Secondary metabolites and nutrients of woody plants in relation to browsing intensity in African savannas

Oecologia. 2011 Dec;167(4):1063-73. doi: 10.1007/s00442-011-2042-9. Epub 2011 Jun 10.

Abstract

Carbon-based secondary metabolites (CBSMs) are assumed to function as defences that contribute to herbivore-avoidance strategies of woody plants. Severe browsing has been reported to reduce concentrations of CBSMs and increase N concentrations in individual plants, causing heavily browsed plants to be characterised by N-rich/C-poor tissues. We hypothesised that concentrations of condensed tannins (CT) and total polyphenols (TP) should decrease, or N increase, in relation to increasing intensity of browsing, rendering severely browsed plants potentially more palatable (increased N:CT) and less N-limited (increased N:P) than lightly browsed ones. We sampled naturally browsed trees (taller than 2 m) of four abundant species in southern Kruger National Park, South Africa. Species-specific relationships between N:CT, CT, TP and P concentrations and increasing browsing intensity were detected, but N and N:P were consistently invariable. We developed a conceptual post-hoc model to explain diverse species-specific CBSM responses on the basis of relative allocation of C to total C-based defence traits (e.g. spines/thorns, tough/evergreen leaves, phenolic compounds). The model suggests that species with low allocation of C to C-based defence traits become C-limited (potentially more palatable) at higher browsing intensity than species with high allocation of C to C-based defences. The model also suggests that when N availability is high, plants become C-limited at higher browsing intensity than when N availability is low.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Carbon / analysis
  • Carbon / metabolism
  • Combretaceae / chemistry
  • Combretaceae / growth & development*
  • Combretaceae / metabolism
  • Ecosystem
  • Fabaceae / chemistry
  • Fabaceae / growth & development*
  • Fabaceae / metabolism
  • Herbivory*
  • Malvaceae / chemistry
  • Malvaceae / growth & development*
  • Malvaceae / metabolism
  • Models, Biological
  • Nitrogen / analysis
  • Nitrogen / metabolism
  • Phosphorus / analysis
  • Phosphorus / metabolism
  • Plant Leaves / chemistry*
  • Plant Leaves / growth & development
  • Plant Leaves / metabolism
  • Polyphenols / analysis
  • Polyphenols / metabolism
  • South Africa
  • Tannins / analysis
  • Tannins / metabolism
  • Trees / chemistry
  • Trees / growth & development
  • Trees / metabolism

Substances

  • Polyphenols
  • Tannins
  • Phosphorus
  • Carbon
  • Nitrogen