Abstract: Soil moisture is one of the most important factors affecting plant growth. Investigating the responses of seedling growth and biomass allocation to drought stress on different soil substrates could provide theoretical support for the cultivation of high-quality afforestation seedlings. Here, 2-year-old Quercus mongolica seedlings were chosen as research object and an experiment was conducted under completely random design and with two factors (water levels and substrates). There were four water levels \[normal water supply (CK), mild water stress (T1), moderate water stress (T2), and severe water stress (T3), corresponding to 80%, 60%, 40%, and 20% of field water capacity respectively) in humus and clay. The height, ground diameter, crown area, leaf area, specific leaf area (SLA) and organ biomass of seedlings were measured in 20, 40, and 60 days. The results showed that the height and ground diameter of seedlings were decreased with increasing water stress intensity, and they had a significant difference betweenhumus and clay. The SLA of seedlings significantly differed among water stresses. The leaf areaindex and leaf biomass were higher in humus than in clay. After 60 days of water stress, with increased stress intensity, the total biomass and organ biomass  showed a descend trend in humus. The total, root and leaf biomass were 39.98, 22.32, 6.16 g per seedling and were the highest in T1 in clay. The results of redundancy analysis showed that soil total N, total P, available P, evaporation rate, permeation rate and aeration porosity had a significantly positive relation with seedling morphology, whereas soil bulk density, total porosity and water absorption capacity exhibited a negative relation with seedling morphology. The plasticity index of organs’ dry weight was higher than organs’ mass ratio on the whole. The soil substrates with an abundant nutrients and favorable soil structure could alleviate the negative effects of water deficiency on the growth of Q. mongolica seedlings. It’s necessary to rationally dispose soil and manage water for seedlings and thus improve the tolerance of seedlings to environment and their performance in afforestation.

Key words: Lyusi fishing ground, trophic level, stable carbon and nitrogen isotope, coastal water