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Accueil du site → Doctorat → États-Unis → 1992 → Germination and seedling establishment of spiny hopsage (Grayia spinosa [Hook.] Moq.)

Oregon State University (1992)

Germination and seedling establishment of spiny hopsage (Grayia spinosa [Hook.] Moq.)

Shaw, Nancy Lynn

Titre : Germination and seedling establishment of spiny hopsage (Grayia spinosa [Hook.] Moq.)

Auteur : Shaw, Nancy Lynn

Université de soutenance : Oregon State University

Grade : Doctor of Philosophy (PhD) 1992

Résumé
Reestablishment of spiny hopsage (Grayia spinosa (Hook.) Moq.) where depleted or lost on shrub steppe sites can improve forage, plant cover, and soil stabilization. The objectives of this study were to : (1) determine direct-seeding requirements ; (2) develop optimum germination pretreatments ; and (3) examine dormancy mechanisms in spiny hopsage fruits and seeds. The effects of seed source, planting date, and site preparation method on seed germination and seedling establishment (SE) were examined at Birds of Prey and Reynolds Creek in southwestern Idaho. Three seed sources were planted on rough or compact seedbeds on 4 dates in 1986-87 and 3 dates in 1987-88. Exposure to cool-moist environments improved spring SE from early fall (EF) and late fall (LF) plantings. Few seedlings emerged from early (ESp) or late spring (LSp) plantings. SE was low at 1 site in 1986-87 and at both sites in 1987-88, probably due to lack of precipitation. For the successful 1986-87 planting, seedling density was greater on rough compared to compact seedbeds in April and May, possibly due to improve microclimate conditions. Growth rate varied among seed sources, but seedlings developed a deep taproot (mean length 266 mm) with few lateral roots the first season. Seeds were planted on 3 dates in 1986-87 and 1987-88, and nylon bags containing seeds were planted on 4 dates each year to study microenvironment effects on germination (G), germination rate (GR), and SE. Bags were recovered on subsequent planting dates, and seeds were tested for moisture content, viability, G, and GR. In 1987-88 with low precipitation, seedlings established only from LF plantings ($<$1/m$\sp2$). In response to high March 1989 precipitation, establishment was 6 and 26 times greater on LF compared to ESp plantings. Incubating seed in soil from LF to ESp 1987-88 increased G 6-11 times and GR 12 and 13 days. Incubating seeds in soil from W to ESp increased G 1-6 times and GR 4 and 8 days compared to controls. In 1988-89, incubation from LF to W increased G 17 times and GR 10 and 11 days compared to controls, while incubation from W to ESp increased G 4 and 7 times and GR 10 and 11 days. Utricles and seeds responded to stratification for 60 days at 3-5$\sp\circ$C. Mean G at 5/15$\sp\circ$C (44%) was similar to maximum constant temperature G obtained over the 20-30$\sp\circ$C (37-40%). Embryo excision and mechanical scarification released dormancy imposed by the elastic inner layers of the testa. Moist heat at 35$\sp\circ$C reduced dormancy ; the effect was greater for seeds than utricles. Dormancy imposed by bracts was not reduced by leaching. Bracts did not inhibit water uptake or provide mechanical restraint to the radicle ; they may act by reducing permeability to oxygen or other gases.

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