Synergistic Effects of modified Halophytes-derived biochar on Carbon Sequestration, Soil Amelioration, and Alfalfa Productivity in Saline-Alkali Soil

Biochar is a stable carbon source with promising applications in soil improvement and carbon sequestration; however, its efficacy in saline-alkali soils is constrained by its inherent properties. In this study, a pot experiment was conducted to evaluate the effects of different application rates of pristine (BC) and modified (MBC) halophytes-derived biochar on the physicochemical properties, carbon pool composition, and growth of alfalfa in saline-alkali soil. The results showed that direct BC application inhibited alfalfa growth, whereas low application rates of MBC significantly increased alfalfa shoot dry weight. However, the high application rate of MBC still exerted inhibitory effects. The MBC effectively reduced soil pH and exchangeable sodium percentage, while significantly increasing soil organic carbon and its labile and recalcitrant fractions, enhancing soil carbon sequestration capacity. Moreover, application of modified biochar increased the relative abundance and diversity of rhizosphere soil bacteria, with shifts in community composition favoring genera associated with carbon cycling and plant growth promotion, including Sphingomonas, Streptomyces and Lysobacter. Overall, MBC enhances plant productivity while achieving carbon sequestration by improving soil physicochemical properties, promoting organic carbon accumulation, and regulating rhizosphere microbial communities, thereby offering a promising strategy for ecological restoration and carbon sink enhancement in saline-alkali soils.