Abstract: Four year old transplanted Pinus tabulaeformis seedlings were grown in pots under the treatment of three different levels of natural light intensity, soil moisture content and seedling water content. The root activity of transplanted P. tabulaeformis seedlings under the interaction of three factors was studied. The results showed that the root activity of transplanted P. tabulaeformis seedlings was reduced gradually with the decrease of natural light intensity and seedling water content and the increase of soil moisture content. The root activity of transplanted P. tabulaeformis  seedlings under natural light was significantly higher than that under shadow when seedling water content was 63% or soil moisture content was 30%; when the transplanted seedlings were under one of the conditions of natural light, 63% seedling water content or 30% soil moisture content, the root activity of transplanted seedlings was significantly changed with the change of other two factors; when the transplanted seedlings were under the natural light intensity and 53% natural light intensity, or 30% and 50% soil moisture content, the root activity was reduced with the seedling water loss.

Key words: Pinus tabulaeformis, light conditions, soil moisture, seedling water content, root activity, interaction