| Based on the climate conditions and current introduction situation of Eucalyptus grandis in Hunan province, an effective measure was taken to identify the cold resistant of E. grandis. At the same time, the amount of microbes, enzyme activity and their distribution in soil were measured. The relationship of the amount of microbes, enzyme activity and the content of nutrient elements in soil was also studied. Having studied the productivity, nutrients concentration and its biocycling of E. grandis plantations with different densities, the economic benefit of E. was evaluated and an optimal cultivation model was put forward for short-rotation industrial timber forest. Molecule identification technique of RAPD was employed to study genetic diversity of 11 E. grandis provenances. The main results of the research paper are as follows:1. An effective identification measure of cold-resistant of E. grandis was figured out and 2 elite provenances and 21 families were selected. Analysis for the composition and concentration of fatty acid in the leaves and stem of E. grandis was conducted by using gas chromatography. The fatty acid compositions were 16:0, 16:1, 18:1, 18:2 and 18:3 respectively. As a physiological indicator to evaluate the ability of cold-resistant, Index of unsaturation fatty acid (IUFA) could reflect the relative cold-resistant ability of E. grandis and has practical values. The result was proved to be correct by the test of living through the winter that the higher of IUFA in the cell, the stronger cold-resistant the plants have. The elite provenances are 18592 and 8594, and the elite families are No. 36, 37, 5, 6, 7, 11, 25, 40, 42, 43, 45, 53, 54, 66, 4, 6, 16, 33, 52, 56 and 78. After 32 months, the increment of average diameter at breast height was up to 8.5 cm, tree height reached 8.5 m and IUFA was over 170. The growth characteristic and IUFA had significant variance among different provenances and families. IUFA had a significant relationship with latitude and less relationship with other factors.2. The biomass and productivity of E. grandis plantation were studied and the law of density effect on stands biomass was found out. The biomass of individual tree decreased distinctly with the increase of the density, and that of the lower density stands was 1.48 times as much as that of higher density stand. While the biomass of the stand increased with the increase of the density, and biomass of the stand with high densities were 16.82 t ?hm~2 higher that of with low density. The annual net biomass reached 22.57, 24.85, and 25.37 t ?hm2 ?a"1 respectively, which was higher than that of Chinese fir plantation in central production areas. The component biomass of the stand increased with the increase of density, which exhibited the patterns of Wstem>Wroot>Wbranch>Wbark>Wleaf>W,ruit. The stand with middle density was observed as a reasonable stand structure in which the index of the leaf area was the highest and the stem biomass ratio reached more than 63%. The analysis of the economic benefit indicate that the stands with middle and low density have higher cost-profit percentage, ratio of output and input, internal rate of return, and short return term of payment, so the risk ofthis kind stand is lower. The result of sensitivity analysis showed that the price of products, production cost and total investment are the main factors which had great influence on the cost-profit percentage. After comparison of different factors, the suitable planting density of E. grandis is 900 to 1125 stems per hectare when E. grandis was planted to produce prowood and pulpwood, and a well economic benefit could be achieved.3. The biocycling rule of E. grandis was found out. The nutrients concentration varied in different components, highest in leaves and lowest in stem; the contents of K and N were the highest, and those of P was the lowest in macro-elements, and Mn and Fe highest and Cu lowest in microelements. Nutrient accumulation of individual tree decreased distinctly with the increase of the standing...
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