Abstract: An experiment with transgenic Bt+CpTI cotton SGK321 and its parental isoline Shiyuan 321 was conducted to examine the effects of planting transgenic Bt+CpTI cotton on the soil microbial community diversity. Rhizosphere soil was sampled at different growth stages (30, 60, 90, and 120 d) of SGK321 and Shiyuan 321. The Biolog analysis showed that the average well color development (AWCD, reflecting soil microbial activity) of all carbon sources changed in the following patterns. As compared with that for Shiyuan 321, the AWCD for SGK321 was significantly higher (P<0.05) at the growth stage of 30 d but significantly lower at other growth stages (P<0.05). The Shannon richness index and Simpson’s dominance index of the soil microbial community changed differently during the growth of SGK321 and Shiyuan 321, whereas the evenness index had no significant difference at the four growth stages of the two cultivars. Principal component analysis indicated that at the SGK321 growth stage of 30 d and the Shiyuan 321 growth stages of 60 and 120 d, and also, at the SGK321 growth stages of 60, 90, and 120 d and the Shiyuan 321 growth stage of 30 d, the carbon sources utilization of soil microbial community was similar. The main carbon sources utilized by the soil microbes were carbohydrates, amino acids, carboxylic acids, and polymers.

Key words: root order, fine root trait, seasonal dynamics, poplar plantation, productivity decline.