Effect of cropping systems after abandoned salinized farmland reclamation on soil bacterial communities in arid northwest China

Cropping systems are extensively used in northwest China, which alter the soil structure and nutrients, causing the changes in the soil bacterial community. Although soil bacterial communities respond differently to altered cropping systems, little is known about possible effect of cropping systems on soil bacterial communities in reclaimed soils. Using pyrosequencing-based analysis of the 16S rRNA gene, we investigated the effect of 5-year cropping systems on bacterial communities in reclaimed soils in northwest China for the first time. The three cropping systems are: maize-wheat rotation (MW), tree intercrop with cotton (TC), and monoculture cotton (MC). We have observed soil properties are obviously changed by cropping systems. The lowest soil electrical conductivity (EC), the highest aggregate stability indices (MWD and GMD) and soil organic matter (SOM) content are found in MW (P < 0.05). The dominant phyla are Firmicutes, Proteobacteria, Chloroftexi and Actinobacteria and these are present across all samples from all treatments. The highest bacterial diversity is observed in MW. The relative abundance of dominant phyla are significantly correlated EC, SOM, Fe, MWD and GMD (P < 0.05), suggesting that EC, SOM, Fe, MWD and GMD are the most important factors in shaping soil bacterial communities. Functional predictions indicate that the abundance of amino acid metabolism, carbon metabolism, glycan biosynthesis, methane metabolism, two-component and fatty acid metabolism are all enriched in MW. Overall, our study reveal that different cropping systems have different impacts not only on bacterial composition and diversity, but also on the main metabolic functions. These findings guide our future work on soil bacterial metabolic functions in different cropping systems and will provide references for salinized farmland reclamation in arid areas.