Straw incorporation alleviates salt stress in saline soils by regulating adsorption and structural evolution

Straw return is a conventional practice in mitigating soil salt damage. However, the effect of changed straw structure on the adsorption and migration of salt ions in saline soil is still unknown. This study investigated the adsorption process of straw residues at different decomposition levels. The adsorption process of straw residues towards salt ion displayed a biphasic trend with its decomposition, first increasing and then decreasing. The maximum adsorption value was 25 mg/g, representative of about 60 % decomposition rate of straw residues. This altered adsorption capacity was attributed to the balance between disruption of the dense crystalline structure and the exposure of C-O functional groups within cellulose and lignin components. The increased crystallinity index and weakened hydrogen bonding strength on the salt-adsorbing straw material surface directly confirmed the adsorption mechanisms involving pore filling and hydrogen bonding. Elevated environmental temperature (>30 °C) inhibited salt ion adsorption by straw residues. On the contrary, the adsorption of straw residues towards salt ions in the soils were independent of soluble organic and inorganic substances. Furthermore, incorporating decomposed straw residues significantly impacted soil bacterial and fungal communities. The abundance of the top 10 soil microbial taxa increased and showed a significant positive correlation with the improvements in soil structure and properties. These effects collectively alleviated salt damage symptoms during cotton seed germination and also promoted seedling growth. It demonstrated that straw return further alleviated salt damage through its structural turnover with its decomposition.