The Variability and Determinants of Serotiny in <i>Pinus Yunnanensis</i>

Serotiny, a key fire-adaptive trait, enables certain plants to retain seeds in closed cones until triggered by fire, thus facilitating post-fire regeneration. Although serotiny has been observed in many species, the physiological and environmental mechanisms that regulate this trait remain poorly understood. In this study, we investigated the variation in serotiny level within <i>Pinus yunnanensis</i>, a pine species native to fire-prone landscapes in southwestern China. Serotiny level varied significantly among populations and was significantly associated with environmental factors and cone physiological characteristics, including Bio2 (mean diurnal temperature range), Bio5 (maximum temperature of the warmest month), soil pH, total soil phosphorus, and cone resin content. Cone resin content exhibited the strongest direct positive effect on serotiny. Soil pH and phosphorus concentration negatively affected resin content in cones, thus indirectly reducing serotiny level. Bio2 enhanced serotiny indirectly by acidifying soil and promoting resin synthesis, while Bio5 decreased serotiny indirectly by increasing phosphorus availability and limiting resin accumulation. Recent fire activity and fire radiative power did not appear to have a significant effect on serotiny in <i>P. yunnanensis</i>. These findings enhance our understanding of how serotiny evolves under the combined pressures of climate and soil conditions in fire-adapted ecosystems.