Insight into amelioration effect of iron-modified biochar on saline-alkali soil chemical properties and bacterial communities along a depth gradient

The application of modified biochar has been proven to be a novel and promising strategy to improve saline-alkali soil. However, the effect of iron-modified biochar (FB) on the chemical properties of saline-alkali soil at different depths remains unclear. Therefore, we designed a soil column that divides the soil into three consecutive parts to explore the amelioration effect of iron-modified biochar on saline-alkali soil chemical properties and the response of bacterial communities along a depth gradient. The results showed that soil chemical properties were significantly improved with 1% FB application, while the amelioration effect of FB was different between topsoil and subsoil. A significant increment in activities of extracellular enzymes in topsoil and decrease in base cations in subsoil were observed in 1% FB treatment. Moreover, the abundances of halophilic taxa were higher in subsoil than in topsoil, especially for the phyla Bacteroidetes and Deinococcus. Furthermore, the abundance of beneficial bacteria (e.g., Alphaproteobacteria, Sphingomonas, and Pontibacter) in saline-alkali soil increased at 1% FB. Our results suggest the influence of iron-modified biochar on soil properties and bacterial communities along a soil depth gradient, providing a novel strategy for improving saline-alkali soil with biochar.