Seasonal and Diurnal Patterns of Carbon Assimilation, Stomatal Conductance and Leaf Water Potential in Eucalyptus tetrodonta Saplings in a Wet - Dry Savanna in Northern Australia

1997 ◽  
Vol 45 (2) ◽  
pp. 241 ◽  
Author(s):  
L. D. Prior ◽  
D. Eamus ◽  
G. A. Duff
Keyword(s):  
Stomatal Conductance ◽  
Water Potential ◽  
Linear Relationship ◽  
Leaf Water Potential ◽  
Stomatal Closure ◽  
Carbon Assimilation ◽  
Leaf Water ◽  
Daily Maximum ◽  
Diurnal Patterns ◽  
Log Linear

Seasonal and diurnal trends in carbon assimilation, stomatal conductance and leaf water potential were studied using 1–3 m tall saplings of Eucalyptus tetrodonta (F.Muell.). The study site was in an unburnt savanna near Darwin, where rainfall is strongly seasonal. Mean daily maximum assimilation rates ranged from 14.5 µmol m-2 s-1 in May to 4.8 µmol m-2 s-1 in October. There was a linear relationship between daily maximum assimilation rates and pre-dawn leaf water potential (r = 0.62, n = 508) and a log–log linear relationship between daily maximum stomatal conductance and pre-dawn leaf water potential (r = 0.68, n = 508). Assimilation rates and stomatal conductance were always higher in the morning than in the afternoon, irrespective of season. Stomatal conductance responded more strongly to leaf-to-air vapour pressure difference when pre-dawn leaf water potentials were moderately low (–0.5 to –1.5 MPa) than when they were very low (< –1.5 MPa) or high (> –0.5 MPa). Assimilation decreased sharply when temperature exceeded 35˚C. Seasonal trends in assimilation rate could be attributed primarily to stomatal closure, but diurnal trends could not. High leaf temperatures were a major cause of lower assimilation rates in the afternoon. Approximately 90% of leaves were lost by the end of the dry season, and above-ground growth was very slow. It is hypothesised that E. tetrodonta saplings allocate most photosynthate to root and lignotuber growth in order to tolerate seasonal drought and the high frequency of fire in northern Australian savannas.

Seasonal Trends in Carbon Assimilation, Stomatal Conductance, Pre-dawn Leaf Water Potential and Growth in Terminalia ferdinandiana, a Deciduous Tree of Northern Australian Savannas

1997 ◽  
Vol 45 (1) ◽  
pp. 53 ◽  
Author(s):  
L. D. Prior ◽  
D. Eamus ◽  
G. A. Duff
Keyword(s):  
Stomatal Conductance ◽  
Water Potential ◽  
Linear Relationship ◽  
Leaf Water Potential ◽  
Dry Season ◽  
Leaf Water ◽  
Deciduous Tree ◽  
Daily Maximum ◽  
Seasonal Trends ◽  
Terminalia Ferdinandiana

Seasonal trends in pre-dawn leaf water potential and morning and afternoon rates of light-saturated assimilation and stomatal conductance were studied in saplings of the deciduous tree Terminalia ferdinandiana Excell. Mean daily maximum assimilation rates ranged from 11 µmol m-2 s-1 in the wet season to 8 µmol m-2 s-1 during the transition from the wet to the dry season. Saplings were without leaves from June to October inclusive (dry season). There was a log–linear relationship between stomatal conductance and pre-dawn leaf water potential (r = 0.76, n = 325), and a weak linear relationship between daily maximum assimilation and pre-dawn leaf water potential (r = 0.39, n = 184). Assimilation rates were higher in the morning than in the afternoon in April and May, but were similar throughout the day from December to March. Seasonal trends in assimilation could be attributed primarily to stomatal closure, but diurnal differences could not. High leaf temperatures may have been responsible for observed lower assimilation rates in the afternoon in April and May. Assimilation and stomatal conductance decreased when leaf temperatures rose above 38˚C and/or the leaf-to-air vapour pressure difference exceeded 4–4.5 kPa. Pre-dawn leaf water potentials decreased more quickly, and stomatal conductance was more sensitive to this decrease, in T. ferdinandiana saplings than in saplings of Eucalyptus tetrodonta F.Muell. a co-occurring evergreen tree. Specific leaf area and assimilation per unit dry weight were higher in T. ferdinandiana than in E. tetrodonta which is consistent with other studies of costs and benefits of deciduousness.

scholarly journals Interactions between leaf water potential, stomatal conductance and abscisic acid content of orange trees submitted to drought stress

2004 ◽  
Vol 16 (3) ◽  
pp. 155-161 ◽  
Author(s):  
Mara de Menezes de Assis Gomes ◽  
Ana Maria Magalhães Andrade Lagôa ◽  
Camilo Lázaro Medina ◽  
Eduardo Caruso Machado ◽  
Marcos Antônio Machado
Keyword(s):  
Abscisic Acid ◽  
Water Stress ◽  
Stomatal Conductance ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Acid Content ◽  
Stomatal Closure ◽  
Leaf Water ◽  
Orange Trees ◽  
Abscisic Acid Content

