title: Secondary metabolites and nutrients of woody plants in relation to browsing intensity in African savannas.
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.
authors.affiliation: Department of Agriculture, University of Zululand, KwaDlangezwa, South Africa. pscoging@pan.uzulu.ac.za
authors.forename: Peter F
authors.initials: PF
authors.lastname: Scogings
authors.forename: Joakim
authors.initials: J
authors.lastname: Hjältén
authors.forename: Christina
authors.initials: C
authors.lastname: Skarpe
mesh_terms: D002244:Carbon / Q000032:analysis / Q000378:metabolism; D029764:Combretaceae / Q000737:chemistry / Q000254:growth & development* / Q000378:metabolism; D017753:Ecosystem; D007887:Fabaceae / Q000737:chemistry / Q000254:growth & development* / Q000378:metabolism; D060434:Herbivory; D019660:Malvaceae / Q000737:chemistry / Q000254:growth & development* / Q000378:metabolism; D008954:Models, Biological; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry* / Q000254:growth & development / Q000378:metabolism; D059808:Polyphenols / Q000032:analysis / Q000378:metabolism; D013019:South Africa; D013634:Tannins / Q000032:analysis / Q000378:metabolism; D014197:Trees / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism
chemical_list: D059808:Polyphenols; D013634:Tannins; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen