Germination and Growth of Some Semidesert Grassland Species Treated with Aqueous Extract from Creosotebush

Abstract

The effects of aqueous extracts from creosotebush (Larrea tridentata) material on germination and initial growth of black grama (Boutelous eriopoda), bush muhly (Muhlenbergia porteri), and creosotebush were studied. There was no apparent difference among extracts obtained from the various creosotebush plant parts. An aqueous extract from leaves and twigs significantly reduced germination of black grama caryopses, but the germination of bush muhly caryopses and of creosotebush seeds (removed from the carpels) was not affected. Less concentrated extracts did not significantly reduce germination of test species. However, radicle and plumule growth of black grama and bush muhly were significantly reduced by all extracts. Apparently the relatively low osmotic concentrations or the moderate pH's were not responsible for these reductions in growth. Comparison among creosotebush seeds (removed from the carpel) watered with a carpel extract and a water—mannitol solution of the same osmotic concentration, and carpels treated with water indicated that there is a structural characteristic or a non—water—soluble chemical compound in the carpel which inhibits germination of creosotebush. Germination of creosotebush seeds treated with water—mannitol solutions of 1.50, 3.50, 5.00, and 7.00 atm osmotic concentration was significantly reduced as compared to those treated with low concentrations simulating field capacity. Nutrient solution recycled for 37 days around the roots of creosotebush plants growing in a gravel—sand substratum was not inhibitory to germination or initial growth. In a pot test, creosotebush extracts created a crust on the soil surface which reduced the infiltration rate of water. Some of the preceding factors may possibly contribute to the degeneration of grassland areas where creosotebush is present.