[Hydrological functions of the litters and soil of tropical montane rain forest in Xishuangbanna, Yunnan, China].

A study of the hydrological functions of litters and soil of the tropical montane rain forest in Xishuangbanna was carried out. The results showed that the soil bulk density decreased with the increase of altitude, while the soil total porosity, the noncapillary porosity, the capillary porosity, the maximum soil moisture rate, the maximum water holding capacity, the effective water holding capacity, the soil moisture increased with the increase of altitude with local fluctuation. In addition, the soil moisture in early stage of rainy season, the saturated water content and the effective reservoir space increased with the increasing altitude, and the saturated water content and the effective reservoir space had a significant difference at different altitudes (P<0.05). The soil permeability had a significantly positive correlation to the soil total porosity and non-capillary porosity (P<0.01), moreover, the soil non-capillary porosity had a more significant effect on the soil permeability. The thickness of under-composed layer at different altitudes was half more than that of the total litter thickness, which showed that the under-composed layer > semi-decomposed layer. The total volume of litters and the ratio of the volume of semi-decomposed layer to the total volume of litters increased with the increasing altitude, which indicated that the decomposition speed of litters was slower at a low altitude and faster at a high altitude. The maximum capacity of soil moisture, the maximum rate of soil moisture, the natural moisture rate, the effective rate of interception and the effective capacity of interception increased with the increasing altitude in under-composed layer and semi-decomposed layer, and their values in under-composed layer were higher than those in semi-decomposed layer. However, the depth of effective capacity of interception decreased with the increasing altitude with local fluctuation. Comprehensive analysis demonstrated that the water conservation ability was stronger at a high altitude and weaker at a low altitude. The water holding capacity of litters at different altitudes increased and the water absorption rate of litter decreased with the soaking time, while after 12 hours, the water absorption rate of litters gradually became saturated. Moreover, the water holding capacity of litters at different altitudes and soaking time had a logarithmic relationship, and the relationship between the water absorption rate of litters and soaking time was described by power function. In short, there was a stronger water conservation function at high altitude compared with low altitude of the tropical montane rain forest in Xishuangbanna.