Stomatal conductance, transpiration, and resistance to water uptake in a Pinussylvestris spacing experiment

1984 ◽  
Vol 14 (5) ◽  
pp. 692-700 ◽  
Author(s):  
D. Whitehead ◽  
P. G. Jarvis ◽  
R. H. Waring
Keyword(s):  
Stomatal Conductance ◽  
Hydraulic Resistance ◽  
Vapour Pressure Deficit ◽  
Water Vapour Pressure ◽  
Canopy Conductance ◽  
Cross Sectional ◽  
Summer Maximum ◽  
The Mean ◽  
Monteith Equation ◽  
Water Vapour Pressure Deficit

Stomatal conductance was measured with porometers in two plots of Pinussylvestris L. with markedly different tree spacings (plot 1, 608 stems ha−1; plot 2, 3281 stems ha−1), and hourly rates of transpiration were calculated using the Penman–Monteith equation at intervals throughout one growing season. Stomatal conductance varied little in relation to height or age of foliage. There was a linear decrease in canopy conductance with increasing water vapour pressure deficit of the air. Transpiration rates on both plots increased during the summer (maximum 0.3 mm h−1); rates on plot 1 were always lower (ca. 0.7 times) than on plot 2. Needle water potentials were similar throughout the season and only slightly lower on plot 1 than on plot 2. The mean hydraulic resistance of the trees on plot 1 was 2.4 times that on plot 2. The results support a hypothesis that considers the changes in transpiration rate, conducting cross-sectional area, canopy leaf area, water potential, and hydraulic resistance following thinning as a set of homeostatic relationships.

Processes controlling understorey evapotranspiration

1989 ◽  
Vol 324 (1223) ◽  
pp. 207-231 ◽  
Keyword(s):  
Stomatal Conductance ◽  
Forest Floor ◽  
Root Zone ◽  
Significant Proportion ◽  
Vapour Pressure Deficit ◽  
Water Vapour Pressure ◽  
Removal Experiments ◽  
Radiation Regime ◽  
Water Vapour Pressure Deficit

The understorey often accounts for a significant proportion of forest evapo- transpiration. In this paper we discuss the role of the understorey radiation regime, and the aerodynamic and stomatal conductance characteristics of the understorey in understorey evapotranspiration. Values of the McNaughton—Jarvis parameter Ω for the understorey in two mid-rotation Douglas-fir stands indicate considerable coupling between the understorey and the atmosphere above the overstorey. However, the stronger coupling between the overstorey and the atmosphere accounts for the observation that the fraction of stand evapotranspiration originating at the understorey increases as the water vapour pressure deficit increases and the soil dries. We also discuss the approaches to describing the process of evaporation from the forest floor and the results of understorey removal experiments. These show small decreases in stand evapotranspiration and root-zone soil water content, but significant increases in the transpiration and growth of the trees.

Seasonal Variation in Stomatal Responses of Two Cultivars of Lychee (Litchi chinenis Sonn)

1992 ◽  
Vol 19 (3) ◽  
pp. 317 ◽  
Author(s):  
D Batten ◽  
J Lloyd ◽  
C Mcconchie
Keyword(s):  
Stomatal Conductance ◽  
Temperature Sensitivity ◽  
Vapour Pressure Deficit ◽  
Sensitivity Coefficient ◽  
Cultivar Differences ◽  
Water Vapour Pressure ◽  
Data Sets ◽  
Diurnal Changes ◽  
Whole Plant ◽  
Significant Difference

The effect of cultivar and environment on the stomatal conductance and plant water relations of lychee (Litchi chinensis Sonn.) was investigated. Diurnal changes in stomatal conductance (gs) and leaf water potentials (Ψ1) were determined for leaves of irrigated trees of cv. 'Bengal' and cv. 'Kwai May Pink' between July and December 1990. Leaves of Bengal always had much higher gs than Kwai May Pink in winter, but as summer approached, this difference became less. Ψ1 values at midday for Bengal were always much lower than for Kwai May Pink. The linear model, E = G(Ψ1-Ψsoil), where E is transpiration rate and G is whole plant conductance, was found to be valid for nearly all the data sets collected. The values of G for Kwai May Pink were higher than for Bengal, especially in summer, and the average values of G (Bengal 4.1 and Kwai May Pink 6.3 mmol H2O m-2 s-1 Mpa-1) indicate that the lychee has a relatively efficient water transport system compared with other fruit tree species. Laboratory measurements of the responses of these cultivars confirmed observed differences in gs in the field. The responses of each cultivar to irradiance (I), leaf temperature (Tl) and leaf-air water vapour pressure deficit (D) were obtained and used to model the orchard data. The equation (see pdf) where Topt is the temperature for maximum gs, gdark is the basal gs in the dark at given T1 and D, and kI, kT and kD are constants fitted by non-linear least squares, provided an acceptable fit for both cultivars (R2 = 0.68 for Bengal and 0.55 for Kwai May Pink). The fit was not improved by including Ψ1 in the model. There was a significant difference between cultivars in kT, the temperature sensitivity coefficient. Possible implications of inter-cultivar differences in temperature sensitivity are discussed.

Regulation of canopy conductance and transpiration and their modelling in irrigated grapevines

2003 ◽  
Vol 30 (6) ◽  
pp. 689 ◽  
Author(s):  
Ping Lu ◽  
Isa A. M. Yunusa ◽  
Rob R. Walker ◽  
Warren J. Müller
Keyword(s):  
Solar Radiation ◽  
Sap Flow ◽  
Heat Dissipation ◽  
Xylem Sap ◽  
Vapour Pressure Deficit ◽  
Vitis Vinifera L ◽  
Canopy Conductance ◽  
Xylem Sap Flow ◽  
Highly Correlated ◽  
Monteith Equation

Whole-vine transpiration was estimated for well-watered nine-year-old Sultana grapevines (Vitis vinifera L. cv. Sultana) from xylem sap flow measured with Granier's heat-dissipation probes. Canopy conductance of the grapevine was calculated by inverting the Penman–Monteith equation. Transpiration from grapevine canopies was strongly controlled by the canopy conductance. Canopy conductance decreased exponentially with increasing vapour pressure deficit (VPD) except in the morning when solar radiation was less than 200 W m–2 and the canopy conductance was predominantly limited by the solar radiation. A non-linear model of canopy conductance as a function of the solar radiation and VPD explained > 90% of the variation observed in canopy conductance. Under contrasting VPD conditions (daytime maximum of 3 kPa vs 8 kPa), grapevines were able to regulate their canopy conductance from 0.006 to 0.001 m s–1 to maintain a near constant transpiration. Whole-canopy transpiration calculated from modelled canopy conductance using the Penman–Monteith equation was highly correlated with the measured transpiration (sap flow) values over the range of 0–0.20 mm h–1 (R2 > 0.85). Cross-validation shows that these mechanistic models based on solar radiation and VPD provide good predictions of canopy conductance and transpiration under the conditions of the study.

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