Enhancing salt tolerance and growth of Oryza sativa L. through biochar-bacteria composite amendment for potential application in coastal saline soil reclamation

Abstract

Coastal saline-alkaline soils, characterized by high salinity, elevated pH, and poor physical structure, severely constrain rice productivity, and various management practices are employed to improve crop performance under saline environments. In this study, we developed a multifunctional composite (WDB@BM) by loading Bacillus mucilaginosus onto wood-vinegar-acidified diatomite-modified biochar (WDB). Incubation and pot trials using salt-tolerant Zhejingyou 1578 (ZJY 1578) and salt-sensitive Zhejingyou 4 (ZJY 4) rice varieties revealed that WDB@BM application outperformed sole amendments by decreasing soil pH, exchangeable Na⁺, and electrical conductivity (EC) while elevating cation exchange capacity (CEC) and nutrient availability. This occurred with enhanced soil enzymatic activities and alterations to the microbial community structure. Meanwhile, bacterial colonization enriched the beneficial rhizosphere microbiota, particularly Pseudomonadota and Acidobacteriota. Critically, WDB@BM significantly enhanced salt tolerance of rice ZJY 1578 by promoting Na⁺ root compartmentalization, lowering leaf Na⁺/K⁺ ratio (70.57 %), activating key antioxidant enzymes (superoxide dismutase (SOD): 72.28 %; catalase (CAT): 115.49 %), and accumulating osmolytes (proline: 63.5 %; soluble sugar: 62.9 %). Metabolomic analysis further revealed enriched nucleotide metabolism and ATP-binding cassette (ABC) transporters underpinning stress adaptation. This synergistic soil-plant-microbe modulation was particularly effective in the salt-tolerant cultivar ZJY 1578, establishing WDB@BM as a promising strategy for sustainable saline-alkali agriculture.