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

Abstract

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.

  • 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
  • Keywords: allocation, below ground, carbon, chilling, feedback inhibition, non-destructive, respiration, root exudation, soluble c.
  • Posted Date: December 4, 2006
  • Modified Date: December 13, 2006
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