Research On Fine Root Characteristics In Alnus Formosana Forest Under Cultivated Forage Grass

Qualified pasture distribution dominated by plantation is a widely-used model in converting cultivated land into forests with the simultaneous combination of ecological and economic benefits. The paper makes a comparative reseach of Hemarthria compressa (L.F.)R.Br., Lolium multiflorum Lam. and natural grass marked "A+H", "A+L" and "A+N",by taking a sample with fan-shaped digging method in 8-year-old Alnus formosana artificial forests under different grass layers, carries an analysis of distribution characters in different models, vertical distribution, nutrients internal cycling, biomass, production and turnover rate of fine roots and the storage and distribution of soil organic carbon, and finally has a contrast of the fine roots characters of the two Alnus formosana artificial forests after being fertilized and changes of the soil organic carbon.Then we have come to the conclusions:1. The tillering ability of fine roots in unfertilized forest is A+N>A+H>A+L. There is a significant difference of tillering ability in the first order fine roots between fertilized and unfertilized forests, not significant difference in the third order of fine roots and significant difference in A+L and A+L+F, A+H forest only in the second order fine roots. The rules of fine roots eigenvalue dynamics are similar:the value decreased with soil deepening, the percentages of root length and area are more than biomass in the top soil layer. The relation-ship between fine root eigenvalue and soil depth can fit very well by y=ae-b2. The mean monthly biomass order of fine roots is:A+N> A+H> A+L+F> A+L> A+H+F, the live fine roots have two peak value in July and September during a year, the lowest value appears in December or next January; the order of fine roots annual production is:A+L+F> A+H> A+H+F> A+N> A+L, annual turnover rate is:A+H(1.384)> A+L+F(1.369)> A+H+F(1.341)> A+N(1.068)> A+L(1.038 times.a-1).3. The biomass retention rate of leaves is quicker than fine roots in the first 60 days, and then the rate is contrary because lignins of fine roots are more than leaves and biochemical process is dominant after 60 days. The retention rate of leaves is lower than fine roots after 1 year. Fine root have different release speeds in different inviroment, the order of decoposition constant K is:leaves(1.7547a-1)> fine root in A+L forest(1.039a-1)>fine root in A+H forest (0.9332a-1)>ine root in A+N forest (0.9178 a-1) The biomass and elements retention rate of fine roots and leaves biomass can fit very well by y=ae*bx. The nutrient return order is: A+L+F(13.797)>A+H+F(10.063)>A+H (9.250)>A+L(7.863)>A+N(3.632 kg.hm-2), it demonstrates that tree+pasture models can improve soil conditions.4. The N and K of Alnus formosana fine roots transport obviously in the course of senescence while not obvious about Ca and P. Ca can be looked on as a standard to evaluate other elements because it is steady in the course of senescence. The orders of nutrient transportation are not similar, the first is the 1st fine root, then 2nd fine root......it implies that the senescence orders are contrary to the growth order. The transport ratio decreases with the increase of soil nutrient; it proves that nutrient internal cycling is a strategy for plants to adapt to oligotrophic conditions. The nutrient transport response of fine roots is more obvious than leaves after fertilization.5. The mean nutrient content of fine roots is Ca>N>K>P, the peak value of N appears in Summer and the lowest value appeas in Autumn and Winter, while the peak of K appears in Winter and Spring, the content of P is contrary to K. Ca's content of fine roots in five models has no obvious rules.The order of C/N is A+N>A+L+F>A+L>A+H>A+H+F; There is a strong correlation between soil available N, K and the N, K of fine roots. There is a significant correlation between 0-20cm soil available N content and N of A+L+F fine roots. There is a strong correlation between soil available K and K of A+H fine roots, while it is not correlation of P and Ca between soil and fine roots.6. The soil organic carbon of tree+pasture model is more than natural grass model.The rules of organic carbon distribution are similar: it decreases with soil depth increasing; The dynamics of soil organic carbon is:it accumulates from Winter and the peak value appears in Summer, then it decreases and the lowest value appears in Autumn. It increases biomass, litter and soil organic carbon reserves after fertilized.