How Warming Shapes Early Life Stages of Alpine Cushion Plants

Alpine tundra is a harsh environment with short growing seasons, low temperatures, and nutrient-poor soils. These ecosystems are warming faster than the global average. Yet how this rapid warming shapes the early life stages of alpine plants is not yet fully understood. Early life stages such as seed germination and seedling survival and growth are some of the most vulnerable life stages in a plant’s life, potentially posing a bottleneck to recruitment. In summer 2023, we collected seeds from three alpine plant species—Silene acaulis, Minuartia obtusiloba, and Phlox condensata—at the Niwot Ridge LTER, CO. Using a controlled germination study, we examined how germination success, seedling survival, and seedling biomass vary with temperature (4, 12, 20, and 28°C; the former two temperatures represent current conditions while the latter two represent projected conditions). Germination success increased with temperature across all species (p = 0.01), with germination peaking at 20°C. Although germination declined at 28°C, germination remained higher at 28°C than at 4°C and 12°C. Temperature significantly affected survival probability (p = 0.003), consistent across species. Survival remained near 100% up to 20°C, then sharply declined at 28°C. Biomass was marginally affected by temperature (p = 0.14), tending to increase up to 20°C before declining at 28°C. Results suggest a mismatch under projected warming wherein germination increases but survival decreases. This highlights the need to understand life-stage-specific thermal performance. Understanding variation in germination and early growth under different thermal conditions is essential for predicting plant population persistence, particularly in alpine ecosystems vulnerable to climate change.