title: Temporal and spatial patterns of internal and external stem CO2 fluxes in a sub-Mediterranean oak.
abstract: To accurately estimate stem respiration (RS), measurements of both carbon dioxide (CO2) efflux to the atmosphere (EA) and internal CO2flux through xylem (FT) are needed because xylem sap transports respired CO2upward. However, reports of seasonal dynamics of FTand EAare scarce and no studies exist in Mediterranean species under drought stress conditions. Internal and external CO2fluxes at three stem heights, together with radial stem growth, temperature, sap flow and shoot water potential, were measured in Quercus pyrenaica Willd. in four measurement campaigns during one growing season. Substantial daytime depressions in temperature-normalized EAwere observed throughout the experiment, including prior to budburst, indicating that diel hysteresis between stem temperature and EAcannot be uniquely ascribed to diversion of CO2in the transpiration stream. Low internal [CO2] (<0.5%) resulted in low contributions of FTto RSthroughout the growing season, and RSwas mainly explained by EA(>90%). Internal [CO2] was found to vary vertically along the stems. Seasonality in resistance to radial CO2diffusion was related to shoot water potential. The low internal [CO2] and FTobserved in our study may result from the downregulation of xylem respiration in response to a legacy of coppicing as well as high radial diffusion of CO2through cambium, phloem and bark tissues, which was related to low water content of stems. Long-term studies analyzing temporal and spatial variation in internal and external CO2fluxes and their interactions are needed to mechanistically understand and model respiration of woody tissues.
authors.affiliation: Forest Genetics and Ecophysiology Research Group, E.T.S. Forestry Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
authors.forename: Roberto L
authors.initials: RL
authors.lastname: Salomón
authors.affiliation: Forest Genetics and Ecophysiology Research Group, E.T.S. Forestry Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Valbuena-Carabaña
authors.affiliation: Forest Genetics and Ecophysiology Research Group, E.T.S. Forestry Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Gil
authors.affiliation: Warnell School of Forestry and Natural Resources, University of Georgia, 180 East Green St, Athens, GA 30602-2152, USA.
authors.forename: Mary Anne
authors.initials: MA
authors.lastname: McGuire
authors.affiliation: Warnell School of Forestry and Natural Resources, University of Georgia, 180 East Green St, Athens, GA 30602-2152, USA.
authors.forename: Robert O
authors.initials: RO
authors.lastname: Teskey
authors.affiliation: Warnell School of Forestry and Natural Resources, University of Georgia, 180 East Green St, Athens, GA 30602-2152, USA.|Savannah River Ecology Lab, University of Georgia, Drawer E, Aiken, SC 29802, USA.
authors.forename: Doug P
authors.initials: DP
authors.lastname: Aubrey
authors.affiliation: Forest Genetics and Ecophysiology Research Group, E.T.S. Forestry Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain.
authors.forename: Inés
authors.initials: I
authors.lastname: González-Doncel
authors.affiliation: Forest Genetics and Ecophysiology Research Group, E.T.S. Forestry Engineering, Technical University of Madrid, Ciudad Universitaria s/n, 28040 Madrid, Spain jesus.rcalcerrada@upm.es.
authors.forename: Jesús
authors.initials: J
authors.lastname: Rodríguez-Calcerrada
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D018547:Plant Stems / Q000378:metabolism*; D029963:Quercus / Q000378:metabolism*; D013030:Spain; D014197:Trees / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide
keywords: carbon balance; carbon loss; daytime CO2 depression; forest decline; seasonal variation; stem CO2 efflux; summer drought; xylem CO2 transport