Abstract:Flue-cured tobacco leaves with special burnt-sweet smelling in Zimbabwe were important cigarette industrial material. It was detected that there was burnt-sweet smelling of flue-cured tobacco leaves in south Anhui Province similar to that of Zimbabwe’s in 2003. However, the forming mechanism of burnt-sweet smelling was still unknown. This paper was to explore the relationship between burnt-sweet smelling formation of flue-cured tobacco leaves in south Anhui Province and rhizosphere microorganisms. 19 soils including 7 soil types and planted 4 flue-cured tobacco variety were sampled from south Anhui Province during 2006-2007. The rhizosphere microorganism number and microbial biomass C (MBC) were analyzed in flue-cured tobacco different growth stages, i.e., rosette stage, vigorous growing stage, maturing stage and harvesting stage. The flue-cured tobacco planted in 4 representative soil types, i.e., alluvial power sandy soil, sandy loam soil in river flat, alluvial sandy loam soil and rice soil from 19 soil samples, and rhizosphere MBC of flue-cured tobacco planted in the other 15 soils from 19 soil samples were detected. The number of flue-cured tobacco rhizosphere microorganisms at rosette stage was lowest, while at vigorous growing stage was highest during tobacco growth period planted in 4 representative soil types, and subsequently it was gradually decrease in maturing and harvesting stages. Rhizosphere MBC was lowest at rosette stage but higher at vigorous growing and maturing stages of tobacco planted in 4 representative soil types, similar to the number of rhizosphere microorganisms. Rhizosphere MBC at vigorous growing stage of tobacco planted in 19 soils showed a positive linear relationship with soil organic matter and alkali hydrolyzation N significantly (p<0.01). According with the relationship, 19 soils could be divided into 3 groups, which was group I with low MBC and fertility, group II with medium MBC and fertility, group III with high MBC and fertility respectively. Flue-cured tobacco leaves with obvious burnt-sweet smelling mainly produced in 350-380 mg/kg (dry soil) of the soils belong to group II. Results indicate that rhizosphere MBC of flue-cured tobacco at vigorous growing stage was independent of tobacco variety, but only correlated with soil quality. Burnt-sweet smelling formation of flue-cured tobacco leaves related closely to rhizosphere MBC.