Relationship between stem CO₂ efflux, stem sap velocity and xylem CO₂ concentration in young loblolly pine trees

Abstract

We measured diel patterns of stem surface CO₂ efflux (E_s, mol m^-2 s^-1), sap velocity (V_s, mn s^-1) and xylem CO₂ concentration ([CO₂]) (X_s, %) in 8-year-old loblolly pine trees during the spring to determine how v, and X, influence E_s. All trees showed a strong diel hysteresis between E_s and stem temperature, where at a given temperature, E_s, was lower during the day than at night. Diel variation in temperature-independent E_s were correlated with V_s (R² = 0.54), such that at maximum v_s, E_s was reduced between 18 and 40%. However, this correlation may not represent a cause-and-effect relationship. In a subset of trees, v_s was artificially reduced by progressively removing the tree canopy. Reducing v_s to near zero had no effect on E_s and did not change the diel hysteretic response to temperature. Diel x_s tended to decrease the V_s and increase with E_s, however, in defoliated trees, large increases in X_s, when v_s = 0, had no effect on E_s. We conclude that at this time of the year, E_s, is driven primarily by respiration of cambium and phloem tissues and that sap flow and xylem transport of CO₂ had no direct influence on E_s.

Keywords

Chambers, CO2, microelectrode, granier sensors, Pinus taeda, sap flow, stem respiration

Citation

Maier, Chris A.; Clinton, Barton D. 2006. Relationship between stem CO₂ efflux, stem sap velocity and xylem CO₂ concentration in young loblolly pine trees. Plant, Cell and Environment Vol. 26: 1471-1483