| This paper choose the eucalyptus plantation which was planted after returning farmland to forest in Xing Bin district of Lai Bin city in Guangxi as the research object, adopting diameter class standard wood as the method of studding biomass of eucalyptus plantation tree layer, and estimated its productivity, and analyzed the carbon and nitrogen, phosphorus and potassium nutrient elements content, reserves and its distribution of the ecosystem, finally discussing the characteristics of stoichiometry and the correlation of carbon and the nutrient elements of tree layer, soil layer and litter layer, with the purpose of understanding the ecological benefits of eucalyptus as a tree species of returning farmland to forest in the mature forest stage.The results show that:(1) After returning farmland to forest, total biomass of 8 years old eucalyptus plantation ecosystem was 134.30 t/hm2, the order of biomass for each layer was:tree layer> litter layer> shrub layer> herb layer, the biomass of tree layer accounted for 88.99% of the system total biomass, the distribution biomass of each organ was : stem> root tip> bark> branch> coarse root> leaf> middle root> fine root.(2) The net productivity of 8 years old of eucalyptus plantation was 19.36 t·hm-2·a-1, and the net productivity of tree layer 16.44 t·hm-2·a-1, the productivity of the stem was 9.77 t·hm-2·a-1, accounting for 59.46% of the total productivity tree layer.(3) The carbon content in various organs of the tree layer ranged from 386.42-505.37 g/kg, and the average carbon content was 468.18 g/kg, with an order of leaf> stem> root tip> middle root> coarse root> branch> fine root >bark. The carbon content of shrub layer and herb layer, litter layer were 451.54,436.76,450.28 g/kg; and the carbon content in 0-20,20-40 cm of woodland soil layer were 9.24,10.70 g/kg.(4)The total carbon reserve of eucalyptus plantation ecosystem was 113.86 t/hm2, with the distribution pattern of tree layer>soil layer>understory layer (litter layer> shrub layer>herb layer). And the net amount carbon of tree layer was 7.70t·hm-2·a-1.(5) Soil organic matter, total nitrogen, total phosphorus and available nutrients of N, P, K content in eucalyptus plantation decreased, but total potassium content increased, and found the soil rich of N nutrient but lack of phosphate fertilizer.(6) The total reserves of N、P、K nutrient element of eucalyptus plantation ecosystem was 181.56 t/hm2, including soil layer (0-40 cm) accounted for 99.61%, only 0.39% of vegetation. Eucalyptus plantation producing 1 t dry matter of biomass required a total of number of N, P, K for 4.55 kg, and utilization efficiency of three kinds of nutrient elements were as follows:P>K >N.(7) N and P, K, P and K were significantly positive correlation in tree layer; The correlation between Leaf, fine root, bark and stem were different. Only P and K was significant positive correlation in soil layer. The carbon and nutrient element in soil had different influences on leaves and fine root of tree layer, the correlation between soil nutrient and litter were not significant, And there were significantly statistical difference in C： P, C：K, C：N, N：P of tree layer, litter layer and soil layer. |
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