Stomatal Resistance Measurements Research Articles

Determining Regression Models for Photosynthesis and Stomatal Resistance as Affected by Temperature and Light Intensity in Tomato (Lycopersicon Esculentum Mill.) and Eggplant (Solanum Melongena L.) Grown in Glasshouses

This study was carried out to examine the relationships between net leaf photosynthesis and temperature and light intensity, between stomatal resistance and temperature and light intensity in tomato and aubergine grown with a range temperature from 10 to 30 °C and different light intensities from 3 to 7 MJm-2 d-1. The study was carried out in a six-compartment greenhouse (size 4 m * 8 m), the temperature of which can be controlled by air conditioning, on tomato and eggplant plants. Each of the six greenhouse compartments was set to have maximum temperatures of 10, 12, 16, 18, 20 and 24 °C. Commercial varieties named "Counter" for tomato and "Bonica" for eggplant were used. "Fisons M2" commercial compost was used in all growing media and nutrient was applied equally. In the study, different sowing and planting dates were applied to benefit from natural light conditions (between 3 and 7 MJm-2d-1). Average temperature in each compartment was recorded using a 'Combine' data logger at 15 minute intervals. A porometer (Delta-T device, MT -3) was used to measure the stomatal resistance of tomato and eggplant leaves. The stomatal resistance measurements of the plants were made at the same time of the day (between 11.00-13.00) at 15-day intervals at the top, middle and lower levels of the crown of four different plants in different environmental conditions. In tomato, leaf photosynthesis increased curvilinearly with temperatures up to about 20.5 °C at low light intensity and declined at higher temperatures. The highest photosynthesis was obtained from the plants grown at a temperature of 22.5 °C and 7 MJm-2d-1 light intensity. The lowest photosynthesis was at 10 °C and 3 MJm-2d-1. In aubergine, at low light intensities, net photosynthesis increased curvilinearly up to 23 °C while it increased up to 20 °C at high light intensities and declined at higher temperatures. Maximum net leaf photosynthesis was found to be greater in tomato than aubergine.

Effects of a set of water restrictions on potted ornamental crops grown in greenhouses – influence on New Guinea impatiens quality

Since agriculture is known as the main consumer of water in the world, reducing water inputs to crops appears a real challenge. This is true in particular in greenhouse ornamental systems, where a compromise must be found to reduce water inputs without impacting plant quality. Indeed, it is known that water restriction tends to limit plant height and leaf surface, and the resulting final architecture may not fulfil criteria for commercialization. Water savings must then be balanced with the quality loss. In order to understand the effect of limited irrigation on potted New Guinea impatiens, an experiment was conducted in a 100-m2 greenhouse compartment on plants distributed on four shelves irrigated with different water inputs, 8 weeks after repotting. Irrigation was maintained at 25, 50, 75 and 100% of the effective transpiration of the most-irrigated shelf. Plant growth parameters [leaf area index (LAI), height, fresh and dry weight] were monitored until the 16th week, and the final plant architectures of the shelves were compared. Measurements of stomatal resistance were performed and the water-use efficiency (WUE) was also calculated. Measurements showed that irrigation at a 25% level appeared to be inadequate and led to plant death. However, plants irrigated at 75% displayed similar growth to the 100% shelf, suggesting that a significant water saving could be obtained. Branching was the same for 50, 75 and 100% treatments. Although the plants of the 50% treatment did not die, they were less developed than those supplied with 75 and 100%, particularly concerning accumulated dry matter production and plant height. The WUE of plants in different treatments varied with time because of stomatal resistance regulation of the transpiration, whereas plants irrigated at 100 and 75% had similar WUE.

How sensitive is the CWSI to changes in solar radiation?

