Wood vinegar-modified biochar improves soybean growth in saline soils by enhancing soil phosphorus availability and microbial network stability

Soil microorganisms play a key role in plant adaptation to salt stress. However, how wood vinegar-modified biochars from different feedstocks regulate microbial communities and crop growth in saline soils remains unclear. In this study, biochars and wood vinegar-modified biochars prepared from maize straw and waste wood were applied at a rate of 1% (w/w) in a pot experiment. Wood vinegar modification enhanced the soil amelioration potential of biochar, but its effects were strongly feedstock-dependent. Wood vinegar-modified maize straw biochar (VMB) showed the most consistent growth-promoting effect, significantly increasing soybean biomass and nutrient uptake. Compared with maize straw biochar (MB), VMB improved soybean growth by reducing the plant Na + /K + ratio, promoting root development, enhancing microbial P turnover, increasing labile P pools, reshaping the rhizosphere microbial community, and improving microbial network stability. In contrast, wood vinegar-modified wood biochar (VWB) showed weaker and less consistent effects than wood biochar (WB). Compared with pristine biochars, wood vinegar-modified biochars had lower pH, higher dissolved organic carbon content and cation exchange capacity, and greater abundances of phenolic hydroxyl and carboxyl groups, thereby creating a more favorable soil environment for microorganisms and plants. Maize straw-derived biochar had lower pH and EC and higher specific surface area, dissolved organic carbon, total nitrogen, and available phosphorus than wood-derived biochar, which may explain its stronger response to modification. Overall, VMB promoted soybean growth by improving soil P availability and microbial network stability, providing a theoretical basis for feedstock selection and sustainable utilization of saline soils.