Photosynthetic assimilation of CO2 is a primary source of carbon in soil and root-exudates and can influence the community dynamics of rhizosphere organisms.-Thus, if carbon partitioning is affected in transgenic crops, rhizosphere microbial-communities may also be affected. In this study, the temporal effects of gene-transformation on carbon partitioning in rice and rhizosphere microbial communities-were investigated under greenhouse conditions using the 13C pulse-chase-labeling method and phospholipid fatty acid (PLFA) analysis. The 13C contents in-leaves of transgenic (Bt) and nontransgenic (Ck) rice were significantly different at-the seedling, booting and heading stages. There were no detectable differences in-13C distribution in rice roots and rhizosphere microorganisms at any point during-rice development. Although a significantly lower amount of Gram-positive-bacterial PLFAs and a higher amount of Gram-negative bacterial PLFAs were-observed in Bt rice rhizosphere as compared with Ck at all plant development-stages, there were no significant differences in the amount of individual 13C-PLFA-between Bt and Ck rhizospheres at any growing stage. These findings indicate that-the insertion of cry1Ab and marker genes into rice had no persistent or adverse-effect on the photosynthate distribution in rice or the microbial community-composition in its rhizosphere-