Kandelia obovata afforestation enhances coastal soil quality over Spartina alterniflora invasion but increases phosphorus limitation

This study evaluated 0–100 cm soil properties among native Carex scabrifolia , invasive Spartina alterniflora , restored Kandelia obovata , and mixed stands of K . obovata and S . alterniflora in Oujiang Estuary, and among four K . obovata restoration sites in Zhejiang Province, China. Results showed vegetation type and soil depth significantly influenced soil properties. K . obovata soils displayed the lowest C:N and highest N:P ratios, total nitrogen, and available phosphorus among vegetation types, suggesting nitrogen sufficiency but phosphorus limitation. Soil attributes in K . obovata forests varied significantly by location and soil depth. Principal-component analysis ranked vegetation types as K . obovata > S . alterniflora > mixed stands> C . scabrifolia ; and K . obovata sites as Yanpu Bay > Ximen Island > Oujiang Estuary > Dongshan Wharf. Therefore, K . obovata afforestation enhances soil quality, with Yanpu Bay and Ximen Island as optimal restoration areas. Restoration increases phosphorus demand, necessitating targeted supplementation for long-term ecosystem health.