Temporal and spatial patterns of internal and external stem CO2 fluxes in a sub-Mediterranean oak.

To accurately estimate stem respiration (R), measurements of both carbon dioxide (CO) efflux to the atmosphere (E) and internal CO flux through xylem (F) are needed because xylem sap transports respired CO upward. However, reports of seasonal dynamics of F and E are scarce and no studies exist in Mediterranean species under drought stress conditions. Internal and external CO fluxes at three stem heights, together with radial stem growth, temperature, sap flow and shoot water potential, were measured in Quercus pyrenaica Willd.

Seasonal and diel variation in xylem CO2 concentration and sap pH in sub-Mediterranean oak stems.

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.