Thirty-month-old 'Pêra' orange trees grafted on 'Rangpur' lemon trees grown in 100 L pots were submitted to water stress by the suspension of irrigation. CO2 assimilation (A), transpiration (E) and stomatal conductance (g s) values declined from the seventh day of stress, although the leaf water potential at 6:00 a.m. (psipd) and at 2:00 p.m. (psi2) began to decline from the fifth day of water deficiency. The CO2 intercellular concentration (Ci) of water-stressed plants increased from the seventh day, reaching a maximum concentration on the day of most severe stress. The carboxylation efficiency, as revealed by the ratio A/Ci was low on this day and did not show the same values of non-stressed plants even after ten days of rewatering. After five days of rewatering only psi pd and psi2 were similar to control plants while A, E and g s were still different. When psi2 decreases, there was a trend for increasing abscisic acid (ABA) concentration in the leaves. Similarly, stomatal conductance was found to decrease as a function of decreasing psi2. ABA accumulation and stomatal closure occurred when psi2 was lower than -1.0 MPa. Water stress in 'Pera´ orange trees increased abscisic acid content with consequent stomatal closure and decreased psi2 values.

A model of stomatal closure driven by nonlinearities in soil-plant hydraulics

2021 ◽  
Author(s):  
Fabian Wankmüller ◽  
Mohsen Zarebanadkouki ◽  
Andrea Carminati
Keyword(s):  
Hydraulic Conductivity ◽  
Stomatal Conductance ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Environmental Conditions ◽  
Plant Traits ◽  
Stomatal Closure ◽  
Leaf Water ◽  
Optimization Models ◽  
Soil Conditions

&lt;p&gt;Predicting plant responses to drought is a long-standing research goal. Since stomata regulate gas-exchange between plants and the atmosphere, understanding their response to drought is fundamental. Current predictions of stomatal behavior during drought mainly rely on empirical models. These models may suit well to a specific set of plant traits and environmental growth conditions, but their predictive value is doubtful when atmospheric and soil conditions change. Stomatal optimization offers an alternative framework to predict stomatal regulation in response to drought for varying environmental conditions and plant traits. Models which apply this optimization principle posit that stomata maximize the carbon gain in relation to a penalty caused by water loss, such as xylem cavitation. Optimization models have the advantage of requiring a limited number of parameters and have been successfully used to predict stomatal response to drought for varying environmental conditions and species. However, a mechanism that enables stomata to optimally close in response to water limitations, and more precisely to a drop in the ability of the soil-plant continuum to sustain the transpiration demand, is not known. Here, we propose a model of stomatal regulation that is linked to abscisic acid (ABA) dynamics (production, degradation and transport) and that allows plants to avoid excessive drops in leaf water potential during soil drying and increasing vapor pressure deficit (VPD). The model assumes that: 1) stomatal conductance (g&lt;sub&gt;s&lt;/sub&gt;) decreases when ABA concentration close to the guard cells (C&lt;sub&gt;ABA&lt;/sub&gt;) increases; 2) C&lt;sub&gt;ABA&lt;/sub&gt; increases with decreasing leaf water potential (due to higher production); and 3) C&lt;sub&gt;ABA&lt;/sub&gt; decreases with increasing photosynthesis (e.g. due to faster degradation or transport to the phloem). Our model includes simulations of leaf water potential based on transpiration rate, soil water potential and variable hydraulic conductances of key elements (rhizosphere, root and xylem), and a function linking stomatal conductance to assimilation. It was tested for different soil properties and VPD. The model predicts that stomata close when the relation between assimilation and leaf water potential becomes nonlinear. In wet soil conditions and low VPD, when there is no water limitation, this nonlinearity is controlled by the relation between stomatal conductance and assimilation. In dry soil conditions, when the soil hydraulic conductivity limits the water supply, nonlinearity is controlled by the excessive drop of leaf water potential for increasing transpiration rates. The model predicts different relations between stomatal conductance and leaf water potential for varying soil properties and VPD. For instance, the closure of stomata is more abrupt in sandy soil, reflecting the steep decrease in hydraulic conductivity of sandy soils. In summary, our model results in an optimal behavior, in which stomatal closure avoids excessive (nonlinear) decrease in leaf water potential, similar to other stomatal optimization models. As based on ABA concentration which increases with decreasing leaf water potential but declines with assimilation, this model is a preliminary attempt to link optimization models to a physiological mechanism.&lt;/p&gt;

Stomatal Responses and Whole-Tree Hydraulic Conductivity of Orchard Macadamia integrifolia Under Irrigated and Non-Irrigated Conditions

