Gas exchange processes of yellow-cedar (Chamaecyparis nootkatensis) in response to environmental variables

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Abstract

Yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) gas exchange processes were measured in response to the following primary environmental variables: photosynthetically active radiation, vapour pressure deficit, root temperature, and soil moisture. Under nonlimiting edaphic conditions, maximum stomatal conductance and maximum CO 2 assimilation increased rapidly as photosynthetically active radiation increased from 0 to 200 μmol∙m −2 ∙s −1 and from 0 to 500 μmol∙m −2 ∙s −1 , respectively. Thereafter, greater photosynthetically active radiation levels only resulted in minor increases in stomatal conductance and CO 2 assimilation. Maximum stomatal conductance and maximum CO 2 assimilation declined in a concave manner as vapour pressure deficit increased from 1 to 5 kPa. Response surface model for stomatal conductance showed vapour pressure deficit was the primary influence after light had caused initial stomatal opening. Response surface modeling approach showed CO 2 assimilation increased as photosynthetically active radiation increased, but increased vapour pressure deficit resulted in a suppression of CO 2 assimilation. Response surface model showed internal CO 2 concentration declined sharply as photosynthetically active radiation increased from 0 to 500 μmol∙m −2 ∙s −1 , but it remained constant with increasing vapour pressure deficit. Decreasing root temperature resulted in a continual decline in CO 2 assimilation and stomatal conductance from 22 to 1 °C, while internal CO 2 concentration declined from 22 to 13 °C with little change between 13 and 1 °C. As predawn shoot water potential decreased from −0.5 to −2.0 MPa, CO 2 assimilation declined in a linear manner, while stomatal conductance and internal CO 2 concentration declined in a concave manner. Key words: Chamaecyparis nootkatensis, CO 2 assimilation, stomatal conductance, internal CO 2 concentration, photosynthetically active radiation, vapour pressure deficit, root temperature, predawn shoot water potential.

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