Transformation and plant uptake of 15N-labeled fertilizers mediated by ammonia-oxidizing bacteria in alkaline bauxite-processing residue sand amended with greenwaste compost

•Bauxite residue sand (BRS) has poor nitrogen (N) content and microbial activity.•15N fate and functional genes in greenwaste compost (GC) amended BRS are examined.•GC improves 15N retention and availability of 15NO3- (dominant form of N) in BRS.•Ammonia oxidizing bacteria (AOB) is correlated with soil 15NO3- and 15N uptake.•AOB abundance and soil 15NO3- have implications for improved N management in BRS.

Ecological restoration of bauxite residue storage areas is a great challenge due to the inherently hostile characteristics (high alkalinity, high salinity and poor nutrient availability). Nitrogen (N) availability and microbial functionality are crucial indicators for successfully restoring ecosystem functions of bauxite residue storage areas. This study examined the pathway and dynamics of 15N-labeled fertilizer [e.g., ammonium sulphate (AS), potassium nitrate (KN), glycine (GL)] and the role of ammonia oxidizing archaea (AOA) and bacteria (AOB) in bauxite residue sand (BRS) amended with greenwaste compost (BRSGC) and without organic amendment (BRSNA) grown with Hardenbergia violacea and Lolium rigidum. 15N losses via volatilization and leaching from applied 15N fertilizer were higher in AS (49–50%) and GL (42–47%) compared to KN (38–44%) treatment under BRSNA. 15N losses via these pathways however, were significantly (P < 0.01) reduced under BRSGC. The total residual 15N recovered in BRSGC (34–57%) was significantly higher compared with BRSNA (<2%). Uptake of applied 15N fertilizers by plants was consistently higher in BRSNA for both plants (KN > AS > GL) compared with BRSGC, suggesting an increased sorption or immobilization of applied 15N by greenwaste compost. Significant relationships observed between the AOB abundance under AS and GL treated BRS and 15N uptake by plants and extractable 15NO3–N indicated that AOB plays a significant role in the transformation of 15N and uptake by plants. These results have important implications for developing improved nutrient management strategies and ecological rehabilitation prescriptions in alkaline BRS storage areas.