ALLELOPATHIC EFFECTS OF Artemisia monosperma DEL. ON GERMINATION AND SEEDLING GROWTH OF SOME RANGE PLANT SPECIES

Artemisia monosperma is observed to be as one of the first species to dominate disturbed sand dunes in Saudi Arabia. Despite its importance as a sand stabilizer, it has no forage value. It is feared that this species may arrest the natural succession of vegetation. A series of controlled environment experiments was conducted to study the potential allelopathic effects of A. monosperma on germination and seedling growth and survival of some species of sandy habitat (Lasiurus scindicus, Pennisetum divisum, Scrophularia hypericifolia, and Plantago boissieri). In one experiment, seeds were germinated in aqueous extracts prepared from leaves and inflorescence at a ratio of 1:10 weight to volume. Seeds were also germinated in a polyethylene glycol solution having an osmotic potential similar to that of extracts and in distilled water for comparison. In a second experiment, seeds were sown in 10-cm pots filled with sand and covered with a layer of 0, 1, 2 or 3g ground foliage (leaves and inflorescence) to simulate the effect of litter leachate on seedling growth and survival. In a third experiment, the effect of root exudates on seedling growth and survival was studied by irrigating recipient plants with either tap water (control) or leachates from intact one-year old A. monosperma plants grown in warm (30°C) or cool (20°C) temperatures. Results indicated that seed germination (except in S. hypericifolia) was partially controlled by the osmotic potential of extracts. The aqueous extracts were not significantly different in their effect on germination. The impact on germination ranged between 50-60% reduction in L. scindicus to a complete germination inhibition in S. hypericifolia and P. boissieri. Addition of A. monosperma litter to soil surface decreased seedling relative growth rate (RGR) and survival in proportion to the amount of litter added. Artemisia monosperma root exudates did not affect seedling biomass but reduced root to shoot ratio regardless of temperature, reduced RGR under warm temperature and decreased seedling survival especially in S. hypericifolia where complete seedling death occurred irrespective of temperature. These results have some practical importance when selecting for species in revegetation programs in A. monospermadominated sandy areas. Annals of Agric. Sc., Moshtohor, Vol. 41(4), 2003 1384