Abstract:

Based on the detailed investigation of fine root vertical distribution characteristics in man-made Robinia pseudoacacia forest in Ansai County, Shaanxi Province, a model of Robinia pseudoacacia's fine root vertical distribution, S=Ah^B(C+Dh+Eh²+Fh³3), was established, which reflected growth of the fine root surface areas that influenced by the hybrid process of infiltrating water and deep level water. In this formula, A、B、C、D、E、F were experience coefficients, especially A>0、B>0、F≠0, S was the fine root surface areas values in a certain depth of soil(cm²·dm^-3 ), h was depth of soil(cm). The maximal depth of fine root distribution h_max and the depth of fine root's maximal distribution values h_p in theory can be determined, and also can got the fine root growth's maximal depth h_q which influenced by infiltrating water, h_q approximately was considered as the boundary point of infiltrating water and deep-site water to influence fine root growth. According to the model of Robinia pseudoacacia's fine root vertical distribution, the soil water in Robinia pseudoacacia woodland in vertical section could be divided into three layers: the first layer was water exchange activity layer, which was from soil surface to h_p, which was greatest influenced by precipitation. The second was soil water attenuation layer, which was between h_p and h_q, influenced by precipitation, water and fine root vertical distribution had the same change trend in the layer, they were all slow decreases from h_p to h_q. The third was soil water relatively stable layer, which was under h_q, hereunder soil water became relatively stable. The model could explaine the relationship between fine root distribution and soil water in a certain extent, and prove the causes of soil drification in the Loess Plateau, and provide theoretic basis for further carrying out the policy of matching tree species with the sites in the Losses Plateau.

Key words: Robinia pseudoacacia, fine root, model, sites