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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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Parameters for the linear regressions between evapotranspiration (E) and surface conductance (gc), air temperature (T), vapour pressure deficit (δ), and radiation (PAR) at given times from 6 to 18 h throughout the growing season.The regression values are calculated on the basis of a dry surface (PAR >200 µmol m−2 s−1, with zero precipitation above and under the canopy).
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pone-0069027-g006: Parameters for the linear regressions between evapotranspiration (E) and surface conductance (gc), air temperature (T), vapour pressure deficit (δ), and radiation (PAR) at given times from 6 to 18 h throughout the growing season.The regression values are calculated on the basis of a dry surface (PAR >200 µmol m−2 s−1, with zero precipitation above and under the canopy).

Mentions: In order to examine the daily variations in the sensitivity of E to the variables (PAR, gc, δ, and T) and variations in their relationship, we plot the slopes, intercepts and R-square of their regression lines over the growing season. As a result, the values of the slopes for the linear regression between E and gc, T, δ, and PAR were higher in the morning, from 8 to 11 h, than in the afternoon, after 12 h (Fig. 6). Similarly, R-square exhibited higher values in the morning than in the afternoon, from 8 to 11 h. The high values for the intercept occurred after 11 h.


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)

Parameters for the linear regressions between evapotranspiration (E) and surface conductance (gc), air temperature (T), vapour pressure deficit (δ), and radiation (PAR) at given times from 6 to 18 h throughout the growing season.The regression values are calculated on the basis of a dry surface (PAR >200 µmol m−2 s−1, with zero precipitation above and under the canopy).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0069027-g006: Parameters for the linear regressions between evapotranspiration (E) and surface conductance (gc), air temperature (T), vapour pressure deficit (δ), and radiation (PAR) at given times from 6 to 18 h throughout the growing season.The regression values are calculated on the basis of a dry surface (PAR >200 µmol m−2 s−1, with zero precipitation above and under the canopy).
Mentions: In order to examine the daily variations in the sensitivity of E to the variables (PAR, gc, δ, and T) and variations in their relationship, we plot the slopes, intercepts and R-square of their regression lines over the growing season. As a result, the values of the slopes for the linear regression between E and gc, T, δ, and PAR were higher in the morning, from 8 to 11 h, than in the afternoon, after 12 h (Fig. 6). Similarly, R-square exhibited higher values in the morning than in the afternoon, from 8 to 11 h. The high values for the intercept occurred after 11 h.

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