Vermicompost enhances the salt tolerance of maize by reshaping the rhizosphere microenvironment

Vermicompost can improve saline soil by alleviating soil salinity, forming soil aggregates and regulating nutrient cycling, however, the mechanisms underlying its effects on the rhizosphere microenvironment and plant salt tolerance have not been elucidated. This study examined the ability of vermicompost to improve the macroaggregate microstructure, soil microbial community and nitrogen mineralization in the rhizosphere, which consequently improved maize salt tolerance in saline soil. Transcriptomic, metabonomic, synchrotron radiation-based micro-computed tomography and ¹⁵N tracer techniques were used to elucidate the underlying mechanisms involved. The results indicated that vermicompost application reshaped the macroaggregate microstructure and soil bacterial community, decreased the soil salinity (5.6 %) and increased ¹⁵N mineralization (33 %) of the wheat straw in the saline soil. Moreover, vermicompost affected the expression of salt tolerance genes and citrate cycle activity, and increased ¹⁵N-NO₃⁻ uptake (64 %) by the roots, in turn increasing the growth of maize roots (38 %). In maize shoots, vermicompost induced stomatal closure, regulated photosynthesis, modulated the ABA-activated signalling pathway and activated amino acid metabolism by doubling nitrogen uptake to almost double the growth of the shoots. Collectively, these findings greatly enhance the understanding of the mechanisms underlying the physiological response of plants to improvements in the rhizosphere microenvironment and provide innovative concepts for ensuring food security and promoting agricultural productivity in saline soil.