Abstract: [Objective] In order to provide a reliable theoretical basis and valuable technical ways for the maintenance, restoration, and improvement of soil functions, the paper revealed the reasons and mechanism of the degradation of the quantity and quality of soil organic matters of plantations in China and its influence on the growth of forest trees.[Method] On the basis of the research results in the field of forest soil organic matters in years, and with reference to the extensive literatures both home and abroad, the paper gave an in-depth discussion of the reasons and mechanism of the degradation of the quantity and quality of soil organic matters and its influence on forest trees.[Result] Soil organic matter is the core of forest soil fertility, not only as the organic nutrient pool, but also the inorganic nutrient pool. Leaf litter is the main source of soil organic matters, and its quality and quantity has a close relationship with the quality and quantity of the organic matters as well as the growth of trees. Repeated rotation of pure coniferous forest has brought about the deterioration of soil chemical properties and the degradation of soil biological activities with a special composition of the litter-fall and its acid decomposition. Repeated planting of pure forest leads to a decrease of the number and the contents of the important bio-chemical active substances in soil, further leads to degradation of soil functions. For repeated planting of pure coniferous forest, the composition and construction of its soil organic matters has obviously deteriorated and the number of important functional guilds has decreased.[Conclusion] The paper discussed the close relationship among the contents of soil organic matters, the physic-chemical characters, the biological activities and the growth of forest trees. It revealed the reasons and mechanism of the degradation of quantity and quality of soil organic matters by bad forest management technological measures and its influence on the growth of forest trees. To develop mixed forest to form a fine structure of community and improve the quality and quantity of soil organic matters is the future development trend for China's planted forest.

Key words: soil organic matter, quantity and quality of soil organic matters, coniferous plantation, broad-leaved plantation, mixed plantation, soil amino acids, soil polysaccharide, soil enzyme, soil microbial groups, infrared spectroscopy