Seeds from 30 species of grasses and forbs native to Pacific Northwest prairies were tested for physical and physiological dormancy. The physical dormancy was determined by mechanically and chemically scarifying seeds. Physiological dormancy was evaluated with cold stratification before germination. Experiments were analyzed individually with ANOVA analysis, and by seed lots through time using multiple regression. Three of the tested species had too little germination to determine what kind of dormancy was present. Physical dormancy was found in three legumes that required a treatment to break the hard seed coat. These species, Lotus unifoliolatus, Lupinus albicaulis, and Trifolium willdenovii also had increased germination following cold stratification. This can be taken as evidence of physiological dormancy. Physiological and physical dormancy together is considered combinational dormancy. Another eight species had increased germination after cold stratification. This included both species that did not germinate without cold stratification (Aquilegia formosa, Camassia leichtlinii, C. quamash, Heracleum maximum, Lomatium nudicaule, Perideridia oregona, and Sidalcea campestris), and species with germination proportions that increased following stratification (Eriophyllum lanatum, and the legumes). Four annual forbs (Clarkia purpurea, Collomia grandiflora, Gilia capitata, and Madia gracilis) had increased germination when seeds were cold stratified, but the response was more consistent with a low temperature requirement for germination than physiological dormancy. The remaining 12 species germinated with no pretreatments. Understanding the germination requirements of these species will aid in their propagation for restoration and the provisioning of ecosystem services and may help explain the ecology of these species on the landscape.
For more articles from the Spring 2011 issue of Northwest Science please refer to the link below: