| Currently, the economical and social values of plantations have been maximized, whereas its ecological values remain being disputed. At present, the studies of biological diversity on plantation were focused on the above-ground biodiversity. Although some studies concerned with soil biota, rarely studies were carried out from the perspective of the whole ecosystem of above and, below ground eco-system. Soil microbial was an important component of the forest ecosystem, the changes of microbial was closely contacted with nutrient cycling and decomposition. Microbial activity was an important biological indicators in soil quality assessment. There are several factors influencing the soil microbe, however, little information is available for the dynamics of soil microbe with plantations ages. Consequently, Soil microbe biomass is the active component of soil microbe, which decide the capability of microbe on nutrient controlling and decomposition of organic matter. As an important component of the formation of biological diversity in Eucalypyu grandis plantation, we studied the soil microbial amount and biomass along a chronosequence(1-10aged) of Eucalypyu grandis plantation from 2007 to 2008 in Yangchang town, Danling country. The object was aimed to characterize the dynamic changes of soil microbial amount and its activity along a chronosequence of Eucalypyu grandis plantation at the same site conditions, and revealing the formation of microbial diversity. The main results showed as follows:1. In the ten Eucalypyus grandis plantations, the vertical distribution of soil microorganism at the three layers(0-10cm, 10-20cm, 20-30cm) were similar. Each physiological group of microorganism and total microbes were accumulated in the layer of 0-10cm, the numbers of microbes in the same physiological group were various. The total microbes increased from 4.56 to 11.44×106·g-1 dry weight (0～30cm) . The number of bacteria represented apparently seasonal dynamics (Autumn＞Spring＞Summer≈Winter). Fungi represent significantly seasonal dynamics (Spring＞Summer≈Winter＞Autumn). No significant seasonal dynamics were found in actinomyces. Soil microbe in E. grandis (1-10 years old) represents a "decrease-increase-stable" trend with a S shape. The lowest total number of soil microbe was pronounced in 4 year-old E. grandis with the value of 7.12×106·g-1·dry weight and reached the highest value in 10 years old with the value of 9.19×106·g-1·dry weight. The biodiversity indices of soil microbe were higher in older E. grandis (6-10 years old) than the younger ones (1-5 years old) and reached the highest level in 8 years old soil with Simpson, Shannon-wiener and pielou indices 0.148, 0.307, 0.279 respectively. 2.The vertical distribution of microbial biomass carbon and nitrogen in different aged E.grandis plantation were similar, decreased with the depth of soil layer. The varies of microbial biomass in surface layer changed more than deeper layer, and the varies of microbial biomass nitrogen (MBN )were much more than microbial biomass carbon(MBC). As E.grandis plantation grew, the soil microbial biomass carbon represented a trend as decreasing from 1- 4 years, but increasing from 4-10 years. The MBC in 4 aged E.grandis decreased 47.03% than 1 aged, but in 10 aged E.grandis, the MBC was double of 4 aged. Above all, The MBC along a range of forest ages of E.grandis increased by 8.35%. The soil microbial biomass nitrogen fluctuated repeatly but stabilized in older E.grandis. The MBN in 6 aged E.grandis decreased by 90.97% during 10 years , but in 10 aged E.grandis, the MBN was 15 times of 6 aged. Above all, The MBN in a range of forest aged E.grandis increased by 48.01%.3.Microbial factors(Bacteria/Actinomyces/Fungi/MBC/MBN) represented positive correlation with water content, organic carbon and total nitrogen, but negative correlation with pH, Total P and Available P. Bacteria correlated with Water content and Organic carbon very significant, and significant correlated with pH and Available P; Actinomyces significantly correlated with Organic carbon , and significantly correlated with pH and Available P; Fungi, MBC and MBN represented unsignificant relevance with soil nutrient factors. The microbes in soil represented positive correlation with both MBC and MBN, but among each factor, the other was no significant besides Bacteria and MBC.4.Imitated the model of soil nutrient:water content: Y1=5.032×10-15+1.472A1-0.069A2-0.071A3-0.657A4-0.165A5pH:Y2=-3.519×10-15-1.752B1+0.353B2+0.357B3+0.369B4+0.353B5organic C: Y3=1.215×10-15+0.957C1+0.174C2+0.012C3-0.282C4+0.055C5 total N:Y4=-2.754×10-15-1.448D1+0.426D2+0.609D3+0.959D4+0.442D5 total P: Y5=2.303×10-15-0.516E1-0.339E2-0.619E3+0.841E4-0.053E5available P: Y6=-7.67×10-15-1.285F1-0.076F2+0.046F3+0.575F4+0.083F5 A1-A5 presented Bacteria, Actinomyces, Fungi, MBC, MBN, the same asB1-5-F1-5MBC:Y7=2.520×10-15+1.173G1-0.460G2-0.025G3MBN:Y8=2.894×10-15+1.178H1-0.948H2-0.515H3 G1,H1-G3,H3 presented Bacteria, Actinomyces, Fungi...
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