Southern Research Station

Title: Physiological girdling of pine trees via phloem chilling: proof of concept

Author: Johnsen, Kurt; Maier, Chris; Sanchez, Felipe; Anderson, Peter; Butnor, John; Waring, Richard; Linder, Sune

Date: 2007

Source: Plant, Cell and Environment, Vol. 30: 128-134

Description: Quantifying below-ground carbon (C) allocation is particularly difficult as methods usually disturb the root– mycorrhizal–soil continuum. We reduced C allocation below ground of loblolly pine trees by: (1) physically girdling trees and (2) physiologically girdling pine trees by chilling the phloem. Chilling reduced cambium temperatures by approximately 18 °C. Both methods rapidly reduced soil CO₂ efflux, and after approximately 10 days decreased net photosynthesis (Pn), the latter indicating feedback inhibition. Chilling decreased soil-soluble C, indicating that decreased soil CO₂ efflux may have been mediated by a decrease in root C exudation that was rapidly respired by microbes. These effects were only observed in late summer/early autumn when above-ground growth was minimal, and not in the spring when above-ground growth was rapid. All of the effects were rapidly reversed when chilling was ceased. In fertilized plots, both chilling and physical girdling methods reduced soil CO₂ efflux by approximately 8%. Physical girdling reduced soil CO₂ efflux by 26% in non-fertilized plots. This work demonstrates that phloem chilling provides a non-destructive alternative to reducing the movement of recent photosynthate below the point of chilling to estimate C allocation below ground on large trees.

Keywords: allocation, below ground, carbon, chilling, feedback inhibition, non-destructive, respiration, root exudation, soluble c.

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Citation

Johnsen, Kurt; Maier, Chris; Sanchez, Felipe; Anderson, Peter; Butnor, John; Waring, Richard; Linder, Sune  2007.  Physiological girdling of pine trees via phloem chilling: proof of concept.   Plant, Cell and Environment, Vol. 30: 128-134