Abstract: The rhizophere microbial diversities of 1，8，15 and 20-year-old Nanfeng tangerine were studied by using phospholipid fatty acid biomarkers（PLFA），respectively. The obtained results showed that the above rhizophere soils presented different characteristics in PLFA marker contents and change trends. It was observed that the microbial population（such as bacteria，sulfate-reducing bacteria，Hydrogenobacter）in relation to soil material cycling decreased with the increase of tree-age. However，the number of fungi and some of Burkholderia bacteria presented a significant increase trend，due to these microorganisms being more adaptive to poor soils and owning lower metabolic capability. Compared to the other tree-aged rhizophere soils，the total amount of PLFA of 8-year-old Nanfeng tangerine was the highest，and the PLFA of bacteria and actinomycetes also presented the highest. Although the total amount of PLFA of 20 years soil was obviously lower than other soils，its fungi PLFA was the highest. Therefore，the microbial biomass in soil was highly related with the soil fertility，and fungi were better adapted to the nutrient poor conditions compared to bacteria. Based on the community diversity indices in the rhizosphere soils between 8-year-old and 20-year-old Nanfeng tangarine，it could be concluded that the microbial community diversity and uniformity were descended with the increase of the plant year. Except invertase，the activities of urease，phosphomonesterase and peroxidase in 20-year-old rhizophere soil were all lower than those in 8-year-old rhizophere soil. The above results revealed that the PLFAs of different microbial groups had a close correlation to the soil enzyme activities and fertility factors. With the increase of plant year，the microbial community structure in rhizosphere soils occurred in a great change，which would lead to a decline of microbial diversity and an increase of the microbial groups that had low metabolic capacity and adapted to poor soil condition. Furthermore，the soil quality and the activities of some key enzymes had a significant decrease.

Key words: Citrus, rhizosphere soil, microbial community, diversity, phospholipid fatty acid biomarker