to trace the transpiration stream, accumulates at the final points of evaporation at the margin of the leaf. Lead chelate accumulates beneath and on the surface of the cuticle, being partly associated with the anticlinal walls of the epidermal cells, the walls of the stomatal guard cells and specialized epidermal cells. Chelate does not accumulate at the base of substomatal cavities, indicating that the cuticle of the epidermis is the main evaporating surface of the leaf. The behaviour in broad bean, laurel, and plantain is essentially the same. The rate of peristomatal and cuticular transpiration is closely related to the size of the stomatal aperture. Conditions which control stomatal aperture also cause changes in the dimensions of the epidermal cells.
69 citations
TL;DR: In this paper, the influence of potassium on the transpiration rate of Triticum aestivum and Pisum sativum grown in nutrient solutions was investigated, and it was found that plants with high amounts of potassium were found to have the lowest transpiration rates.
Abstract: The investigation concerns the influence of potassium on the transpiration rate of Triticum aestivum and Pisum sativum grown in nutrient solutions. Plants with high amounts of potassium were found to have the lowest transpiration rates. Shoot/root ratio, stomatal frequency, and stomatal aperture were correlated with the potassium concentration in the leaves. In Triticum no correlations with leaf concentration of Na were evident.
Short term experiments were carried out in order to investigate the effects on the transpiration rate of a sudden increase in potassium concentration in the nutrient solution. An addition of potassium chloride to potassium deficient wheat plants resulted in a decrease in the transpiration rate of up to 50% within two hours. Comparative tests with sodium chloride resulted in a decrease in transpiration rate of the same magnitude, indicating that the short-time reaction is not specific to potassium.
The experiments show that the transpiration rate can be regulated by varied potassium and sodium concentrations. The observed effect is supposed to be due to changes in the stomatal aperture.
65 citations
TL;DR: In a short experiment a rise in root temperature up to 40°C caused an increase in transpiration and a decrease in the resistance of the leaves to the passage of water vapor, whereas in prolonged experiments transpiration reached a maximum and leaf resistance a minimum at 30°C and the leaf water potential increased also with increasing root temperature.
Abstract: Ungrafted apple rootstocks were grown in sand cultures at constant root temperatures between 20°C to 40°C. Temperatures of 30°C and above reduced root and shoot growth. Serious damage to the leaves occurred at 35°C and above.
The O2 consumption, CO2 evolution and respiratory quotient (RQ) of the roots showed maximum values at 35°C.
Different rootstock cultivars varied greatly in their susceptibility to damage by supraoptimal root temperatures apparently due to anaerobic respiration. The more susceptible ones differed from resistant types in the larger amount of ethanol they accumulated in their roots at supraoptimal root temperature, and the more severe reduction in the malic acid content of the roots at such temperature. Acetaldehyde was also found in roots and leaves at supraoptimal root temperatures, whereas the organic acid content of the leaves tended to decrease.
Supraoptimal root temperature also caused a reduction of cytokinins in both roots and leaves accompanied by a reduction in the leaf chlorophyll content. This could be prevented by the application of kinetin or benzyladenine to the leaves.
In a short experiment a rise in root temperature up to 40°C caused an increase in transpiration and a decrease in the resistance of the leaves to the passage of water vapor, whereas in prolonged experiments transpiration reached a maximum and leaf resistance a minimum at 30°C. The leaf water potential increased also with increasing root temperature. Leaf temperature increased with increasing root temperature, irrespective of increasing or decreasing transpiration rates.
61 citations
TL;DR: In this paper, the relative importance of the stomata in restricting C02 uptake under conditions of water stress was determined from measurements of the rates of assimilation and transpiration and the corresponding concentration gradients of C02 and HaO vapour.
Abstract: An attempt was made to determine the relative importance of the stomata in restricting C02 uptake under conditions of water stress. The air-phase and liquid-phase resistances to uptake of C02 were determined from measurements of the rates of assimilation and transpiration and the corresponding concentration gradients of C02 and HaO vapour. The results showed that the air-phase resistances (stomata) could account for only half the reduction in the rate of photosynthesis accompanying water stress. Experiments in which air was passed through the leaf confirmed that water stress restricted C02 fixation within the leaf itself. The results and their possible explanation are discussed in relation to other work.
