Variation in the onset of first rains reveals germination niche specialists and generalists in a clade of native jewelflowers

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Arquel Miller, Sarah Ashlock, Eda Ceviker, Jennifer R. Gremer and Johanna Schmitt, Evolution and Ecology, University of California, Davis, Davis, CA, Sharon Strauss, Department of Evolution and Ecology, University of California, Davis, Davis, CA

Background/Question/Methods
Germination timing is crucial for plants. Seeds use environmental factors like temperature, day length, and soil moisture to time germination. Responses to these cues construct the germination niche- the range of seasonal conditions under which germination can occur. Mismatches in timing and conditions can negatively affect establishment and reproduction, and may be more frequent under climate change. To understand how plant populations will respond to climate change, it is critical to understand the germination niche. In this experiment, we explored how different species respond to germination triggering rains and other cues throughout a growing season. To do so, we simulated germination triggering rain events at 7 times during the growing season for 13 populations from 11 species of Streptanthus and Caulanthus (jewelflowers). We hypothesized that the rate of germination and amount of germination would vary among cohorts, expecting germination to be highest and fastest for earlier cohorts. We predicted lower germination percentages and rates among the Caulanthus study species, due to their desert origins. Due to the arid environment, these seeds may have an extended dormancy period in comparison to the Streptanthus seeds.
Results/Conclusions
Preliminary findings for this study indicate that the rate and percentage of germination differed among species and cohorts. As expected, generally germination was highest and fastest for earlier, but not necessarily the earliest, cohorts. Specifically, rates of germination were higher for all species in earlier cohorts, but there were substantial delays in germination and decreases in the amount of germination for all species as the season progressed. Streptanthus polygaloides, had high germination in each cohort, while germination of other species was more restricted to particular cohorts. This research provides insight on jewelflower niches and how they will be affected by dramatic changes in climate. As temperatures increase and weather patterns change, it is important that we understand how plants react to these changes and what they mean for population persistence.