A vast number of microorganisms colonize the leaf surface of terrestrial plants,known as the phyllosphere,and these microorganisms are thought to be of critical importance in plant growth and health.However,the taxonomic identities and ecological functions of the microorganisms inhabiting the rice phyllosphere remain poorly understood.Using a massive,parallel pyrosequencing technique,we identified the phyllosphere bacterial taxa of four different rice varieties and investigated the microbial response to elevated CO_2(eCO_2)in a rice field of a free-air CO_2 enrichment(FACE) facility located in Jiangsu Province,China.The results showed that the dominant phylotype,the Enterobacteriaceae family of Gammaproteobacteria,accounted for 70.6%-93.8%of the total bacterial communities in the rice phyllosphere.The dominant phylotype was stimulated by eCO_2,with its relative abundance increasing from 70.6%-75.2%at ambient CO_2(aCO_2) to 86.5%-93.8%at eCO_2 in the phyllosphere of rice varieties IIYou084(TY-084),YangLiangYou6(YLY-6),and ZhenXian96(ZX-96).The rare phylotypes,including the bacterial taxa of Sphingobacteriaceae,Xanthomonadaceae,Oxalobacteraceae,Clostridiaceae,and Pseudomonadaceae,were suppressed and their relative abundance decreased from 13.4%-23.0%at aCO_2 to 1.47%-6.11%at eCO_2.Furthermore,the bacterial diversity indices decreased at eCO_2 in the phyllosphere of the rice varieties TY-084,YLY-6,and ZX-96.In contrast,an opposite response pattern was observed for the rice variety of YangDao8(YD-8).In the phyllosphere of this variety,the relative abundance of the dominant phylotype,Enterobacteriaceae,decreased from 94.1%at aCO_2 to 81.4%at eCO_2,while that of the rare phylotypes increased from 3.37%to 6.59%.In addition,eCO_2 appeared to stimulate bacterial diversity in the rice variety YD-8.Our results suggest that the phyllosphere microbial response to eCO_2 might be relative abundance-dependent in paddy fields. A vast number of microorganisms colonize the leaf surface of terrestrial plants, known as the phyllosphere, and these microorganisms are thought to be critical importance in plant growth and health. Host, the taxonomic identities and ecological functions of the microorganisms inhabiting the rice phyllosphere remain poorly understood. Using a massive, parallel pyrosequencing technique, we identified the phyllosphere bacterial taxa of four different rice varieties and investigated the microbial response to elevated CO 2 (eCO_2) in a rice field of a free-air CO_2 enrichment (FACE) facility located in Jiangsu Province, China. The results showed that the dominant phylotype, the Enterobacteriaceae family of Gammaproteobacteria, accounted for 70.6% -93.8% of the total bacterial communities in the rice phyllosphere. The dominant phylotype was stimulated by eCO_2, with its relative abundance increasing from 70.6% -75.2% at ambient CO_2 (aCO_2) to 86.5% -93.8% at eCO_2 in the phyllosphere of rice varieties IIYou The rare phylotypes, including the bacterial taxa of Sphingobacteriaceae, Xanthomonadaceae, Oxalobacteraceae, Clostridiaceae, and Pseudomonadaceae, were suppressed and their relative abundance were decreased from (TY-084), YangLiangYou6 (YLY- 13.4% -23.0% at aCO_2 to 1.47% -6.11% at eCO_2.Furthermore, the bacterial diversity indices decreased at eCO_2 in the phyllosphere of the rice varieties TY-084, YLY-6, and ZX-96. In contrast, an opposite response pattern was observed for the rice variety of YangDao8 (YD-8). In the phyllosphere of this variety, the relative abundance of the dominant phylotype, Enterobacteriaceae, decreased from 94.1% at aCO_2 to 81.4% at eCO_2, while that of the rare phylotypes increased from 3.37% to 6.59% .In addition, eCO_2 had to stimulate bacterial diversity in the rice variety YD-8.Our results suggest that the phyllosphere microbial response to eCO_2 might be relative abundance-dependent in paddy fields.