59 citations
TL;DR: In this article, the response of southern peas (Vigna sinensis L. Endl. var. Burgundy) to different levels of water deficit at three different stages of growth was measured in a greenhouse.
Abstract: Response of southern peas (Vigna sinensis L. Endl. var. Burgundy) to different levels of water deficit at three different stages of growthw as measured in a greenhouse. In each stage, plants were stressed to three levels of leafwater potential: — 14 bars, — 21 bars, and — 28 bars. Crop susceptibility factors (fractional reductions in yield compared to a nonstressed treatment) were determined for each stage of growth and level of plant water deficit. The flowering period was found to be the most sensitive stage, regardless of deficit level. The pod development stage was found to be least sensitive to level of deficit. A water deficit of — 28 bars, however, caused a yield reduction of greater than 50% for all growth stages. Stress-day index values were calculated and related to crop yield. The use of the stress-day index concept in irrigation scheduling is discussed. Leaf water potential varied linearly with soil water potential between 0 and — 15 bars. Leaf diffusion resistance became high and transpiration was negligible after the leaf water potential reached — 10 to — 12 bars; the corresponding soil water potential was — 5 bars. Water-use efficiencies were highest for the nonstressed treatment and the treatment with the low deficit level during the first stage.
56 citations
TL;DR: Under field and laboratory conditions, vapor pressure deficit and water stress were significant factors influencing transpiration and Phenological stage was a major factor in the transpirational relationships of both species in the field.
Abstract: Atriplex confertifolia and Eurotia lanata plants were studied in the field and laboratory under controlled conditions of temperature and vapor pressure deficit with uniform wind speed and light intensity and various levels of water stress. Multiple regression analysis indicated that under both field and laboratory conditions, vapor pressure deficit and water stress were significant factors influencing transpiration. Phenological stage was also a major factor in the transpirational relationships of both species in the field. Transpiration rates under comparable conditions tended to be higher for Eurotia than for Atriplex on a leaf dry weight basis with less pronounced differences on a leaf area basis. However, in the latter part of the summer, transpiration rates of Eurotia decreased markedly while Atriplex tended to maintain active transpiration. Under laboratory conditions both species exhibited transpiration at plant moisture stress values as great as 115 bars.
TL;DR: Leaf resistances in low temperature pretreated plants were higher than in controls or high temperature Pretreated plants at leaf temperatures between 5 and 25 C, Thus, the pretreatment influenced stomatal aperture.
Abstract: Leaf resistance for water vapor (total diffusion resistance minus boundary layer resistance), transpiration, and leaf temperature were measured in attached leaves of greenhouse-grown Xanthium strumarium L. plants that had been pretreated for 72 hours with high (40 C day, 35 C night), or low (10 C day, 5 C night) air temperatures. Measurements were made in a wind tunnel at light intensity of 1.15 cal cm−2 min−1, air temperatures between 5 and 45 C, and wind speed of 65 cm sec−1. Leaf resistances in low temperature pretreated plants were higher (8 to 27 sec cm−1) than in controls or high temperature pretreated plants (0.5 to 3 sec cm−1) at leaf temperatures between 5 and 25 C. Thus, the pretreatment influenced stomatal aperture.
TL;DR: No evidence that in short-term experiments simazine has an effect on active transport processes is found, except in so far as this affected movement of water, and micro-organisms present on the plant roots at ambient laboratory levels had no effect on the uptake and transport of the herbicide.
Abstract: The factors affecting the absorption and translocation of simazine by young barley plants in short-term experiments in water culture have been investigated. Chromatographic examination of the xylem sap indicated no extensive breakdown of the herbicide in the transpiration stream. Under varying conditions of humidity, light intensity, temperature, and in the presence of metabolic inhibitors, the concentration of simazine in the trans piration stream relative to that in the uptake medium was always less than unity. This could, in part, be attributed to retention of simazine at a higher concentration on a fresh weight basis in the root tissues than in the ambient medium. There was little evidence that the absorption and translocation of simazine was influenced by metabolism except in so far as this affected movement of water, and micro-organisms present on the plant roots at ambient laboratory levels had no effect on the uptake and transport of the herbicide. Simazine brings about a decrease in the rate of transpiration and a reduction in the total uptake of rubidium and phosphate at relatively high concentrations. However, when the phosphate concentration in the ambient medium was below the level at which translocation of this ion is affected by the rate of transpiration, the herbicide did not reduce uptake of phosphate. There is therefore no evidence that in short-term experiments simazine has an effect on active transport processes.