Cloud cover drastically and instantaneously reduces net radiation and available energy. Appearance of clouds will therefore alter the surface energy balance and elicit response of plant canopy temperature (T C). The attenuated shortwave radiation and altered T C during the presence of clouds may subsequently affect the crop water stress index (CWSI). Therefore, to correctly interpret T C measurements, the effect of clouds must be understood. The objective of this work was to study the effect of abrupt changes in solar radiation due to varying cloudy conditions on T C and CWSI for olive trees. Results from two separate experiments are presented, both comparing different levels of water status of Barnea olive trees. The first experiment was conducted in a commercial orchard where five irrigation levels were applied. Thermal images were acquired simultaneously with stomatal resistance measurements on a day with clear skies. The second experiment was conducted on single trees planted in lysimeters. Irrigation was withheld for five of 15 trees for 6 days until they were severely stressed. Thereafter, irrigation was resumed to levels higher than the transpiration rates. Throughout the stress and recovery periods, water status measurements were conducted daily between 12:00 and 14:00 on all trees. On the day of maximum stress, thermal images of well-watered and stressed trees were acquired every minute throughout a time sequence during which large fluctuations in radiation due to cloud cover were observed. The most pronounced result of this study was the greater response of stressed, compared to well-watered, trees to abrupt changes in radiation intensity. When solar radiation was high, the CWSI of stressed trees reached 0.8, while the CWSI of well-watered trees was near 0. When solar radiation dropped due to clouds, the CWSI of the stressed trees decreased to ∼0.3, while that of well-watered trees continued to fluctuate around 0. This finding implies that application of thermal imagery for water status detection would require very high radiometric resolution and constant reference measurements. For routine monitoring in commercial olive orchards, this could be facilitated by strategic maintenance of a few well-watered trees.

Potential evapotranspiration from forest and pasture in the tropics: A case study in Kona, Hawai‘i

► Potential evapotranspiration (PET) is low on leeward Hawai‘i Island. ► In this tropical region without water stress, PET is higher in pasture than in forest. ► Aerodynamic and stomatal control of PET differ for the two vegetation types. ► Land use changes such as increased cattle grazing may impact rates of PET. ► Forest conversion in tropical montane landscapes could affect downstream water users. Forest conversion in tropical montane landscapes is widespread and has potentially large implications for both biological and physical processes. Understanding the ecohydrologic processes that affect water can help efforts to predict the downstream effects of parcel-scale land use change. Differences in evapotranspiration between trees and grasses in humid, low wind environments are understudied, however. We analyze predictions of the Penman–Monteith model of potential evapotranspiration (PET) based on hourly meteorological inputs and direct measurements of stomatal resistance for leeward Hawai‘i Island. While evapotranspiration is very low in all of these forest and pasture ecosystems, modeled PET from pasture is higher than is PET from forest. The balance between aerodynamically and stomatally controlled evapotranspiration differs significantly between the two vegetation types in such a way that the weighted sum of the two components yields lower overall PET at the forest sites. The interaction of aerodynamic and stomatal control on PET, in conjunction with tropical meteorology characterized by low wind speeds and low vapor pressure deficit (VPD) causes this unexpected phenomenon. Vegetation structure plays an important role: evapotranspiration from forest is increased considerably by contributions from the understory, while the shorter the stature of pasture grass, the higher its rate of PET. In tropical regions that do not experience water stress, grassland has the potential to transport as much or more water vapor to the atmosphere than does forest.

Influence of ploidy level on morphology, growth and drought susceptibility in Spathiphyllum wallisii

In this study, we analysed morphological, anatomical and physiological effects of polyploidisation in Spathiphyllumwallisii in order to evaluate possible interesting advantages of polyploids for ornamental breeding. Stomatal density was negatively correlated with increased ploidy level. Stomatal size increased in polyploids. Tetraploid Spathiphyllum plants had more ovate and thicker leaves. The inflorescence of tetraploids had a more ovate and thicker spathum, a more cylindrical spadix and a thicker but shorter flower stalk. Biomass production of the tetraploids was reduced, as expressed by lower total dry weights, and tetraploids produced fewer shoots and leaves compared with their diploid progenitors. Furthermore, tetraploid Spathiphyllum plants were more resistant to drought stress compared with diploid plants. After 15 days of drought stress, diploids showed symptoms of wilting, while the tetraploids showed almost no symptoms. Further, measurements of stomatal resistance, leaf water potential, relative water content and proline content indicated that the tetraploid genotypes were more resistant to drought stress compared with the diploids.

