Response to photoperiods is one of primary physiological features in plants. In Arabidopsis thaliana, long-day photoperiod and vernalisation promotes flowering. Our target species A. kamchatica, closely related to the plant model, is distributed at 30—3000 m altitude in and around Japanese Alps that have heavy snowfall. Due to longer snow season and shorter growing season at high altitude, the species flowers in April—June at low altitude but in July—September at high altitude. To test within-species variation in photoperiod response for flowering time, we conducted growth chamber experiment with two photoperiods (16h, 8h) with or without vernalisation for 40 populations from various altitude.

Without vernalisation, five populations from relatively high altiude had higher proportion of flowering plants under short-day than long-day, possibly enabling their flowering after the summer solstice. With vernalisation, whilst high-altitude population more required long-day, low-altitude population well flowered under both long- and short-day, probably enabling their flowering soon after winter. These results indicate within-species variation in photoperiod response for flowering.