Acclimation improves earthworm functions for saline-alkali soil restoration

Enhancing earthworm tolerance to soda saline-alkali soils is important for applying soil-fauna-based, nature-based approaches to restore degraded agroecosystems. Here, we produced saline-alkali tolerant earthworms (“Da Ping No. 2”, Eisenia fetida ) through directed within-generation acclimation and tested their performance, together with agricultural wastes (straw and cow dung), in an organic-amended soda saline-alkali soil microcosm. After 6 weeks of acclimation in 70% soda saline-alkali soil, earthworm survival and mean body mass increased by 56.6% and 56.0%, respectively, indicating improved fitness under stress. In an 8-week soil microcosm, saline-alkali acclimated earthworms reduced water-soluble salts (up to 23.5%) and sodicity indices (ESP decreased by 15.19%), while increasing cation buffering capacity (CEC increased by 249.77%) and optimized the composition of soil aggregates (greater proportion of > 0.053 mm aggregates). Soil fertility also improved, with available P, available K and alkali-hydrolysable N increasing by 7.50, 19.24 and 2.49-fold relative to the control. These soil shifts coincided with enhanced antioxidant responses in earthworms (CAT peaked at 5.63 U /min·mg protein at week 6) and a marked turnover of gut microbiota, including enrichment of taxa such as Saccharimonadales and Nitrospirae . Collectively, our results provide a proof-of-concept that acclimation-enabled earthworms, especially when paired with organic amendments, can promote favorable shifts in selected physicochemical properties and aggregate-size distribution in organic-amended soda saline-alkali soil microcosms, with microbiome and antioxidant adjustments co-occurring with enhanced soil nutrient cycling and aggregate stabilization.