PS 43-167 - Analysis and modeling of seed germination patterns across environmental gradients in four conifer species.

Abstract: Background/Question/Methods

Seed germination is a vital step in the plant life cycle, directly influencing seedling establishment and subsequently determining population persistence and species distribution. Germination is also highly sensitive to climatic conditions and may vary among species and populations due to local adaptation. Our study aimed to understand phenotypic plasticity in germination patterns and strategies to adapt to environmental gradients. We focused on four tree species (Pinus contorta, Picea engelmannii, Pinus ponderosa, and Pseudotsuga menziesii), collecting seeds at 5-6 sites per species for a total of 22 sites. Sites spanned the elevation range of each species in the Western U.S. The climate at the sites was characterized using Principal Component Analysis (PCA). For each site, seeds were divided into multiple lots, and each lot was exposed to a temperature ranging from 5 to 40°C with an interval of 5°C. Germination was tracked for 30 days. For each species, the median germination rate (GR₅₀) and maximum germination percentages (P_MAX) were derived from time-to-event models and fit to beta functions in thermal models to estimate five parameters (b (curve shape coefficient), d (maximum value of the variable), X_b (minimum temperature at which germination occurred), X_o (optimal temperature for germination), and X_c (maximum temperature at which germination occurred)) for P_MAX and for GR₅₀. Finally, we fit a linear model for each parameter of each response to determine whether they varied with species identity and the climate-derived PC scores.

Results/Conclusions

Our two-step modeling approach successfully delineated temperature response curves for each species. The climate at the collection sites varied with respect to chilling and growing degree days (PC1; 64% of variance), climate moisture deficit and precipitation (PC2; 19%), and relative humidity and beginning of frost-free period (PC3; 8%). P_MAX varied among species in d and X_c in PC1, X_o in PC2, and Xc in PC3 scores. GR₅₀ differed among species in b, d, and X_b in PC1, X_b, and X_o, and X_c in PC2 scores. In some species, some parameters in both P_MAX and GR₅₀ also showed variations within species. Preliminary results showed that seeds from different species and elevations could have different germination patterns that help explain their ecological niche. This variation may improve the chance of species persistence under climate change, mitigate species’ vulnerability to changing climate, and provide species’ capacity for adaptation. We anticipate applying these understandings to predict population dynamics and range shifts under climate warming.