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

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 N-15-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. N-15 losses via volatilization and leaching from applied N-15 fertilizer were higher in AS (49-50%) and GL (42-47%) compared to KN (38-44%) treatment under BRSNA. N-15 losses via these pathways however, were significantly (P < 0.01) reduced under BRSGC. The total residual N-15 recovered in BRSGC (34-57%) was significantly higher compared with BRSNA (<2%). Uptake of applied N-15 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 N-15 by greenwaste compost. Significant relationships observed between the AOB abundance under AS and GL treated BRS and N-15 uptake by plants and extractable (NO3)-N-15-N indicated that AOB plays a significant role in the transformation of N-15 and uptake by plants. These results have important implications for developing improved nutrient management strategies and ecological rehabilitation prescriptions in alkaline BRS storage areas. (C) 2014 Elsevier B.V. All rights reserved.