TL;DR: The photosynthetic advantage of individual grass leaves compared with legumes was reflected in higher productivity of whole plants and, to a lesser extent, of grass swards, and it is an important determinant of the lower transpiration ratios of grasses at leaf, plant, and sward levels.
Abstract: Differences in leaf net photosynthetic rate were associated with differences in intracellular resistance. The larger intracellular resistance of legume leaves appeared to result from larger resistances to the movement of CO from the mesophyll cell wall to the photosynthetic sites rather than from high resistances associated with its fixation at the sites. Photorespiration could not be detected in grasses but their dark respiration rates at normal ambient CO concentrations were higher than the values for legumes. Although legumes had an appreciable photo respiration rate, this alone could not account for their lower photosynthetic rates. The higher intracellular resistance appeared to be an equally important factor. The photosynthetic advantage of individual grass leaves compared with legumes was reflected in higher productivity of whole plants and, to a lesser extent, of grass swards. Furthermore, it is an important determinant of the lower transpiration ratios of grasses at leaf, plant, and sward levels.
TL;DR: In this paper, the authors found that the daily total transpiration was linearly related to heat pulse velocities measured once each day at mid-day or averaged for 4- to 14-hour periods centred on midday.
TL;DR: A digital registration system used with temperature- and humidity-controlled cuvettes for net photosynthesis and transpiration measurements in the field is described and the sizeable influence of errors in humidity and temperature measurements on the calculated diffusion resistance is demonstrated.
Abstract: A digital registration system used with temperature- and humidity-controlled cuvettes for net photosynthesis and transpiration measurements in the field is described. The associated errors of the measured parameters and calculated data are estimated. The digitalization is based on an analogue registration which is of primary importance in the control of experimental conditions in the cuvettes. The digital system is connected to the analogue registration in series. The error associated with digitalization is 0.1% across 70% of the scale. This error increases to 0.2% between 3 and 30% on the scale due to a minor lack of linearity. The reproducibility of the digitalization is ±0.024%.The error associated with data transfer in the digitalization and the errors of the analogue registration are estimated for temperature and humidity measurements (error of air and leaf temperature is ±0.1° C; error of the dew point temperature is ±1.1° C dew point). The effect of these errors on the calculation of relative humidity and the water vapour difference between the leaf and the air is determined using the progressive error law. At 30° C and 50% relative humidity, the error in relative humidity is ±7.4%, the error for the water vapour difference is ±6.6%. The dependence of these errors on temperature and humidity is shown.The instrument error of the net photosynthesis measurement is calculated to be ±4.2%. Transpiration measurements have an average inaccuracy of ±8.3%. The total diffusion resistance which is calculated from values of transpiration and the water vapour difference has an average error of ±10.9%. The sizeable influence of errors in humidity and temperature measurements on the calculated diffusion resistance is demonstrated. The additional influence of biological errors associated with field measurements is discussed.
TL;DR: In this paper, a semi-closed compensating system is described for measuring CO2 exchange and transpiration simultaneously under controlled environmental conditions, which permits conditions in the assimilation chamber to be kept uniform and within narrow limits.
Abstract: A semi—closed compensating system is described for measuring CO2 exchange and transpiration simultaneously under controlled environmental conditions. The compensating feature permits conditions in the assimilation chamber to be kept uniform and within narrow limits. Temperature, relative humidity, carbon dioxide concentration, wind speed, and light intensity may be varied within the system. Since transpiration and photosynthesis can be measured simultaneously, diffusive resistances to carbon dioxide and water transport may also be calculated from the data. The performance of the apparatus was checked with Ambrosia trifida L. Net photosynthesis occurred at a rate of 32 mg hr—1 dm—2 of leaf area and 30°C under saturating light intensities, and transpiration took place at 5.3 gm hr—1 dm—2 under the same conditions. Both processes were sensitive to CO2 concentrations from 100 to 400 ppm and the temperatures between 15° and 30°C. Respiration was relatively insensitive to temperature below 20°C. Although the re...
TL;DR: Hourly trends in stomatal resistance and water potential of the upper leaves of sorghum and of soybean canopies tended to parallel each other and the profiles of temperature and water-vapour pressure were consistent with the profile of canopy transpiration resistance.
