The patterns of macro-organisms in riverine ecosystem have been extensively explored.However,little is known about the dynamics of micro-organisms community in lotic habitat,although they play a crucial role in biogeochemical processes.Here,we conducted a comparative study in the diversity and composition patterns of archaeal and bacterial community in Kaidu River in northwestern China,to offer an insight into their distributions in riverine ecosystem.We found a marked divergence in the composition and structure between archaeal and bacterial community.For bacterial community,the α-diversity(Shannon and Pielou index)continuously increased from headwater to downriver;similarly,the β-diversity(Bray-Curtis dissimilarity)also consecutively increased along the river.Interestingly,we also observed an ecological succession between the dominant and the rare genus in composition.Statistically,the variations of bacterial community were mostly explained by temperature and spatial distance in current study.By contrast,both the diversity and composition of archaeal community were basically constant from headwater to lower reach,implicitly suggesting an idle pattern.Further,our results showed that current measured environmental parameters and spatial distance did not significantly associate with the variance in archaeal community.Nevertheless,we theoretically postulated that the high resistance was the major mechanism underlying their idle pattern.