Response of phyllosphere bacterial communities to elevated CO2 during rice growing season

The phyllosphere, the aerial parts of terrestrial plants, represents the largest biological interface on Earth. This habitat is colonized by diverse microorganisms that affect plant health and growth. However, the community structure of these phyllosphere microorganisms and their responses to environmental changes, such as rising atmospheric CO2, are poorly understood. Using a massive parallel pyrosequencing technique, we investigated the feedback of a phyllosphere bacterial community in rice to elevated CO2 (eCO2) at the tillering, filling, and maturity stages under nitrogen fertilization with low (LN) and high application rates (HN). The results revealed 9,406 distinct operational taxonomic units that could be classified into 8 phyla, 13 classes, 26 orders, 59 families, and 120 genera. The family Enterobacteriaceae within Gammaproteobacteria was the most dominant phylotype during the rice growing season, accounting for 61.0-97.2 % of the total microbial communities. A statistical analysis indicated that the shift in structure and composition of phyllosphere bacterial communities was largely dependent on the rice growing stage. eCO2 showed a distinct effect on the structure of bacterial communities at different growth stages, and the most evident response of the community structure to eCO2 was observed at the filling stage. eCO2 significantly increased the relative abundance of the most dominant phylotype (Enterobacteriaceae) from 88.6 % at aCO2 (ambient CO2) to 97.2 % at eCO2 under LN fertilization at the filling stage, while it significantly decreased the total relative abundance of other phylotypes from 7.48 to 1.35 %. Similarly, higher value for the relative abundance of the most dominant family (Enterobacteriaceae) and lower value for the total relative abundance of other families were observed under eCO2 condition at other growth stages and under different N fertilizations, but the difference was not statistically significant. No consistent response pattern was observed along growth stages that could be attributed to N treatments. These results provide useful insights into our understanding of the response of a phyllosphere bacterial community to eCO2 with regards to the diversity, composition, and structure during rice growing seasons.