title: Seasonal and diel variation in xylem CO2 concentration and sap pH in sub-Mediterranean oak stems.
abstract: Since a substantial portion of respired CO2 remains within the stem, diel and seasonal trends in stem CO2 concentration ([CO2]) are of major interest in plant respiration and carbon budget research. However, continuous long-term stem [CO2] studies are scarce, and generally absent in Mediterranean climates. In this study, stem [CO2] was monitored every 15min together with stem and air temperature, sap flow, and soil water storage during a growing season in 16 stems of Quercus pyrenaica to elucidate the main drivers of stem [CO2] at different temporal scales. Fluctuations in sap pH were also assessed during two growing seasons to evaluate potential errors in estimates of the concentration of CO2 dissolved in xylem sap ([CO2*]) calculated using Henry's law. Stem temperature was the best predictor of stem [CO2] and explained more than 90% and 50% of the variability in stem [CO2] at diel and seasonal scales, respectively. Under dry conditions, soil water storage was the main driver of stem [CO2]. Likewise, the first rains after summer drought caused intense stem [CO2] pulses, suggesting enhanced stem and root respiration and increased resistance to radial CO2 diffusion. Sap flow played a secondary role in controlling stem [CO2] variations. We observed night-time sap pH acidification and progressive seasonal alkalinization. Thus, if the annual mean value of sap pH (measured at midday) was assumed to be constant, night-time sap [CO2*] was substantially overestimated (40%), and spring and autumn sap [CO2*] were misestimated by 25%. This work highlights that diel and seasonal variations in temperature, tree water availability, and sap pH substantially affect xylem [CO2] and sap [CO2*].
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
authors.initials: R
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: Warnell School of Forestry and Natural Resources, University of Georgia, 180 East Green St, Athens, GA 30602-2152, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Teskey
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 Savannah River Ecology Lab, University of Georgia, Drawer E, Aiken, SC 29802, USA.
authors.forename: Doug
authors.initials: D
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.
authors.forename: Luis
authors.initials: L
authors.lastname: Gil
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 / Q000032:analysis* / Q000378:metabolism; D002940:Circadian Rhythm; D006863:Hydrogen-Ion Concentration; D018547:Plant Stems / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D029963:Quercus / Q000378:metabolism* / Q000502:physiology; D012621:Seasons; D013696:Temperature; D014197:Trees / Q000378:metabolism / Q000502:physiology; D052584:Xylem / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology
chemical_list: D002245:Carbon Dioxide
keywords: Oak (Quercus pyrenaica); sap [CO2] misestimation; sap pH; seasonal variation; stem respiration; summer drought; xylem CO2 transport.