Trees

, Volume 20, Issue 6, pp 725–733

Effects of leaf and branch removal on carbon assimilation and stem wood density of Eucalyptus grandis seedlings

Original Article

DOI: 10.1007/s00468-006-0087-x

Cite this article as:
Thomas, D.S., Montagu, K.D. & Conroy, J.P. Trees (2006) 20: 725. doi:10.1007/s00468-006-0087-x
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Abstract

The rate of leaf CO2 assimilation (Al) and leaf area determine the rate of canopy CO2 assimilation (Ac) can be thought proportional to assimilate supply for growth and structural requirements of plants. Partitioning of biomass within plants and anatomy of cells within stems can determine how assimilate supply affects both stem growth and wood density. We examined the response of stem growth and wood density to reduced assimilate supply by pruning leaf area. Removing 42% of the leaf area of Eucalyptus grandis Hill ex Maiden seedlings did not stimulate leaf-level photosynthesis (Al) or stomatal conductance, contrary to some previous studies. Canopy-level photosynthesis (Ac) was reduced by 41% immediately after pruning but due almost solely to continued production of leaves, and was only 21% lower 3 weeks later. Pruning consequently reduced seedling biomass by 24% and stem biomass by 18%. These reductions in biomass were correlated with reduced Ac. Pruning had no effect on stem height or diameter and reduced wood density to 338 kg m−3 compared to 366 kg m−3 in control seedlings. The lower wood density in pruned seedlings was associated with a 10% reduction in the thickness of fibre cell walls, and as fibre cell diameter was invariant to pruning, this resulted in smaller lumen diameters. These anatomical changes increased the ratio of cross-sectional area of lumen to area cell wall material within the wood. The results suggest changes to wood density following pruning of young eucalypt trees may be independent of tree volume and of longer duration.

Keywords

Defoliation Eucalypt Fibre cell wall Photosynthesis Pruning Stomatal conductance 

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • D. S. Thomas
    • 1
    • 3
  • K. D. Montagu
    • 2
    • 4
  • J. P. Conroy
    • 1
  1. 1.Centre for Horticulture and Plant SciencesUniversity of Western SydneySouth PenrithAustralia
  2. 2.Research and Development DivisionState Forests of NSWBeecroftAustralia
  3. 3.Forests NSW, Land Management and Technical ServicesCoffs Harbour JettyAustralia
  4. 4.Cooperative Research Centre for Irrigation FuturesSchool of Environment and Agriculture, University of Western SydneySouth PenrithAustralia

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