University of California, San Diego La Jolla, California, United States
Background/Question/Methods
California poppy (Eschscholzia californica) is an abundant, widely distributed species often used in restoration. Recent research has shown that southern populations are better adapted to drought than northern populations, suggesting that restoration success might benefit from sourcing seeds from southern populations. However, it's unknown whether these populations vary in their germination cues. Here, we asked whether germination cues for E.californica vary with temperature and daylength, using seeds from nine populations collected across California. We treated all seeds either with gibberellic acid (GA) or deionized water (GA breaks dormancy, which is common in the southern populations), to determine if gibberellic acid alters germination. Seeds were grown in a growth chamber under factorial combinations of daylength (short = 10 hours, long = 14 hours) and temperature (warm = 24.4 degrees C day, 17.2 degrees C night; cool = 18.3 degrees C day, 10 degrees C night), and germination was checked daily for three weeks, which captures the majority of germinating seeds.
Results/Conclusions
Although GA treatment increased the number of germinating seeds compared to DI water, GA treatment did not impact the days to germination. Short daylength and warm temperatures accelerated germination for E. californica. The least germination was observed in the long daylength cool treatment; note that this combination would be unlikely, since the winter growing season for this species coincides with short days and cool temperatures. There was clinal variation in time to germination, where seeds from more arid, southern collection sites germinated more slowly than seeds collected from more mesic, northern sites, and there were also statistical interactions between site aridity and temperature and daylength manipulations. These findings suggest that rising temperatures are unlikely to reduce germination rates of E. californica during restoration, but that sourcing seeds from other populations at different latitudes could cause a change in germination timing due to interactions with novel daylengths.
