Enhanced elemental sulphur oxidation by the haloalkaliphilic Pseudomonas stutzeri strain 16UP4 facilitates sodic soil reclamation and enhances crop productivity

Activities of native sulphur-oxidiser communities are critical for the effective elemental sulphur (S°)–based reclamation of sodic soils. The efficiency of S°–mediated sodicity reclamation can be enhanced by enriching native soil microbial communities with efficient sulphur–oxidising microorganisms. This study reports the S°–oxidation capacity of Pseudomonas stutzeri strain 16UP4 isolated from strongly sodic soils (pH 9.9, electrical conductivity 2.4 dS m–1). Inoculation of this haloalkaliphilic strain resulted in a 21.1–37.9% increase in S° oxidation relative to uninoculated S°- treated soil at pH 9.1–10.5. This isolate produced appreciable amounts of titratable acidity, ammonia, and indole-3-acetic acid in the growth medium. It also solubilised P and Zn and formed a biofilm around S°– particles. This strain harbours the soxA, soxB, and soxY genes of 720, 590, and 329 base pairs, respectively. The enhanced S° oxidation was accompanied by a rapid decline in bicarbonate and total alkalinity, alongwith a concurrent increase in the concentrations of Ca2+, Mg2+, and PO43–. The greater oxidation of S° was also associated with a 4.6-8.0-fold decline in the sodium adsorption ratio (SARe) of the soil solution. The P. stutzeri strain 16UP4 inoculation and S° application in sodic soil increased rice and wheat yields by ~ 10–24% compared with soil treated with S° alone. This study concludes that augmenting elemental sulphur-based sodicity reclamation with P. stutzeri strain 16UP4 not only improves the efficiency of sodicity reclamation but also promotes plant growth.