Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Doctorat → États-Unis → 1989 → Responses of an African dwarf shrub, Indigofera Spinosa, to competition, water stress, and defoliation

Colorado State University (1989)

Responses of an African dwarf shrub, Indigofera Spinosa, to competition, water stress, and defoliation

Mugambi, Mworia

Titre : Responses of an African dwarf shrub, Indigofera Spinosa, to competition, water stress, and defoliation.

Auteur : Mugambi, Mworia

Université de soutenance : Colorado State University, USA

Grade : Doctor of Philosophy (PhD) 1989

Résumé
Indigofera spinosa, a dwarf shrub that is widely distributed in arid areas of northern Kenya, tolerates heavy defoliation and drought. The goal of these experiments was to study the responses of I. spinosa to water stress, defoliation and competition with grasses under a relatively controlled (garden) situation and in a natural setting. In the garden experiment, defoliation had no effect on total aboveground biomass produced or total nitrogen yield, but watering at 15 day intervals reduced both biomass and nitrogen yield. Allocation of both biomass and nitrogen to leaves was increased by defoliation, while allocation to stems was reduced. Root biomass was reduced by heavy defoliation at the 5 day watering frequency, but not at 10-or 15-day watering intervals. Allocation of biomass and nitrogen to grazers, as a proportion of the total yield, was not affected by watering frequency. A field experiment in a mature stand of I. spinosa was conducted to evaluate the effects of defoliation and competition with grasses on aboveground production, nitrogen yield, and xylem water potential. Competition had a strong influence on all the measured variables, while defoliation had less of an impact. Plants under reduced competition had greater yields of biomass and nitrogen (by more than 200%) than plants under full competition. Defoliation reduced allocation to residual biomass and increased allocation of biomass to grazers. Seasonal trends in maximum (predawn) and minimum (midday) xylem water potentials of I. spinosa showed few systematic differences among plants that received different treatments when there was adequate soil moisture (late April through mid June). During periods of severe drought, I. spinosa plants under reduced competition with grasses had significantly higher xylem water potentials than plants that experienced full competition. Defoliation of I. spinosa, however, continued to have little effect on water potential.

Mots Clés : Range management / Grasslands / Indigofera spinosa / Deserts

Présentation

Page publiée le 22 septembre 2010, mise à jour le 18 novembre 2018