COS 208-5 - Among‐population variation in seed germination behaviors may improve the chance of two common conifer species persistence under climate change in the Pacific Northwest, USA.

Background/Question/Methods

Seed germination is vital in plants’ life cycle and influences seedling establishment and survival, subsequently determining population persistence and species distribution. Seed germination is highly sensitive to changing climate and may vary among populations due to local adaptation. However, among-population variation of seed germination to environmental change was rarely studied. Our study aims to test whether seeds from different elevations have different germination behaviors in various temperatures and understand species’ phenotypic plasticity and strategies to adapt to environmental gradients. We anticipate applying these understandings to predict population dynamics and range shifts under climate warming. We used seeds of two common conifer species from different elevations to run the seed germination test at temperatures from 5 to 40°C with an interval of 5°C. Numbers of germinated seeds were observed every day and removed from dishes for 30 days. We applied a two-step thermal time-to-event model to seed germination data. The log-logistic function was used in the time-to-event model, and the Likelihood Ratio Test (LRT) was used to check the differences among time-to-event models. Germination rates at the 50th percentile of seeds germinated (GR50) and maximum germination percentages (PMAX) were derived from time-to-event models and fit to beta function in thermal models.

Results/Conclusions

The LRT results showed that germination behaviors are different among elevations within species in the same temperature, except in the extremely high (40°C) and low temperature (5°C). Both seeds of Engelmann spruce and lodgepole pine did not show specific trends of GR50 and PMAX along the elevation gradients, nor did seeds from the central population have higher GR50 and PMAX. The variabilities of GR50 and PMAX among elevations in different temperatures for each species have disparate patterns. The variabilities were the smallest at the optimal temperature (20 to 25°C) and became larger when temperatures deviated from the optimum toward the suboptimum (10, 15, 30, 35°C). Our study showed that environmental gradients are unreliable predictors of variation among populations, and responses are often individualistic. As the pattern of this variation is inconsistently reflected among populations within species, we cannot make simple generalizations about how this variation is allocated across geographic ranges or gradients. However, we found that variations are larger at suboptimal temperatures, which plants will be exposed to in the future climate. Therefore, we deduce that variations at suboptimum improve the chance of species persistence under climate change, mitigate species’ vulnerability to changing climate, and provide species’ capacity for adaptation.