Contrasting Response Patterns of Rice Phyllosphere Bacterial Taxa to Elevated CO2

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 CO2 (eCO(2)) in a rice field of a free-air CO2 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 CO2 (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.