Abstract: Summary
Hourly trends in stomatal resistance and water potential of the upper leaves of sorghum and of soybean canopies (measured with diffusion porometer and thermocouple psychrometer) tended to parallel each other. Vertical profiles (both canopies) indicated that the stomatal resistance of the lower leaves usually was greater than that of the upper leaves. The position of minimum resistance varied with time of day. The profiles of temperature and water-vapour pressure were consistent with the profile of canopy transpiration resistance. The upper sorghum leaves had a lower water potential than the lower leaves. In the morning a strong gradient of water potential existed from lower to upper leaves in plants in both canopies; in the afternoon the gradients continued in sorghum but disappeared in soybean plants.
TL;DR: Autumn transpiration evidently continues unabated in green leaves but declines to small values when leaves turn color, and the value of leaf resistance to vapor flow remains at the low values found in summer.
Abstract: Leaf resistance to vapor flow was measured with a diffusion porometer on hardwood trees in central New Hampshire during autumn senescence and was compared with leaf color and chlorophyll content. Daytime diffusion resistance remained at the low values found in summer (1–10 sec/cm) as long as the leaves remained green. Resistances ranged from 5 to > 35 sec/cm when chlorophyll content was below 0.4 mg/g of fresh weight and leaf color was yellow green or yellow. Autumn transpiration evidently continues unabated in green leaves but declines to small values when leaves turn color.
TL;DR: Leptadenia pyrotechnica (Forsk) grows in valleys of the Eastern Desert in Egypt where the climatic and edaphic drought is very severe as discussed by the authors.
Abstract: 1.
Leptadenia pyrotechnica (Forsk.) Decne. grows in valleys of the Eastern Desert in Egypt where the climatic and edaphic drought is very severe.
2.
The transpiration rate is low in winter months and rises by the onset of summer. The rise in transpiration rate is not comparable with that of the evaporation.
3.
The maximum transpiration rate is generally attained earlier than the maximum of the evaporating factors, specially in summer. The transpiration curves show a rapid decrease after this maximum despite the continuous rise of the evaporating power of the atmosphere. This points to an effective stomatal regulation.
4.
The osmotic pressure ofLeptadenia is relatively low. The osmotic pressure values show narrow daily and seasonal fluctuations.
5.
Leptadenia pyrotechnica is one of the most drought resistant plants. Its xeromorphic leafless habit implies reduction in the transpiring surface, while its deep extensive roots and low transpiration rate ensure a favourable water balance. The mechanisms of drought resistance in this plant were discussed.
TL;DR: In this paper, the concentrations of atrazine in the shoots of wheat plants growing in 12 different soils were directly proportional to the soil solution concentrations of herbicide estimated from slurry adsorption measurements.
Abstract: The concentrations of atrazine in the shoots of wheat plants growing in 12 different soils were directly proportional to the soil solution concentrations of herbicide estimated from slurry adsorption measurements. There was a marked discrepancy between the total uptake of herbicide and the amount theoretically supplied by mass-flow in response to transpiration. This discrepancy was less when plants were grown in nutrient solutions. In an experiment with one soil only, the half-life of atrazine was 22 days and when the solution concentration in this soil was corrected for this change, a much closer prediction of atrazine uptake could be obtained. The ways in which interactions between adsorption, breakdown and transpiration rates may affect herbicide toxicity under field conditions are discussed.
Journal Article•
TL;DR: The controlling factor in water use is basically the moisture status of the soil surface, and how frequently the surface receives water from rain or irrigation—along with the weather conditions—largely determines evapotranspiration rates.
Abstract: Not Available – First paragraph follows:
The weather largely determines the use of water, or evapotranspiration (ET), by most crops during times when the plants are healthy and fully shade the ground. Even under full-cover conditions, however, the evapotranspiration of various crops can vary significantly with differences in stomatal or surface resistance, reflectance, and aerodynamic roughness. However, during early stages of crop growth, transpiration is very limited, and the controlling factor in water use is basically the moisture status of the soil surface. How frequently the surface receives water from rain or irrigation—along with the weather conditions—largely determines evapotranspiration rates.
