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Controls of evapotranspiration and CO2 fluxes from scots pine by surface conductance and abiotic factors.

Zha T, Li C, Kellomäki S, Peltola H, Wang KY, Zhang Y - PLoS ONE (2013)

Bottom Line: Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O)(-1) and a seasonal average of 7.06 μmol CO2 (μmol H2O)(-1).Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air.Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.

View Article: PubMed Central - PubMed

Affiliation: The School of Soil and Water Conservation, Beijing Forestry University, Beijing, China. tianshanzha@bjfu.edu.cn

ABSTRACT
Evapotranspiration (E) and CO2 flux (Fc ) in the growing season of an unusual dry year were measured continuously over a Scots pine forest in eastern Finland, by eddy covariance techniques. The aims were to gain an understanding of their biological and environmental control processes. As a result, there were obvious diurnal and seasonal changes in E, Fc , surface conductance (gc ), and decoupling coefficient (Ω), showing similar trends to those in radiation (PAR) and vapour pressure deficit (δ). The maximum mean daily values (24-h average) for E, Fc , gc , and Ω were 1.78 mmol m(-2) s(-1), -11.18 µmol m(-2) s(-1), 6.27 mm s(-1), and 0.31, respectively, with seasonal averages of 0.71 mmol m(-2) s(-1), -4.61 µmol m(-2) s(-1), 3.3 mm s(-1), and 0.16. E and Fc were controlled by combined biological and environmental variables. There was curvilinear dependence of E on gc and Fc on gc . Among the environmental variables, PAR was the most important factor having a positive linear relationship to E and curvilinear relationship to Fc , while vapour pressure deficit was the most important environmental factor affecting gc . Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O)(-1) and a seasonal average of 7.06 μmol CO2 (μmol H2O)(-1). Low Ω and its close positive relationship with gc indicate that evapotranspiration was sensitive to surface conductance. Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air. Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.

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Diurnal changes in evapotransipiration (E), CO2 flux (Fc), surface conductance (gc), decoupling coefficient (Ω), vapour pressure deficit (δ) and radiation (PAR) in a Scots pine forest ecosystem on 3 typical clear days on May 26, July 23 and September 10, 2003.
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pone-0069027-g002: Diurnal changes in evapotransipiration (E), CO2 flux (Fc), surface conductance (gc), decoupling coefficient (Ω), vapour pressure deficit (δ) and radiation (PAR) in a Scots pine forest ecosystem on 3 typical clear days on May 26, July 23 and September 10, 2003.

Mentions: There were obvious diurnal changes in evapotranspiration (E), CO2 flux (Fc, minus represents CO2 into the canopy), ecosystem surface conductance (gc), and decoupling coefficient (Ω), showing a diurnal and seasonal pattern that was marginally more similar to those of PAR than to vapour pressure deficit (δ) (Fig. 2). The values of all the variables were low at night (closer to 0 before 3 h and after 18 h) and high during the mid-day period from 8 to 16 h. The magnitudes of E, Fc, and gc were lower on September 10 than those on the other two days as a whole, showing a correspondence with PAR. Ω values were lower on May 26 than on the other two days.


Controls of evapotranspiration and CO2 fluxes from scots pine by surface conductance and abiotic factors.

Zha T, Li C, Kellomäki S, Peltola H, Wang KY, Zhang Y - PLoS ONE (2013)

Diurnal changes in evapotransipiration (E), CO2 flux (Fc), surface conductance (gc), decoupling coefficient (Ω), vapour pressure deficit (δ) and radiation (PAR) in a Scots pine forest ecosystem on 3 typical clear days on May 26, July 23 and September 10, 2003.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3722186&req=5

pone-0069027-g002: Diurnal changes in evapotransipiration (E), CO2 flux (Fc), surface conductance (gc), decoupling coefficient (Ω), vapour pressure deficit (δ) and radiation (PAR) in a Scots pine forest ecosystem on 3 typical clear days on May 26, July 23 and September 10, 2003.
Mentions: There were obvious diurnal changes in evapotranspiration (E), CO2 flux (Fc, minus represents CO2 into the canopy), ecosystem surface conductance (gc), and decoupling coefficient (Ω), showing a diurnal and seasonal pattern that was marginally more similar to those of PAR than to vapour pressure deficit (δ) (Fig. 2). The values of all the variables were low at night (closer to 0 before 3 h and after 18 h) and high during the mid-day period from 8 to 16 h. The magnitudes of E, Fc, and gc were lower on September 10 than those on the other two days as a whole, showing a correspondence with PAR. Ω values were lower on May 26 than on the other two days.

Bottom Line: Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O)(-1) and a seasonal average of 7.06 μmol CO2 (μmol H2O)(-1).Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air.Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.

View Article: PubMed Central - PubMed

Affiliation: The School of Soil and Water Conservation, Beijing Forestry University, Beijing, China. tianshanzha@bjfu.edu.cn

ABSTRACT
Evapotranspiration (E) and CO2 flux (Fc ) in the growing season of an unusual dry year were measured continuously over a Scots pine forest in eastern Finland, by eddy covariance techniques. The aims were to gain an understanding of their biological and environmental control processes. As a result, there were obvious diurnal and seasonal changes in E, Fc , surface conductance (gc ), and decoupling coefficient (Ω), showing similar trends to those in radiation (PAR) and vapour pressure deficit (δ). The maximum mean daily values (24-h average) for E, Fc , gc , and Ω were 1.78 mmol m(-2) s(-1), -11.18 µmol m(-2) s(-1), 6.27 mm s(-1), and 0.31, respectively, with seasonal averages of 0.71 mmol m(-2) s(-1), -4.61 µmol m(-2) s(-1), 3.3 mm s(-1), and 0.16. E and Fc were controlled by combined biological and environmental variables. There was curvilinear dependence of E on gc and Fc on gc . Among the environmental variables, PAR was the most important factor having a positive linear relationship to E and curvilinear relationship to Fc , while vapour pressure deficit was the most important environmental factor affecting gc . Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O)(-1) and a seasonal average of 7.06 μmol CO2 (μmol H2O)(-1). Low Ω and its close positive relationship with gc indicate that evapotranspiration was sensitive to surface conductance. Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air. Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.

Show MeSH
Related in: MedlinePlus