Date of Award

6-2019

Document Type

Thesis

Degree Name

Master of Science in Biology

Department

Biology

First Reader/Committee Chair

Williams, Kimberlyn

Abstract

We explored the seasonal factors that might play a role in triggering germination of Dendromecon rigidaand Ehrendorferia chrysantha.D. rigida and E. chrysantha have been found difficult to germinate using common greenhouse techniques, Keeley and Fotheringham successfully germinated both species after storing their seeds in the field over a year and treating them with smoke. Identifying the specific seasonally changing factors that stimulated germination could have implications for understanding germination requirements for these and other hard-to-germinate chaparral species.

Dendromecon rigidaand Ehrendorferia chrysanthaare part of the Papaveraceae family and both are found in the chaparral environment in Southern California. Both species are known to increase in numbers after fire events. Both are believed to have morphophysiological dormancy based on their miniscule embryo and increase in seedling presence after fire events. Climate within the chaparral environment consists of hot, dry summers and cold, wet winters.

Storing seeds of D. rigidaand E. chrysantha in the field over winter and spring months resulted in increasing germination for D. rigida seeds that were imbibed in smoke-water. Germination of D. rigidaseeds occurred within six weeks and no further germination was noted beyond that. Ehrendorferia chrysanthaseeds failed to germinate in the field.

Lab studies tested effects of stratification at different temperatures (5ºC, 10ºC, 18ºC, 25ºC and 30ºC), stratification for different durations (0, 2, 4, 8, and 12 weeks), heat-shock, and fluctuating moisture and temperature conditions on a weekly time scale, on germination of both species. Of all these treatments the only combination that was effective in germinating seeds of D. rigidaand E. chrysanthawas warm stratification at 30ºC for 8 weeks following smoke-water imbibition. Under these conditions seeds of D. rigidaand E. chrysanthagerminated to 10% and 9.3%, respectively.

Further studies on D. rigidaindicated a stratification temperature optimum between 30-40ºC with germination increasing with lack of light. These tested conditions corresponded to the daily peak soil temperatures measured at shallow depth in an area of chaparral inhabited by D. rigida. The period immediately after the first rain event after a fire may provide the chemical cues and warm stratification required to germinate buried seeds in this species.

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