SIMULTANEOUS RESPONSE OF STEM DIAMETER, SAP FLOW RATE AND LEAF TEMPERATURE OF TOMATO PLANTS TO DROUGHT STRESS

One of the many opportunities of direct crop monitoring is the ability to detect suboptimal growth conditions in a very early stage, so that both productivity and quality can still be guaranteed. In this study, eight tomato plants (Lycopersicon esculentum Mill. 'Clothilde') were hydroponically grown in order to modulate the root zone. Four of these plants were subjected to drought stress by adding 200 g/L poly-ethylene glycol 6000 to the nutrient solution. This treatment immediately resulted in a considerable reduction in sap flow rate, thereby forcing the plants to use their internal water storage to support transpiration. Consequently, a stem diameter shrinkage of 0.1 mm was measured before visual symptoms of turgidity loss were observed. At leaf level, the leaf temperature increased to a level above the predicted leaf temperature, which indicated that the stomata were gradually closing. Measurements of stomatal resistance confirmed this hypothesis. The lack of transpiration and, hence, the ceased cooling of the leaves during the treatment caused permanent damage to the leaves, which was also confirmed by a permanent reduction in sap flow rate. In conclusion, stem diameter, sap flow rate and leaf temperature measurements detected drought stress before visual symptoms were observed, so they can be implemented in an early-warning system. A combination of these plant responses gives a good overall picture of the water status of a tomato plant.

Microclimate and transpiration of a greenhouse banana crop

The interactions between a greenhouse banana crop and the surrounding environment were investigated within a large-scale type of greenhouse. This investigation took place through a whole development cycle of a mature banana crop in the region of Rabat, Morocco. Two measurement series are presented: the first from 4 to 9 March 1998 is representative of the Spring and Autumn conditions; the second which extends from 6 to 26 July 1999 is representative of the Summer period. Space- and time-dependent air evolution (the evolution of air temperature in time (time course) and space (vertically at trees levels in the greenhouse)) leaf temperature and air humidity were analysed, and evidence was provided for the significant oasis effect generated by the crop in the greenhouse. In addition, leaf area and stomatal resistance measurements are analysed and discussed. With regard to the function of microclimate-dependent parameters, a model of leaf stomatal resistance was additionally defined and developed. The transpiration model of the banana crop under cover was validated with respect to the estimated rates of heat and mass transfer implied from indoor and outdoor climatic measurements.

Development and evaluation of continuously weighing mini-lysimeters

Micrometeorological methods for measuring evapotranspiration are based on the assumption that the water vapor flux is constant with respect to height within the first few meters above the ground, and consequently are not applicable where an area is not extensively homogeneous. An increasing emphasis on energy and water flux studies in heterogeneous terrain (e.g. urban and hilly environments) has created a need to develop alternative approaches to quantify the latent heat flux. Lysimetry is an established alternative that permits the direct measurement of evapotranspiration from the ground surface and thus can provide accurate point estimates of the latent heat flux in heterogeneous environments. To date, the continuously weighing lysimeters that have been developed and extensively tested are large (surface area generally greater than 2 m 2), stationary and expensive to construct and maintain. These instruments are also inappropriate for most geographic studies of energy and water budgets in heterogeneous environments because knowledge of the spatial variability of evapotranspiration and quantification of the horizontal transport of moisture and heat require multiple, simultaneous flux determinations. This research tests two continuously weighing, portable mini-lysimeters (<0.2 m 2) designed for practical application in heterogeneous environments. The performance of the lysimeters are compared with evaporative flux measurements obtained using eddy correlation instrumentation from an extensive homogeneous surface. The soil moisture status of the monolith and the stomatal resistance of the plants within the lysimeter are compared with simultaneous measurements from the surrounding grass field. The results show that the evaporative flux, soil moisture and stomatal resistance measurements from both lysimeters compare favorably with measurements that are representative of their surroundings.

