Species and population-level variation in germination strategies of cold desert forbs

Background/Question/Methods

Many desert plants have some degree of seed dormancy. Explanations for this common life history strategy include the ability to persist during unfavorable environmental conditions, the reduction of seedling competition, and maximizing fitness through higher precision in the timing of germination. Seed dormancy affects the seasonal timing of germination for many plants, thus determining when and with whom they will compete for resources. Therefore, the evolution of seed dormancy is potentially related to the level of environmental variability a species or population experiences, range size or average dispersal distance, and interactions with other species.

This experiment investigates the germination ecology of ten Great Basin forb species, with the intention of understanding a) their optimal germination conditions, and how these relate to their temporal and spatial presence on the landscape, and b) variation within species in germination cues. Seeds were collected from 2-3 populations per species during the spring and summer of 2013. Factorial seed treatments varied after-ripening temperatures (either room temperature or 40°C) and exposure to wet, cold conditions (2°C for 0, 2, 4, or 6 weeks) before placement in a moderate (15°C) temperature. These treatments were designed to determine if seeds require warm or cold temperatures to break dormancy.

Results/Conclusions

We found both species level and population level differences in germination strategies. In general, of the 10 species investigated, 4 germinated immediately, regardless of pre-treatment, 2 showed response to short cold treatments, and 4 are showing responses to longer treatments, though as noted, there was considerable variation among populations for even these broad patterns.  Overall, approximately 35% of seeds germinated at 2°C within the first 3 weeks of the study, indicating the potential for fall germination in this suite of species.

There is increasing interest in restoration of forbs in the Great Basin. Because of high variance in the timing and amount of annual precipitation in the Great Basin, understanding germination strategies is important for designing restoration mixes, as the ideal mix would include species with contrasting strategies in order to maximize the chance of seedling establishment in a given year. Knowledge about species-specific germination preferences will help managers choose native forbs for incorporation into restoration protocols.  This research will also identify species that possess high levels of seed dormancy, which can be undesirable in restoration if dormancy prevents seedling establishment over management time scales.