Abstract: To clarify growth adaptation strategies of Pinus sylvestris var. mongolica seedlings under different soil water contents, two-year-old seedlings were grown under different water conditions, i.e., 80%, 60%, 40%, and 20% of soil field water capacity (SFC) for 15, 30, 45, and 60 days. We measured the contents of soluble sugar, starch, non-structural carbohydrate and biomass of different organs. The results showed that height, basal diameter, and  one-year-old needle, fine root and total biomass decreased with decreasing soil water content. Under soil water content of 80% SFC, soluble sugar concentrations were higher in stems and lower in current-year needles and fine roots, while starch concentrations were higher in stems and coarse roots. Under 60% and 40% SFC, soluble sugar concentrations were higher in needles and fine roots, while starch concentrations were higher in stems and one-year-old needles. Under 20% SFC, soluble sugar concentrations were higher in current-year needles and lower in one-year-old needles, while starch concentrations were higher in fine roots and lower in stems and coarse roots. These results indicated that P. sylvestris var. mongolica seedlings had higher growth rate and stress resistance under 80% SFC, exhibited higher resource utilization efficiency and optimal carbon storage strategy under 60% and 40% SFC, and stopped growing under 20% SFC. Therefore, soil water content should be maintained above 7% to promote natural regeneration of P. sylvestris var. mongolica plantation in Horqin Sandy Land.

Key words: seedling growth, carbon limitation, biomass allocation, moisture threshold, natural regeneration.