Silene acaulis early-life responses to experimental warming vary with parent-population microclimate

Abstract

Arctic ecosystems are warming at disproportionate rates, placing pressure on slow-reproducing perennial species with limited capacity for rapid evolutionary adaptation. This study examined how simulated warming affects germination probability, germination timing, early survival, and seedling growth in Silene acaulis, and whether population-level variation in these responses reflects microclimate-specific local adaptation. Seeds from ten populations spanning a snowmelt gradient at Latnjajaure, within the Swedish low-Arctic, were grown under control conditions based on median Latnjajaure July temperature, and a heated treatment set at +4°C above the control. Warming was broadly beneficial across all measured outcomes. Germination odds approximately tripled under heating, germination timing advanced by approximately one week, seedlings were consistently larger at all ages, and final survival rates were approximately thirteen percentage points higher under warming. However, growth rates plateaued under heated conditions, accompanied by visible desiccation in larger seedlings, suggesting that heat stress may impose constraints over longer timescales. Population-level variation in warming response was detected, most strongly for germination probability, where a significant treatment × snowmelt interaction indicated that seeds from warmer, early-snowmelt plots showed a greater relative increase in germination probability under warming than those from colder, late-snowmelt plots. Altitude independently influenced germination timing, with seeds from higher-elevation plots germinating consistently later regardless of treatment. Variance partitioning revealed that population origin explained a substantial proportion of variation in seedling size. The observed phenological differences between populations at Latnjajaure are consistent with population level variation. Although these cannot truly be distinguished from maternal effects, the evidence and literature point to at least a partial genetic component, potentially including microclimate specific adaptation. These results highlight the importance of considering intraspecific variation when predicting how Arctic species will respond to climate change, particularly for foundation species such as S. acaulis whose population health has cascading consequences for the broader communities they support.