Inferring stomatal resistance of sparse crops from infrared measurements of foliage temperature

A coupled two-layer model of energy partitioning between soil and foliage for application to sparse crops was used to calculate the mean stomatal resistance from infrared measurements of foliage temperature. The model was tested against diurnal measurements of stomatal resistance, made with a diffusion porometer on two contrasting plots of wheat. One plot was kept well watered (W) and the other plot was left unwatered (D) for 40 days. Soil water deficit conditions had developed on the D plot by the time of measurement. To further test the model, a sensitivity analysis of the calculated stomatal resistance for a wide range of hypothetical leaf areas, foliage temperatures and sensible heat fluxes from the soil was conducted. At 0800 hours the foliage temperature of the W plot was 0.2°C cooler than the D plot. When measurements ceased at 1600 hours the W plot was 3.7°C cooler. As a result of these temperature differences the calculated mean leaf stomatal resistance deviated little from 90 s m −1 on the W plot but increased during the day from 130 to 250 s m −1 on the D plot. These calculated values accounted for 76% of the variance measured by porometer and were close to the 1:1 relationship. The sensitivity analysis indicated the importance of using a coupled two-layer model when calculating stomatal resistance from sparse, water stressed crops. Without such a model the effects of leaf area index on bulk boundary layer resistance and sensible heat flux from soil are ignored and the calculated stomatal resistance is overestimated. This results because drying of the soil can elevate soil surface temperature causing an increase in foliage temperature without any stomatal change.

Nitrogen Dioxide Effects on Photosynthesis in Soybean

AbstractVery little information is available on the effects of nitrogen dioxide (NO2) on photosynthesis in soybean [Glycine max (L.) Merr.]. This investigation was undertaken to study the effects of NO2 (0.0, 0.1, 0.2, 0.3, and 0.5 µL/L) on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR) of soybean cultivar Williams treated 7 h/d, for 5 d in a controlled environment. Measurements of PN, SR, and DR were made both immediately and 24 h after the termination of exposure, using a LICOR 6000 Portable Photosynthesis system. Treatment effects on PN and DR were statistically significant. Increases of 18 and 23% in PN were observed immediately following exposure to 0.2 µL/L NO2 and after a 24‐h recovery period. With the 0.5 µL/L NO2 treatment reductions in the PN of 23 and 50% were observed immediately after exposure and following the 24‐h recovery period. Dark respiration rates of leaves treated with NO2, 0.2 µL/L, were 13 and 46% higher than the control immediately after the exposure and after the 24 h recovery. Exposure to 0.2 µL/L of NO2 had a stimulating effect whereas 0.5 µL/L of NO2 inhibited photosynthesis in soybean.

Estimating the effects of understory removal from a Douglas Fir forest using a two‐layer canopy evapotranspiration model

W. J. Shuttleworth's (1979) development of the Penman‐Monteith evaporation equation for multilayer, partially wet forest canopies was modified for application to the hypostomatous canopies of Douglas fir and salal. This theory was combined with standard hourly micrometeorological measurements, eddy diffusive, boundary layer and stomatal resistance functions, and canopy and root zone water balance equations to calculate evapotranspiration rates (E) from a Douglas fir forest with salal understory over extended periods during two growing seasons. Calculated values of E agreed to within 0.2 mm d−1 of values determined using Bowen ratio‐energy balance measurements. The courses of average root zone volumetric water content (θ) calculated for two extended periods agreed well with neutron probe measurements. Salal understory removal resulted in measured values of θ being only 0.01–0.03 m3 m−3 higher over the two periods, in close agreement with calculations. This corresponded to calculated tree transpiration rates being 0.4 mm d−1 higher on average, during the second half of both periods. These higher rates were confirmed by stomatal resistance measurements.

