1. Seasonal and diel variation in xylem CO2 concentration and sap pH in sub-Mediterranean oak stems.
- Author
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Salomón, Roberto, Valbuena-Carabaña, María, González-Doncel, Inés, Gil, Luis, Rodríguez-Calcerrada, Jesús, Teskey, Robert, McGuire, Mary Anne, and Aubrey, Doug
- Subjects
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OAK , *TREE trunks , *XYLEM , *CARBON dioxide content of plants , *CIRCADIAN rhythms , *SAP (Plant) , *SEASONAL physiological variations , *PHYSIOLOGY , *PLANTS - 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 15 min 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*]. [ABSTRACT FROM AUTHOR]
- Published
- 2016
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