Biochar-Mediated Microbial Mechanisms in Saline–Alkali Soils: Insights from Functional Genes and Multi-Omics Evidence

Abstract

Saline–alkali stress is a growing constraint on agricultural productivity and the ecological recovery of degraded lands worldwide. Biochar has attracted sustained interest as a soil amendment because it can improve soil structure and ionic conditions while reshaping microbial habitats that underpin key ecosystem processes. However, mechanistic understanding remains fragmented, particularly regarding how biochar-driven changes in the soil microenvironment translate into predictable shifts in microbial communities, functional genes, and the recovery of carbon, nitrogen, and phosphorus cycling. This review synthesizes current knowledge on the multidimensional mechanisms by which biochar alleviates saline–alkali stress, with a particular focus on microbial community succession and functional reprogramming. Drawing on multi-omics evidence reported in the literature, we integrate insights from metagenomic, transcriptomic, and metabolomic studies to identify convergent molecular signatures associated with biochar amendment and to relate these signals to changes in enzyme activities, nutrient availability, greenhouse-gas dynamics, and crop performance across saline–alkali settings. By connecting biochar properties and soil physicochemical amelioration with microbe-mediated biogeochemical outcomes, we propose an integrated mechanistic framework that helps explain when biochar promotes a transition from stress-adapted, low-function microbial states to more resilient and metabolically efficient communities. Finally, we highlight priorities for future research, including long-term field validation across contrasting saline–alkali soil types, harmonized multi-omics workflows and metadata standards that enable robust cross-study synthesis, and experimental strategies that move beyond correlation to causal testing of key taxa, pathways, and gene networks to improve predictability and guide biochar design and application in heterogeneous landscapes.