Effects of sowing dates and burial depth on seedling emergence and survival of Calystegia soldanella Roem. et Schult. and Lathyrus japonicus Willd

We aimed to accumulate the useful information of Calystegia soldanella and Lathyrus japonicus for the conservation of them and as the landscape material in coastal sand dune. The germination ecology of them was investigated. Seeds of both species, which collected in the Hokkaido Ishikari beach, were treated with sulfuric acid to release the hard seed dormancy. Seeds were sown in sand dune with various burial depths in the autumn and next summer. In the sowing in autumn, seedling of C. soldanella emerged at the highest 89% from the burial depth 5 cm, and the emergence rate was decreased with the burial depth and even at 1 cm of depth. In the sowing in summer, highest emergence rate was shown from the burial depth 5 cm as well as the sowing in autumn, though emergence rates decreased less than sowing in autumn at the each burial depth. In the sowing in autumn, L. japonicus showed good emergence rate of 60-76% from 1 cm to 15 cm of burial depth, and it was the lowest at burial depth 1 cm. The highest emergence rate in the sowing in summer was 11%. The dry sand layer, which became extreme high temperature and dry, was considered as the cause of decreasing in emergence rates of both species in summer or at the burial depth of 1 cm. The influence of the burial depth of 5 cm or more on the emergence was different in both species. It seemed that this reason was a difference of the soil penetration power of both seedling.