Abstract: The relationship between soil moisture diffusivity (D(θ)) and soil moisture (θ) at 0-100 cm soil profile was measured by the horizontal infiltration method in three habitats in Horqin Sand Land, i.e., sandy grassland, fixed sand dune, and mobile sand dune. Also, the relationship between D(θ) and Boltzmann parameter (λ) and θ, and the changes of D(θ) across the soil profile for each habitat were considered in this study. The results showed that (1) there was a significant difference in the moving rate of soil wetting front among the three habitats, and the average rate values were 0.38, 0.97 and 1.6 cm·min^-1, for the sandy grassland, fixed sand dune, and mobile sand dune, respectively. The moving rate for the three habitats all decreased with increasing in infiltration distance in a logarithmic function. (2) The λ values for the soil profile (0-100 cm) were 4.22, 6.58 and 8.59 cm·min^-1/2 in the sandy grassland, fixed sand dune and mobile sand dune, respectively, and decreased gradually with the increase of soil moisture. (3) The lowest, intermediate and highest soil moisture diffusivities for the 0-100 cm soil layer were found in the sandy grassland (1.21 cm²·min^-1), fixed sand dune and (4.51 cm²·min^-1) and mobile sand dune (12.75 cm²·min^-1), respectively. The relationship between soil moisture diffusivity and soil moisture for the three habitats was fitted much better by an empirical equation, D(θ)=ae^bθ. There was no consistent trend of D(θ) with increasing in soil depth for all the three habitats. This implied that there was a large difference in D(θ) among different habitats and between different soil depths for the same habitat, and D(θ) had higher spatial heterogeneity in this region. (4) Soil organic matter content and the clay+silt content (<0.05 mm) were the key soil factors negatively affecting D(θ). In addition, habitat type and plant root depth also had some influence on D(θ).

Key words: heterotrophic nutrition, molecular nutrition markers., symbiotic coral