Fine Root And Grass Root Growth And Turnover In A Complex Ecosystem Of Triploid Populus Tomentosa- Lolium Multiflorum Lam

This research had been carried out in a complex ecosystem of Triploid populus tomentosa — Lolium multiflorum Lam at Tianquan County. The poplar trees had been planted in May 2000. By using sequential soil core method to observe the following aspects:(1) the standing biomass of fine root and grass root, the seasonal dynamics of their nutrient and chemical composition; (2) net productivity, turnover and decomposition of fine root and grass root;(3) the spatial distribution of fine root etc. From this study we get these results as follows:The standing biomass of fine root and grass root was 0.611 t·hm^-2and 0.132 t·hm^-2 respectively. Fine root(0¹mm)pools(57.9%)was a principal part in tree stratum and undergrowth occupied 15.7% of total amounts of fine roots. The standing biomass of live and dead fine root(0¹mm)showed a double-apices curve being highest separately in September and May or in March and July, and being lowest separately in January and August or in December and May. In contrast, the seasonal dynamics of live fine root(1 2mm) showed a single-apex curve, and the maximum and minimum were in July and January respectively. But that of dead fine root(1²mm) showed a irregular fluctuation with the season. The seasonal dynamics of grass root have a same trend with fine root(0 1mm).There were a little different between fine root and grass root in the horizontal distribution, but be a reverse result in the vertical distribution. The vertical distributions of the fine root(0¹mm)and live fine root(1²mm) is: upper layer>middle layer>down layer, and the biomass of upper and middle layer occupied about 50% and 30% corresponding. That of the dead fine root(1²mm)is: middle layer>down layer>upper layer, and the biomass of middle and down layer occupied about 45% and 40% corresponding. The vertical distribution of grass root showed an "T" curve, the biomass ofsoil layer of 0 10cm account for 85%.The maximum and minimum chemical composition content of fine root was ligninand coarse albumen. The content of lignin of fine root(0^lmm)was lower than fine root(l²mm), but the content of cellulose was opposition. The chemical composition content of grass root is: hemicelluloses>ash and lignin>benzene-alcohol extraction and coarse albumen. The ash content of grass root was higher than fine root.Nutrient concentrations of the nitrogen and magnesium of fine roots were negatively related to root diameter size. The maximum nutrient concentration of fine root and grass root were kalium and phosphorus. There exist different seasonal fluctuation of nutrient concentrations in fine roots and grass root for the different elements.Rate of weight loss of fine root and grass root showed exponential relationship with time, with yearly weight loss of 16.11%, 69.80°/^ 73.44% and 79.53% for fine root 00— lmnK 01²mnK 0O²mm and grass root respectively. Generally, the course of nutrient dynamics during the decompositions follows as: (1) The content of N and Ca increased in the course of fine root decomposition. Adverse by the content of P>K and Mg declined;(2) The nutrient content of grass root were irregular during the decompositions; (3) The remaining percentages of P> K and Mg had a same trend as weight loss during the decomposition of fine root, but the remaining percentages of N and Ca had a slight decrease; (4) The remaining percentages of nutrient had a same trend during the decomposition of grass root.The net productivity^ mortality and decomposition of fine root in stands totaled to 0.3337n 0.3203 and 0.3040 t-hm'V respectively. And all of them were: 0^lmm>l 2mm. These indicated fine root(0^lmm)was the principal part of turnover of the community. Annual turnover rate of fine root 0^lmm and l²mm were 0.65 and 0.74 respectively.In conclusion, in certain range above sea layer of west edges of Sichuan basin, it was a comparatively suitable popularization mode.