Leaf chemistry of woody plants in relation to season, canopy retention and goat browsing in a semiarid subtropical savanna

Scogings, Peter F., Dziba, Luthando E., and Gordon, Iain J. (2004) Leaf chemistry of woody plants in relation to season, canopy retention and goat browsing in a semiarid subtropical savanna. Austral Ecology, 29 (3). pp. 278-286.

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It is assumed that the phytochemistry of browse species protects their biomass and nutrients against herbivory. In this study we were primarily interested in (i) seasonal and phenology-related variations in leaf chemistry, and (ii) chemistry-related variations in the feeding behaviour of domestic goats. Such knowledge would guide management-orientated modelling of browse-browser interactions in seasonal, subtropical zones where goats are abundant. The browse species studied were typical of semiarid savannas in southern Africa: Grewia occidentalis L. (Tiliaceae), Scutia myrtina (Burm. f) Kurz (Rhamnaceae), Diospyros lycioides Desf. ssp. lycioides (Ebenaceae), Rhus longispina Eckl. and Zeyh. (Anacardiaceae), Ehretia rigida (Thunb.) Druce (Boraginaceae) and Acacia karroo Hayne (Mimosoideae). Nitrogen (N), phosphorus (P), condensed tannins (CT), protein-precipitating tannins (PPT), total phenols (TP), cellulose and lignin concentrations were estimated for each species during the late dormant and early growing seasons. N, P, CT and TP were elevated during the growth season, while cellulose, lignin and PPT decreased. Unlike cytoplasm contents, which varied seasonally, cell wall and vacuole contents varied both seasonally and among species. Except that seasonal variation in N of deciduous species was greater than that of evergreen species, leaf phenology was not related to variations in forage quality. Short-term intake rates were not related to primary metabolite concentrations, but were positively related to secondary metabolites. Elevated intake rates of putative defences were concluded to be side-effects of attempts by goats to increase nutrient intake rate, indicating tolerance of chemical defences. Without support for the hypothesis that chemical defences are correlated to canopy retention, we propose an alternative hypothesis, that defences are distributed among woody plants in semiarid, subtropical savannas according to shoot morphology because it affects the vulnerability of plant parts to browsers.

Item ID: 42559
Item Type: Article (Research - C1)
ISSN: 1442-9993
Keywords: consumption rate, optimal defence, plant defence, resource availability, southern Africa
Funders: National Research Foundation, South Africa, Royal Society of London (RS)
Date Deposited: 10 Feb 2016 07:43
FoR Codes: 06 BIOLOGICAL SCIENCES > 0601 Biochemistry and Cell Biology > 060199 Biochemistry and Cell Biology not elsewhere classified @ 50%
05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050199 Ecological Applications not elsewhere classified @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970105 Expanding Knowledge in the Environmental Sciences @ 100%
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