| In this paper, physical and chemical characteristics of the Hippophae rhamnoides and Morus alba mixed plantation were analysed. The biomass and root distribution of mixed plantation on iron tailing were also systematically investigated. Moreover, the accumulation and distribution of heavy metal within this ecosystem are one of our focuses. The results were shown as follows:(1) Plant species in the mixed forest were not so rich. Layers in this communities were not obvious and there were only shrub layer and herb layer.The order of biomass per unit area was as follows: tree layer>litter layer>herb layer. 79.08 percent of total biomass was found in the forest layer, 12.15 percent was found in the shrub layer,and 3.77 percent was found in the herb layer. The order of biomass in different organics as follows: root>branch>stem>leave.(2) In biomass of root system of individual plant, the average biomass of root system of Hippophae rhamnoides was larger than that of Morus alba in layer of 0～80cm. Yet the average biomass of root system of Morus alba was larger than that of Hippophae rhamnoides in layer of 80～100 cm. In density of fine roots, Hippophae rhamnoide 's fine roots(<1mm) concentrated in the layer of 0～60cm, and sharply decreases below this layer. On the contrary, the highest density of fine roots(<1mm) of Morus alba was the layer of 0～20cm, and the change of fine roots'density was relatively even in the layer of 20～80cm ,but the density of fine roots sharply decreases below the layer of 0～80cm. It is concluded that both competition and cooperation exist between the two species.(3)Mean soil bulk density under mixed plantation in the layer of 0～40 cm was lower than that of soil on the new iron tailing. The total prosity and the ventage degree of soil in mixed plantation were all larger than that of the soil on new iron tailing, all of these seems to indicate that mixed plantation improve the physical properties in a great extent. Organic content of the soil on the iron tailing was relatively small(about 5.78～5.81 g/kg), while that of the soil under the mixed plantation was increased dramatically. The order of content of chemical elements were as follows: Mg>Ca>K>N>P. On one hand, the content of N,P,K,Cu,Zn,Cr and Pb around root system of Hippophae rhamnoide were higher than that around root system of Morus alba; on the other hand, the content of Ca,Mg,Ni and Cr around root system of Morus alba were higher than that around root system of Hippophae rhamnoide, which indicated that the content of chemical elements were related not only to soil properties, but also to plant species living there.(4) The order of heavy metal and major elements in different organics was as follows: root and leave>bark and branch>stem. The order of content of major elements was as follows: N>Ca and Mg>P. The order of the content of heavy metal was as follows: Fe>Mn>Ni>Cu >Zn>Cr>Pb>Cd. Hippophae rhamnoide and Morus alba were all have an excellent ability to enrich N and Ni.In one word, leave was able to accumulate more major elements than other organics, and root was able to accumulate more heavy metals than other organics.(5) In the individual plant, the accumulation of major elements of Hippophae rhamnoide was larger than that of Morus alba, and the accumulation of heavy metal of Hippophae rhamnoide nearly equal to that of Morus alba All of these seems to indicate that Morus alba has a stronger ability to store nutrient elements. The order of accumulation of nutrient metal in different organics between this two speciese were the same: root>leave>bark >branch>stem.(6) In the Hippophae rhamnoide and Morus alba mixed plantation, the total storage of five elements was 277.65 kg/hm~2 . The order of biomass in different layers was as follows: tree layer>litter layer>herb layer. The reason for this phenomenon is that the density and biomass of Hippophae rhamnoide were all higher than Morus alba The total storage of eight heavy metals under mixed plantation was 45.028 kg/hm~2. The order of storage of nutrient elements in different layers was as follows: litter layer>tree layer>herb layer. The storage of major elements per unit area of Hippophae rhamnoide were all higher than that of Morus alba The storage of major elements in the layer of 0~100 cm under mixed plantation was 176817.92 kg/hm~2, and total storage of N,P and K was 2076.70 kg/hm~2. The total storage of eight heavy metals was 830517.37 kg/hm~2. Fe took up 98.77 percent of total storage; Mn took up 0.96 percent of that.(7) When Hippophae rhamnoide accumulated 1 t dry matter, the content of five elements it needed was 15.144 kg, and the order of the five elements was as follows: N>Ca>Mg>K>P. When Morus alba accumulated 1 t dry matter, the content of five elements it needed was 8.181 kg, and the order of the five elements was as follows: N>Ca>K>Mg>P. When Hippophae rhamnoide and Morus alba accumulated 1 t dry matter, the total amount of eight elements was 750.59 g and 585.438 g respectively. The order of accumulation of heavy metal in different organics between this two speciese were the same: root>leave>bark>branch>stem. The order of the amount of nutrient elements two species absorbed was as follows: Fe>Mn>Ni>Cu >Zn>Cr>Pb>Cd. |
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