Potato top growth as influenced by temperatures

A study was conducted to establish a growth rate response of potato plant (Solanum tuberosum L.) tops to exposure to 72-hr periods of six constant temperature treatments (10, 15, 20, 25, 30, 35°C) and to determine a thermal optimum for vegetative potato growth rates. The plants were maintained under “no stress” soil moisture conditions throughout the study. The temperature treatments were accomplished by inserting the plants into a growth chamber for 72 hours at selected temperatures. Maximum growth (as measured by percent change in leaf area) occurred at 25°C with temperature growth differences significant at the 5% level. Plant height measurements (percent change occurring during treatment time) showed maximum stem elongation at 30°C during an early growth stage and 25°C during stage 2 (4 weeks later). Predictive models developed from the data indicate maximum rates of leaf area increase in both growth stages occur at 24.7°C and that maximum rates of stem elongation occur at 31.3 and 27.4°C for growth stages 1 and 2, respectively. Leaf water potential and stomatal resistance measurements taken at the end of each treatment period indicated that no water stress occurred.

Stomatal resistance, transpiration, and growth of drought-stressed eastern cottonwood

Stomatal resistance, transpiration rate, leaf area, and height were measured on Texas clones of eastern cottonwood (Populusdeltoides Bartr. var. deltoides) grown in pots of soil maintained under three watering regimes, to determine the effect of drought on plant-water relations and growth. Leaf area expansion stopped at a stomatal resistance between 28 and 32 s cm−1. Height growth stopped at a stomatal resistance between 30 and 40 s cm−1. Transpiration rate was controlled by stomatal resistance. Stomatal resistance measurements were an easy way to determine the threshold beyond which severe moisture stress resulted in leaf and height growth cessation and eventual plant death.

Adaptation of radish Raphanus sativus L. in response to continuous exposure to ozone

A comparison was made between the development of radish Raphanus sativus L. cv. Cherry Belle in clean air and under continuous exposure to 0·17 ppm (340 μg m −3) of ozone. The area and dry weight of the individual leaves, and the dry weight of other plant organs, were determined at frequent, regular intervals throughout the experiment. Although the commercial yield of the ozone-treated plants, expressed as hypocotyl dry weight, was significantly reduced, changes in the pattern of development of these plants were observed which were of adaptive value. The pattern of assimilate distribution was altered so that new leaves were produced more rapidly in the ozone-treated plants. These later leaves were more resistant to ozone, showing a slower rate of senescence than the cotyledons or first leaves. Measurements of stomatal resistance suggested that this was an acquired, rather than an inherent, characteristic of the later leaves. By the end of the experiment, the relative growth rates in the two treatments did not differ significantly.

Predicting the canopy resistance of a mixed hardwood forest

Extensive measurements of stomatal resistance using a porometer in a maple-beech hardwood forest over two growing seasons and at two different canopy levels are described. The analysis permits a generalization that yields a final equation relating overall canopy resistance to solar irradiance and soil moisture content. Threshold irradiance initiating stomatal opening in both the maple and beech leaves was around 0.01–0.02 cal. cm −2 min −1, rising to about 0.15 cal. cm −2 min −1, when the leaves were touched by frost and senescing. Extrapolated values of minimum leaf resistance varied between 1.0 and about 7.0 sec cm −1, and were strongly dependent on soil moisture deficit. Using measured leaf area indices, overall canopy resistance was then derived from the weighted values of leaf resistance of the sunlit and shaded regions of the canopy for the whole summer season.

A Simple Diffusion Model of Transpiration Applied to a Thinned Douglas‐Fir Stand

Values of forest transpiration rate, calculated from a vapor diffusion model that uses the vapor pressure defict (v.p.d.) of the canopy air, and measurements of the stomatal resistance (every 2—3 h) and leaf area index of the canopy, agreed well with those obtained from energy balance/Bowen ratio measurements. Stomatal resistance characteristics were also used in the diffusion model instead of actual stomatal resistance measurements to calculate transpiration rate. There was reasonable agreement between these transpiration values and energy balance measurements averaged over 3—h periods. Both the model, using stomatal resistance characteristics, and energy balance measurements showed that transpiration rate increased with increasing v.p.d. until a certain v.p.d. was reached after which the rate declined. The values of v.p.d. at which maximum transpiration rate occurred were 1.5, 1.3 and 1.1 kilopascals [=15, 13 and 11 mb] for soil water potential ranges of zero to —350 kilopascals [=0 to —3.5 bars], —350 to —950 kPa [=3.5 to —9.5 bars] and —950 to —1250 kPa [=9.5 to 12.5 bars] respectively. Calculations from the model, using stomatal resistance measurements (every 2—3 h) on 7 days, indicating that the fraction of transpiration from the thinned stand transpired by the salal undergrowth during daytime ours increased from approximately 45—70% during a 4—week drying period.

