A model for vertical distribution of fine roots in Robinia pseudoacacia plantations on the Loess Plateau

Abstract

Based on a detailed investigation of vertical distributions of fine roots in Robinia pseudoacacia plantations at the Ansai Soil and Water Conservation Station, Shaanxi Province, a model was developed for the deep distribution of fine roots of R. pseudoacacia, which reflects the growth of fine roots affected by the mixed process of infiltration water and deep soil water. The maximum depth of the distribution h_max and the depth of the highest fine root density (FRD) h_p were determined and the maximum depth of infiltration water supplied for fine root growth h_q could also be calculated, h_q was considered as the approximate boundary between infiltration water and deep soil water in support of the growth of fine roots. According to the model, the soil water of R. pseudoacacia woodland in the profile could be classified into three layers: the first layer from the soil surface to h_p was the active water exchange layer, very much affected by precipitation; the second was the soil water attenuation layer, between h_p and h_q and largely affected by the vertical distribution of fine roots;.the third was the relatively stable soil water layer below h_q, below which soil water did not change much. The percentage of infiltration water supplied for the growth of fine roots reached a level of 88.32% on the shaded slopes and 85.21% on sunny slopes. This indicated infiltration of precipitation played a crucial role in the growth of R. pseudoacacia in the gully region of the Loess Plateau. The research of interaction between the distribution of fine roots and soil water in the profile will help to explain the reasons for the complete drying out of soils and provide a theoretical basis for continuing the policy of matching tree species with sites on the Loess Plateau.