Low-release biochar for improving coastal reclaimed Saline-Alkali soil: Short-Term physicochemical responses and...

Coastal land reclamation is an important approach to expanding useable land, yet reclaimed soils are often constrained by low fertility, weak structural stability, and saline-alkaline stress. Considering traditional amendments may introduce environmental risks in sensitive coastal settings, this study evaluated the short-term responses of coastal reclaimed saline-alkali soil (Hengsha Island, Shanghai) under controlled pot conditions to a novel low-release biochar (BC-SR). Ten days after application, conventional biochar (BC-O) increased soil salinity to 2.5 times the initial level and raised pH by 0.22, whereas BC-SR exerted negligible disturbance on salinity and pH. Soil organic carbon (SOC) exhibited a net 13% reduction under BC-O during incubation, whereas BC-SR induced a 24% net rise in SOC alongside improved macroaggregate formation and microbial biomass. This effect of BC-SR further elevated the net SOC increment to 105% in the plant-containing treatments, whereas SOC decreased by 41% in the plant-only control. Exploratory metatranscriptomic analysis indicated that the treatment combining plant and BC-SR was associated with higher transcript abundances of genes related to the Calvin-Benson-Bassham cycle and other carbon fixation pathways. Overall, these findings provide short-term evidence that low-release biochar could reduce release-related risk signals while increasing soil organic carbon and improving fertility properties in reclaimed coastal saline-alkali soils under controlled pot conditions.