Characteristics of physiological groups of soil nitrogen-transforming microbes in different vegetation types in the Loess Gully region, China Relationship between biomass in ground and underground parts of Gentiana macrophylla and its rhizosphere microbial community structure Nitrogen removal and nitrogen-transformation bacteria in Cyperus alternifolius constructed wetland Relationship between biomass in ground and underground parts of Gentiana macrophylla and its rhizosphere microbial community structure Effects of different conservation tillage on amount and distribution of soil ammonifying bacteria, nitrobacteria and nitrogen-fixing bacteria