Effects of herbivory on above- and below-ground biomass partitioning in two arid-zone dwarf shrubs

Abstract

Biomass partitioning by arid-zone dwarf shrubs between above- and below-ground fractions could be influenced by plant adaptations to herbivory. The response of potted Indigofera spinosa and I. cliffordiana to heavy and moderate top defoliations, compared to non-defoliated controls, was investigated. Relative growth rates of plants (Weeks 1–8), number of lateral shoots (Weeks 5–13), total number of leaves and leaf area (at Week 13), clipped biomass (CB) at Weeks 8 and 11 as well as residual biomass (RB), total above-ground biomass (TAGB) (i.e. the sums of CB and RB) and total root biomass (TRB) by treatments at Week 13 were greater in I. cliffordiana than in I. spinosa. Clipping reduced the shoot-root ratio (S:R) in I. cliffordiana but not in I. spinosa. For I. spinosa, plants defoliated at moderate intensities produced more root biomass (22.9%) than at heavy regimes (17.6%) or the controls (12.9%). In I. cliffordiana, below-ground biomass as a fraction of the combined biomass was less in control plants (16.5%), compared to moderate (18.2%) and heavy defoliation treatments (26.5%). The two dwarf shrub species compensated at different intensities for above- and below-ground biomass: I. spinosa at moderate defoliations and I. cliffordiana at heavy defoliations.

Keywords: biomass allocation, compensatory growth, Indigofera cliffordiana, I. spinosa, shoot:root ratio

African Journal of Range & Forage Science 2006, 23(3): 159–164