Recycling Agricultural Waste into Plant Protectants: Mechanisms of Wood Vinegar in Alleviating Salt Stress in Triticum aestivum L.

Soil salinity severely impairs crop productivity by inducing osmotic stress, ionic toxicity, and oxidative damage. This study investigated the mechanisms by which foliar-applied wood vinegar (WV), a biomass pyrolysis byproduct rich in organic acids and minerals, alleviates salt stress (100 mM NaCl) in hydroponically grown wheat (Triticum aestivum L.). Three WV dilutions (100×, 300×, 500×) were tested to evaluate their effects on growth, antioxidant systems, chlorophyll metabolism, and ion homeostasis. The results demonstrated that 300×-diluted WV (WV3) most effectively mitigated salt stress, increasing shoot biomass by 81% and root length by 75% compared to salt-stressed controls. WV3 restored antioxidant enzyme activities to non-stressed levels, reduced lipid peroxidation, and normalized chlorophyll overaccumulation induced by salinity. Elemental profiling revealed that WV3 enhanced shoot K+ and Ca2+ uptake while reducing Na+ accumulation, thereby improving ion homeostasis. Additionally, WV3 promoted Fe translocation to shoots, supporting chlorophyll synthesis. However, 100× WV (WV1) exhibited phytotoxicity due to excessive organic acids, while 500× (WV5) showed limited efficacy. These findings highlight a 300-fold diluted solution of WV as an optimal dilution for enhancing wheat salt tolerance through coordinated ROS scavenging, photosynthetic protection, and ion regulation. This study provides a scientific basis for integrating WV into sustainable strategies to combat salinity in wheat cultivation.