Altitudinal variations in germination and growth responses of Reynoutria japonica populations on Mt Fuji to a controlled thermal environment

The authors examined altitudinal variations in the thermal responses of seed germination and seedling growth in Reynoutria japonica (=Polygonum cuspidatum) under controlled environmental conditions. Seed populations were collected from different altitudes on Mt Fuji in Japan. The mean seed weight of the upland populations (above 1500 m) was significantly (1.5-fold) heavier than that of the lowland populations (below 1400 m). Under the lowest temperature regime of 15/10°C (day/night) the upland populations showed a significantly higher percentage and speed of germination than the lowland populations; this was not significant under higher temperature regimes. These results indicate that the germination traits of the upland populations on Mt Fuji are favorable for colonization in their cold habitats (low temperature and short growing season). Growth and shoot development were compared between the seedlings grown from seeds collected at altitudes of 700 and 2420 m. The upland seedlings showed a significantly larger biomass and leaf area than the lowland seedlings at 15°C, but there was no difference at 25°C. The difference in biomass at 15°C was attributed to the difference in seed weight. The upland seedlings produced a significantly larger number of branches with smaller and more numerous leaves at both 15°C and 25°C. these developmental traits of the upland seedlings were considered to represent the adaptation of the life form to upland environments. It was concluded that the R. japonica populations along an altitudinal gradient on Mt Fuji can be classified into two ecotypes, whose distribution border lies at an altitude of about 1400-1500m. In this study, the seed weight and germination traits of two R. japonica seed populations collected in Chiba Prefecture were briefly compared with those of the lowland populations on Mt Fuji.