Research On Fine Root Growth Of Robinia Pseudoacacia And Its Relationship With Soil Moisture In The Loess Plateau

It is very important to establish the mathematical model of fine root growth, study the distribution of artificial vegetation roots and its relationship with soil moisture in quantitative method, and research the influence of deep soil moisture by artificial vegetation roots, for revealing the cause of soil desiccation layer in the Loess Plateau woodland, guiding the species choice of artificial tree or grass scientifically, speeding up the construction of Northwest Landscape Beautification Project.The paper established a model for fine root growth of Robinia pseudoacacia and a coupled model for the relationship between fine root growth and soil moisture, based on the data of artificial R.pseudoacacia fine root and soil moisture, investigated in Ansai county of Shaanxi province(semi-arid region) and Jingchuan county of Gansu province(sub-humid region). The main conclusions are as follows:1. The paper tested and verified that the model S = h^B( M + Nh + Uh² + Vh³)can good fit the fine root vertical distribution for R.pseudoacacia (where, S is fine root surface area density/cm²Â·dm^-3; h is soil depth/cm; B shows the soil depth where the values of fine root are the most; M,N,U,V are empirical coefficients), and calculated the maximum depth of fine root and the contribution rate of soil moisture to fine root growth. Based on the above, it established a compartment model S₂(h) = b(e^-k₂h- e^k₁h) for fine root surface area density, with the change of soil depth, verified its equivalence with the vertical growth model using numerical method, and offered the theoretical basis for the vertical growth model.2. The paper established a dynamic model S (t , h ) = e^-βt·h^B(e^α₁- e^α₂ h + e^α₃h² - e^α₄h³)for fine root growth (where,βis the attenuation rate of fine root surface area density with time;α₁ ,α₂,α₃,α₄ are empirical coefficients). The dynamic model could show the changes of fine root growth with soil depth and time, and can predict the state of fine root growth for R.pseudoacacia in different soil depth and time, in the Loess Plateau.3. The paper established a coupled model , 02·dm^-3) and soil moisture (W/%), with the change of soil depth (h/cm) and time (t/month). It is proved that the model could reflect the coupling relationship exactly. It displays the annual cyclical changes about fine root growth and soil moisture; the value of parameter a falls in between 0 and 1, which shows the root growth of R.pseudoacacia just absorbs part of the soil moisture and could not cause soil desiccation in the investigative area; parameter m indicates the hysteresis effect of soil moisture and root growth, which is between 10 to 20 day; parameters p, b and m reflect the difference of region where R.pseudoacacia grow, and parameter a reflects the biological characteristics of R.pseudoacacia - water demand of root growth.