Availability of urea to autotrophic ammonia-oxidizing bacteria as related to the fate of 14C- and 15N-labeled urea added to soil

• Published in: Biology and fertility of soils 2005-11, Vol.42 (2), p.137-145
• Main Authors: Marsh, K.L, Sims, G.K, Mulvaney, R.L
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Alkaline soils; Amino acids; Ammonium; autotrophs; Bacteria; Biochemistry and biology; Biological and medical sciences; carbon; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Geochemistry; Microbiology; Microorganisms; Nitrates; Nitrification; nitrogen; Nitrogen fertilization; Nitrogen, phosphorus, potassium fertilizations; Nitrosomonas europaea; Nitrosospira; Nutrient availability; Physics, chemistry, biochemistry and biology of agricultural and forest soils; soil bacteria; soil chemical properties; Soil microorganisms; Soil science; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Soils; stable isotopes; Urea
• ISSN: 0178-2762; 1432-0789
• DOI: 10.1007/s00374-005-0004-2

Nitrate has been found to accumulate more rapidly in soils fertilized with urea than with inorganic sources of NH^sub 4^ ^sup +^, despite the fact that nitrification must be preceded by hydrolytic decomposition. For acidic conditions, this finding has been attributed to limited uptake of NH^sub 4^ ^sup +^ by ammonium-oxidizing bacteria (also reported herein), suggesting an advantage for direct utilization of a nonionizable N substrate such as urea. If the same advantage applies to urea-C, nitrification of urea-N would also be promoted in neutral or alkaline soils, as reported in numerous studies. To ascertain whether urea-C can be utilized directly by nitrifying organisms, NO^sub 2^ ^sup -^ production was measured for Nitrosomonas europaea and Nitrosospira sp. NPAV in minimal media with urea as the sole source of either C or C and N. Nitrite accumulated only with the latter organism, in which case nearly quantitative recovery was observed for N added as NH^sub 4^ ^sup +^ and/or urea. In a subsequent study, recovery of ^sup 14^C and ^sup 15^N in gaseous, extractable, and hydrolyzable forms was determined after incubation with labeled urea for up to 29 days, by using two soils that differed markedly in physiochemical properties affecting nutrient availability. Results obtained in correlating ^sup 14^C incorporation in the amino acid fraction with ^sup 15^N accumulation as NO^sub 3^ ^sup -^ were consistent with the stoichiometry that would be expected if C fixation were driven by autotrophic nitrification. Our findings demonstrate unequivocally that urea is utilized as a source of C and N by nitrifying microorganisms, which may account for rapid nitrification of urea-N in soils.[PUBLICATION ABSTRACT]