1991 ◽  
Vol 18 (6) ◽  
pp. 661 ◽  
Author(s):  
J Lloyd ◽  
T Trochoulias ◽  
R Ensbey
Keyword(s):  
Stomatal Conductance ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Water Status ◽  
Simple Expression ◽  
Leaf Water ◽  
Leaf Water Status ◽  
Diurnal Patterns ◽  
Macadamia Integrifolia ◽  
Independent Variable

Diurnal patterns of stomatal conductance (gs) and leaf water potential (Ψ1) were determined for leaves on irrigated and non-irrigated 5-year-old Macadamia integrifolia trees over a 4-month period from September to December 1989. An empirical model for stomatal conductance was developed for irrigated trees using relationships to photon irradiance (I), leaf temperature (T1) and vapour mole fraction difference (D). This model accounted for 69% of the variance in gs, and was not improved by the inclusion of Ψ1 as an independent variable. Fitted parameters led to the effective prediction of gs for untried combinations of environmental variables. By using a simple expression to link leaf water potential to transpiration rate (E), the model was extended to prediction of Ψ1 from measurements of I, T1 and D. Stornatal conductances were significantly lower on non-irrigated trees after a 2-month dry period. Lower stornatal conductances were not accompanied by more negative Ψ1 indicating that soil rather than leaf water status may control gs in macadamia trees under non-irrigated conditions.

Photosynthesis in Coffea arabica. II. Effects of Water Stress

1980 ◽  
Vol 16 (1) ◽  
pp. 21-27 ◽  
Author(s):  
D. Kumar ◽  
Larry L. Tieszen
Keyword(s):  
Soil Moisture ◽  
Water Stress ◽  
Stomatal Conductance ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Coffea Arabica ◽  
Water Status ◽  
Stomatal Closure ◽  
Leaf Water ◽  
Plant Water

SUMMARYExperiments were carried out to relate soil moisture to leaf water potential (Ψ1), and to determine the effects of varying Ψ1, on leaf conductances and photosynthesis in coffee. Stomatal conductance was maximum at 0900 h, but plants growing in drier soil showed marked mid-day stomatal closure. After 1500 h, stomata began closing although plant water status improved. Photosynthesis in relation to changing Ψ1 appeared to exhibit roughly three different rates. At the fixed experimental temperature (25°C) low Ψ1 reduced photosynthesis throughits influence on stomata, but under field conditions low Ψ1 and an accompanying rise in temperature could lower the rate by lowering both mesophyll and stomatal conductances.

Leaf Gas Exchange and Water Relations of Lupins and Wheat. I. Shoot Responses to Soil Water Deficits

1989 ◽  
Vol 16 (5) ◽  
pp. 401 ◽  
Author(s):  
IE Henson ◽  
CR Jensen ◽  
NC Turner
Keyword(s):  
Stomatal Conductance ◽  
Water Potential ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Leaf Water Potential ◽  
Stomatal Closure ◽  
Turgor Pressure ◽  
Leaf Conductance ◽  
Leaf Water

The effects of a progressive increase in soil water deficit on the leaf conductance and gas exchange of lupin (Lupinus cosentinii) and wheat (Triticum aestivum) were investigated in pot experiments in a temperature-regulated glasshouse, using a coarse, sandy soil characteristic of the Western Australian wheatbelt. Transpiration rates decreased rapidly in both species after water was withheld, mainly as a result of stomatal closure. Photosynthesis declined also, but to a lesser extent than conductance. Leaf extension in lupin was equally as sensitive to a decrease in leaf water potential and soil water potential as stomatal conductance. Stomatal closure served to maintain the water potential of lupin leaves to within 0.1 MPa of that of control (watered) plants as the soil water content decreased from 0.14 to 0.06 m3 m-3 and as the leaf conductance and the relative transpiration rate fell to less than 50% of control values. Maintenance of leaf water potential with decreasing soil water content and stomatal conductance was less evident in wheat. In both lupin and wheat, leaf conductance decreased linearly with soil water content and curvilinearly with bulk soil matric potential, indicating that water uptake was restricted at similar water contents and matric potentials in both species. Diurnal measurements on lupin indicated a substantial reduction in stomatal conductance after water was withheld, even when the leaf water potential at midday was reduced by only 0.1 MPa and no change could be detected in the bulk leaf turgor pressure. Conductance in lupin was reduced even though the soil matric potential decreased in only part of the rooting zone. This, together with the absence of any significant change in the leaf water potential, turgor pressure, or relative water content in lupin during the initial stages of stomatal closure, suggests that a soil or root factor initiates the reduction in leaf conductance - and hence regulates the shoot water status - in response to soil drying.

Drought tolerance of clonal Malus determined from measurements of stomatal conductance and leaf water potential

2000 ◽  
Vol 20 (8) ◽  
pp. 557-563 ◽  
Author(s):  
C. J. Atkinson ◽  
M. Policarpo ◽  
A. D. Webster ◽  
G. Kingswell
Keyword(s):  
Stomatal Conductance ◽  
Drought Tolerance ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Leaf Water
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