RESUMO
PREMISE: In temperate sand dunes, rising air temperature from climate change could not only further elevate surface soil temperatures during summers, but also drastically change the range of soil temperatures in other seasons. Winter warming may shift the timing of seed germination of dune species that require cold stratification for dormancy release. METHODS: We assessed the effects of temperature on dormancy and germination of Viola grayi seeds and evaluated whether winter warming could affect its germination phenology by conducting germination experiments and analyzing soil temperature data in cold and warm winters. RESULTS: Viola grayi seeds were dormant when dispersed in spring. One-month moist-chilling treatment (4°C) effectively released dormancy, while short, intermittent lower temperatures (alternating 20°/5°C) did not. Continuous higher temperatures induced secondary dormancy in nondormant seeds. During a cold, snowy winter, the surface soil temperatures of the sand dune remained at 0°-2°C for approximately 1 month owing to the accumulated snow, while the period of such stable low soil temperatures was much shorter during a warm, less-snowy winter, and the highest soil temperature reached 20°-25°C. These results suggest that dispersed seeds germinate in the following spring after winter chilling, but they may remain dormant after warm winters. CONCLUSIONS: With winter warming, seed dormancy of V. grayi seeds could be prolonged and the associated germination delayed. Assessing the minimum requirements for dormancy release and the potential to form persistent soil seed banks is important for judging the necessity and urgency of conservation efforts for temperate dune species.