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

Gas exchange processes of yellow-cedar (Chamaecyparis nootkatensis) in response to environmental variables STEVENC. GROSSNICKLE British Columbia Research Corporation, Forest Biotechnology Centre, 3650 Wesbrook Malj, Vancouver, B.C., Canada V6S 2L2 AND

JOHNH. RUSSELL

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British Columbia Ministry of Forests, Cowichan Lake Research Station, Box 335, Mesachie Lake, B.C., Canada VOR 2N0 Received February 4 , 1991 GROSSNICKLE, S. C., and RUSSELL,J. H. 1991. Gas exchange processes of yellow-cedar (Chamaecyparis nootkatensis) in response to environmental variables. Can. J. Bot. 69: 2684-2691. 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, assimilation increased rapidly as photosynthetically active radiation increased from 0 to 200 p m ~ l . m - ~ . s - ' and from 0 to 500 p m ~ l . m - ~ . sI,- respectively. Thereafter, greater photosynthetically active radiation levels only resulted in minor increases in stomatal conductance and CO, assimilation. Maximum stomatal conductance and maximum CO, assimilation declined in a concave manner as vapour pressure deficit increased from 1 to 5 kPa. Response surface model for stomata1 conductance showed vapour pressure deficit was the primary influence after light had caused initial stomatal opening. Response surface modeling approach showed CO, assimilation increased as photosynthetically active radiation increased, but increased vapour pressure deficit resulted in a suppression of CO, assimilation. Response surface model showed internal CO, concentration declined sharply as photosynthetically active radiation increased from 0 to 500 p m ~ l . m - ~ . s - 'but , it remained constant with increasing vapour pressure deficit. Decreasing root temperature resulted in a continual decline in CO, assimilation and stomatal conductance from 22 to 1°C, while internal CO, 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, assimilation declined in a linear manner, while stomatal conductance and internal CO, concentration declined in a concave manner. Key words: Chamaecyparis nootkatensis, CO, assimilation, stomatal conductance, internal C0, concentration, photosynthetically active radiation, vapour pressure deficit, root temperature, predawn shoot water potential. GROSSNICKLE, S. C., et RUSSELL,J. H. 1991. Gas exchange processes of yellow-cedar (Chamaecyparis nootkatensis) in response to environmental variables. Can. J. Bot. 69 : 2684-2691. Les auteurs ont mesure les Cchanges gazeux du Chamaecyparis nootkatensis (D. Don) Spach en rCaction aux variables primaires du milieu : radiations actives sur la photosynthkse, deficit de pression de vapeur, temperature racinaire et humidit6 du sol. Sous des conditions Cdaphiques non-limitatives, la conductance stomatale maximale et I'assimilation maximum du CO, augmentent rapidement B mesure que la radiation photosynthCtiquement active passe de 0 a 200 pmol.m-'.s-' et de 0 a 500 pmol.rn-'.s-l, respectivement. Par aprks l'augmentation des niveaux de radiation photosynthCtiquement active n'entraine qu'une faible augmentation de la conductance stomatale et de l'assimilation du COY La conductance stomatale et l'assimilation du CO, maximales diminuent de f a ~ o nconcave a mesure que le dCficit de pression de vapeur agumente de 1 a 5 kPa. Un modkle de rCaction de surface pour la conductance stomatale montre que le dkficit de pression de vapeur devient le facteur determinant aprks que la lumikre ait declenchk l'ouverture initiale des stomates. La mithode de modClisation des rkactions de surface montre que I'assimilation du CO, s'accroit i mesure que la radiation photosynthetiquement active augmente, mais I'augmentation du deficit de pression de vapeur entraine une suppression de I'assimilation du COZ. Le modkle de rkaction de surface montre que la concentration interne de CO, diminuent fortement lorsque la radiation photosynthCtiquement active passe de 0 ii 500 pmol.m-'.s-l, mais demeure constante avec une augmentation du deficit de pression de vapeur. Une diminution de la temperature racinaire entraine une diminution continue de l'assimilation du CO, et de la conductance stomatale entre 22 et l0C