Abstract: Soil water characteristic curve as a characterization of water holding capacity and the description of the function relationship between matric potential ψ and water content θ is the key to study the soil water infiltration, evaporation, soil erosion and solute transport. Affected by alpine climate characteristics, organic matter was extensively accumulated on the Tibetan Plateau. In order to determine the factors influencing soil water retention of active layer in permafrost regions, especially the influences of organic matter, samples was collected and analyzed from the Beiluhe Basin of the Tibetan Plateau. The results indicated that compare with soil particle-size distribution, bulk density and organic matter were the major factors that influenced the water holding capacity. High matric potential (0 to -30 kPa) was given priority to with bulk density while low matric potential (-100 to -1 500) kPa)was given priority to with organic matter; organic matter can affect soil water retention by altering soil structural and enhancing soil sorption, meanwhile, the influence extent depended on organic matter content with a positive correlation. This study were useful for understanding soil hydrological characteristics and provided theoretical basic for hydrological process in alpine region.

Key words: Tibetan Plateau, soil water characteristic curve, Pedo-Transfer Functions(PTFs), organic matter.