Effects of soil water regimes on the growth of Quercus mongolica seedlings in Changbai Mountains

This paper studied the response of the seedlings of Quercus mongolica, one of the dominant tree species in Changbai Mountains, to the artificially controlled three soil water gradients, including their morphology, biomass and photosynthetic characteristics. The results indicated that various water regimes significantly affected the biomass and its distribution pattern in the leaves, branches and roots, as well as the leal gas exchange. Under soil water stress, the crown structure changed, and the tree height, groundline diameter, single leaf area, and above-ground and belowground biomass were inhibited. As soil water content decreased, the ratio of belowground and above-ground biomass dry weight significantly increased. Water stress had a negative effect on net photosynthetic rate, CO₂ use efficiency and carbon use efficiency. The responses of stomatal conductance, transpiration rate and water use efficiency to water stress were complicated. Only at low soil water content, the stomatal conductance and transpiration rate significantly decreased, while water use efficiency increased. It was demonstrated that Quercus mongolica was the tree species with variable resistance to drought, and the resistance could be improved by long-term soil water stress.