Abstract: Soil moisture is a key environmental factor affecting seed germination and seedling growth. To investigate the effects of soil moisture on seedling emergence and growth of Leymus chinensis andMedicago sativa under natural conditions, a simulation study was conducted with six soil moisture levels (2.5%, 5%, 7.5%, 10%, 20% and 30%). The results showed that the seedling emergence rate and seedling growth of both species were significantly affected by soil moisture. With increasing soil moisture, the seedling emergence rate was first increased and then decreased. ForM. sativa, the seedling emergence rate was the highest (up to 93%) when the soil moisture was 10%-20%; the lowest seedling emergence rate was 2% at 30% soil moisture level. For L. chinensis, the highest seedling emergence rate was 76% when the soil moisture was 5%; the lowest rate was 9% at 30% soil moisture. With the increases of soil moisture, root length and seedling height first increased but then decreased, which was consistent with the pattern of seedling emergence rate. The optimal soil moisture level was 7.5%-10% for seedling emergence and growth of M. sativa, and 5%-7.5% for that ofL. chinensis seeds. In conclusion, soil moisture at 7.5%-10% would be suitable to the sowing and seedling growth of M. sativa, and 5%-7.5% for L. chinensis.

Key words: biomass allocation, Fraxinus mandshurica., Pinus koraiensis, nitrogen addition, water stress