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

Abstract

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 and divided it into three consecutive parts (i.e., topsoil, middle soil, and subsoil) to explore the amelioration effects of biochar on saline-alkali soil chemical properties and bacterial communities along a depth gradient in the treatments amended with 0.5% (weight/weight) pristine biochar (PB), 1% (weight:weight) PB, 0.5% (weight:weight) FB, and 1% (weight:weight) FB and without biochar (control, CK). The results showed that soil chemical properties were significantly improved with 1% FB application, while the amelioration effect of FB was different between the topsoil and subsoil. The activities of extracellular enzymes significantly increased in the topsoil and base cations decreased in the subsoil in the FB treatment compared with CK. Moreover, the abundances of halophilic taxa were higher in the subsoil than in the topsoil, especially for Bacteroidetes and Deinococcota. Furthermore, the abundances of beneficial bacteria (e.g., c_Alphaproteobacteria, Sphingomonas, and Pontibacter) in saline-alkali soil increased in the FB treatment compared with CK. Our results suggest the ameliorative effect of FB on soil properties and bacterial communities along a soil depth gradient, providing a novel strategy for improving saline-alkali soil with biochar.