Wheat and maize are increasingly used as alternative crops to sunflower monocultures that dominate the Hetao Irrigation District in China.Shifts from sunflower monocultures to alternate cropping systems may have significant effects on belowground microbial communities which control nutrient cycling and influence plant productivity.In this research,rhizosphere bacterial communities were compared among sunflower,wheat and maize cropping systems by 454 pyrosequencing.These cropping systems included 2 years wheat(cultivar Yongliang 4) and maize(cultivar Sidan 19) monoculture,more than 20 years sunflower(cultivar 5009) monoculture,and wheat-sunflower and maize-sunflower rotation.In addition,we investigated rhizosphere bacterial communities of healthy and diseased plants at maturity to determine the relationship between plant health and rotation effect.The results revealed taxonomic information about the overall bacterial community.And significant differences in bacterial community structure were detected among these cropping systems.Eight of the most abundant groups including Proteobacteria,Bacteroidetes,Acidobacteria,Gemmatimonadetes,Chloroflexi,Actinobacteria,Planctomycetes and Firmicutes accounted for more than 85%of the sequences in each treatment.The wheat-wheat rhizosphere had the highest proportion of Acidobacteria,Bacteroidetes and the lowest proportion of unclassified bacteria.Wheat-sunflower cropping system showed more abundant Acidobacteria than maize-sunflower and sunflower monoculture,exhibiting some influences of wheat on the succeeding crop.Maize-maize rhizosphere had the highest proportion of γ-Proteobacteria,Pseudomonadales and the lowest proportion of Acidobacteria.Sunflower rotation with wheat and maize could increase the relative abundance of the Acidobacteria while decrease the relative abundance of the unclassified phyla,as was similar with the health plants.This suggests some positive impacts of rotation with wheat and maize on the bacterial communities within a single field.These results demonstrate that different crop rotation systems can have significant effects on rhizosphere microbiomes that potentially alter plant productivities in agricultural systems. Wheat and maize are increasingly used as alternative crops to sunflower monocultures that dominate the Hetao Irrigation District in China. Shifts from sunflower monocultures to alternate cropping systems may have significant effects on below microbial communities which control nutrient cycling and influence plant productivity. In this research, rhizosphere bacterial cells were compared among sunflower, wheat and maize cropping systems by 454 pyrosequencing. these cropping systems included 2 years wheat (cultivar Yongliang 4) and maize (cultivar Sidan 19) monoculture, more than 20 years sunflower (cultivar 5009) monoculture, and wheat-sunflower and maize-sunflower rotation. addition, we investigated rhizosphere bacterial communities of healthy and diseased plants at maturity to determine the relationship between plant health and rotation effect. The results revealed taxonomic information about the overall bacterial community. Again significant differences in bacterial community structure were detected among these cropping systems. Eight of the most abundant groups including Proteobacteria, Bacteroidetes, Acidobacteria, Gemmatimonadetes, Chloroflexi, Actinobacteria, Planctomycetes and Firmicutes accounted for more than 85% of the sequences in each treatment. wheat-wheat rhizosphere had the highest proportion of Acidobacteria, Bacteroidetes and the lowest proportion of unclassified bacteria. Wheat-sunflower cropping system showed more abundant Acidobacteria than maize-sunflower and sunflower monoculture, exhibiting some influences of wheat on the succeeding crop. Maize-maize rhizosphere had the highest proportion of γ - Proteobacteria, Pseudomonadales and the lowest proportion of Acidobacteria. Sunflower rotation with wheat and maize could increase the relative abundance of the Acidobacteria while decreasing the relative abundance of the unclassified phyla, as was similar with the health plants. This suggests some positive impacts of rotation with wheat and maize on the bacterial commu nities within a single field. these results demonstrate that different crop rotation systems can have significant effects on rhizosphere microbiomes that potentially alter plant productivities in agricultural systems.