TL;DR: Transpiration rates were inversely related to body weight, directly related to surface area between 35 and 40° in large specimens and increased with death in Orthoporus ornatus, and desiccation resistance in O. ornatus is considerably greater than in millipedes previously studied.
TL;DR: In this article, the effects of either coating the leaf to make its surface impermeable to water vapour, or wetting the leaf surface, or shading it were considered, and the results obtained by the various methods are roughly similar, but anomalies need further investigation.
TL;DR: The model presented, which the authors refer to as TRALF, is an attempt to simulate the transpiration rate of a non-growing leaf throughout a day under varying environmental conditions using time intervals in the order of 10 sec.
Abstract: The model presented, which we refer to as TRALF, is an attempt to simulate the transpiration rate of a non-growing leaf throughout a day under varying environmental conditions using time intervals in the order of 10 sec. Stomata play a key role in the control of the transpiration process. Therefore special attention is paid to stomatal properties and factors governing stomatal aperture namely, plant water status, C02 concentration and light intensity. Endogenous rhythms of stomata and long term trends of stomatal osmotic potential are not considered. The equations by which the energy and gaseous exchange from irradiated and evaporating wet surfaces may be calculated, are well known (Slatyer 1967). Using such equations and some widely accepted assumptions concerning cuticular and stomatal diffusive resistances, a static model of leaf transpiration may be built, from which the constant equilibrium leaf temperature and transpiration rate can be derived. In a dynamic model the continuously changing leaf water status and the time-dependent behaviour of stomata should be considered. In order to achieve this a balance of water lost and gained by the leaf and the root must be kept. The stomatal aperture, which determines stomatal resistance, is the resultant of the relative water content of the guard cells and surrounding epidermal cells. Both follow the relative leaf water content with a time lag. Due to the special shape of guard cell walls an increase in volume of guard cells causes the stomata to open and vice versa. Subsidiary cells, neighbouring cells of stomata, are quantitatively less important and are supposed to work in the opposite way (Meidner & Mansfield 1968). As a rule stomata open in light and close in the dark. Careful experiments have shown that the low internal C02 level in light, due to photosynthesis, causes stomata to open (Heath & Milthorpe 1950). A slight opening may also be induced by a direct influence of light (Kuiper 1961). It is supposed that the C02 and light effects occur only in the guard cells as these are usually the only cells in the epidermis containing chloroplasts. The mechanism by which C02 concentration influences stomatal aperture is not known and statements about relative influences of water, C02 and light are essentially estimates. Most of the data in the literature about stomata have been obtained from many different species. Few theories have been formulated dealing with all aspects of stomatal functioning. Those that do exist contain a considerable degree of uncertainty about the relations between various processes and the magnitude the parameters involved (Woo, Stone & Boersma 1966; Raschke 1970). A more complete model, however, gives a better insight into the transpiration process and acts as a guide for further investigations into plant and crop transpiration. The model presented here is written in the simulation language Continuous System Modelling Program (IBM 1969), which has proved to be suitable for the programming of
TL;DR: Phenyl mercuric acetate, 8-hydroxyquinoline, N-dimethylamino succinamic acid, or 2-chloroethyl trimethyl ammonium chloride was sprayed on 37-day-old tomato plants seven times at weekly intervals to cause earlier flowering and plants of nearly normal appearance resulted with all treatments.
Abstract: Phenyl mercuric acetate, 8-hydroxyquinoline, N-dimethylamino succinamic acid, or 2-chloroethyl trimethyl ammonium chloride were sprayed on 37-day-old tomato (Lycopersicon esculentum Mill. cv. Sioux) plants seven times at weekly intervals. Plants of nearly normal appearance resulted with all treatments except 2-chloroethyl trimethyl ammonium chloride. There was no change in leaf number, but 2-chloroethyl trimethyl ammonium chloride increased the number of flowers. 2-Chloroethyl trimethyl ammonium chloride and phenyl mercuric acetate caused earlier flowering. Yield was not affected significantly. Stomatal opening was reduced 80% immediately after spraying with phenyl mercuric acetate or 2-chloroethyl trimethyl ammonium chloride, but 6 days after spraying, the reduction in stomatal opening was only 30 to 40%. Wilting was delayed 8 days by phenyl mercuric acetate and 4 days by 2-chloroethyl trimethyl ammonium chloride and N-dimethyl amino succinamic acid treatments, when water was withheld 59 days after the final spray application.