A direct reading continuous flow porometer

A continuous flow porometer was designed and built: it gives a direct reading of the stomatal resistance to the diffusion of water vapour. The design, based on that of Parkinson and Legg, incorporates a new sensor and gas supply system. The porometer was tested in the laboratory against an independent measurement of stomatal resistance. This test confirmed the accuracy of stomatal resistance measurements with the porometer. In the field the porometer was used to compare the stomatal resistances of irrigated and unirrigated barley.

Water Relations of Mountain Ash (Eucalyptus regnans F. Muell.) Forests

Measurements of the vertical gradients of water potential and stomatal resistance were made in adjacent mature and regrowth forests of mountain ash to follow diurnal and seasonal behaviour. The vertical gradient of water potential at dawn in either forest was shown to be consistent with the theoretical static head of -0.1 bar m-1 but the daytime gradients in the regrowth forest were steeper (down to - 0.45 bar m-1) than in the mature forest which did not fall below -0.27 bar m-1. Stomatal resistance measurements could not be related to height but, consistent with the water potential data, the leaves of the mature forest had higher resistance to water loss than did those of the regrowth. The observations are discussed in relation to the problems of water supply to the leaves of tall trees and the possible contribution of stomatal control to the established water yield characteristics of mountain ash forests.

Corn Plant Water Stress as Influenced by Chiseling, Irrigation, and Water Table Depth1

AbstractImproved plant water status through improved soil and water management practices can result in efficient crop production and water utilization in the compact layered soils that restrict rooting in the Southeast. The effect of chiseling and irrigation on plant water status was evaluated through leaf water potential, stem diameter, and stomatal resistance measurements. Corn (Zea mays L.) was grown on a Varina sandy loam (Typic Paleudult) chiseled to 38 cm and compared with that grown on conventionally tilled plots. In 1972 chiseling had no measurable effect on the daily minimum leaf water potential under the same radiant energy level. At tasseling in 1973, with a water table 80 cm from the surface, chiseling resulted in deeper‐rooted corn that enabled utilization of water in the capillary fringe above the water table, and resulted in slightly higher (less negative) daily minimum leaf water potential, lower stomatal resistance, and smaller stem diameter fluctuations. In 1973, plant‐water status on chiseled plots was comparable with that on furrow‐irrigated plots. The cumulative effects of the small improvement in midday plant water status from chiseling resulted in a 8‐metric ton/ha increase in corn ear yields. These findings suggest chiseling of soils with root restricting layers can result in increased corn production, particularly when the water table is approximately 80 cm from the soil surface at tasseling.

Response of wheat under sub-humid irrigated conditions to atmospheric misting during grain filling

Atmospherically-induced plant water deficit and/or high temperature effects have been postulated as possible limitations to grain yield in irrigated sub-humid environments. An experiment was conducted in northwest Mexico to test this hypothesis, using a high yielding dwarf variety of wheat ( Triticum aestivum cv Yecora 70) grown under intensive irrigation. Misting during grain filling was automatically activated at ear temperatures above 25°C. Measurements of xylem water potential (ψx) and leaf relative water content (LRWC) on the control and misted areas, respectively, showed mean daily (13h30–15h30) values of 14.5 and 9.5 bars for ψx and 85.5 and 90.5% for LRWC. Stomatal resistance measurements indicated no difference between the two treatments throughout a diurnal cycle. Grain growth rate was slower in the misted treatment, apparently as a result of lower ear temperature. Treatments had no effect on final grain size and grain yield. Atmospherically-induced stress did not appear to limit grain yield under the meteorological conditions experienced during this experiment.