Abstract: Conservation tillage has beneficial effects on soil microbes, but the effects on soil photosynthetic bacteria and methanotrophs are rarely reported. In this study, denaturing gel gradient electrophoresis (DGGE) and quantitative PCR technique were adopted to investigate the abundance and community structure of photosynthetic bacteria and type Ⅱ methanotrophs in a fluvoaquic soil as affected by different tillage modes (no-tillage and conventional tillage) and straw mulching (0, 50%, 100%). Under no tillage, the diversity of soil photosynthetic bacteria was significantly higher but the abundance was slightly lower, as compared with those under conventional tillage, and there was a significant positive correlation between the diversity of soil photosynthetic bacteria and the soil total nitrogen. Both the abundance and the diversity of soil photosynthetic bacteria had a trend of increased with increasing amount of straw mulch. Tillage, straw mulching, and their interaction also had definite beneficial effects on the abundance and diversity of type Ⅱ methanotrophs. In all treatments, the community structure of soil photosynthetic bacteria and type Ⅱ methanotrophs had less change. The dominant groups of soil photosynthetic bacteria were Rhizobiales and Sphingomonadales, and that of type Ⅱ methanotrophs was Methylocystaceae.

Key words: rhizosphere effect, soil nutrient, soil microbe, Stipa grandis, typical steppe.