Dissimilatory nitrate reduction to ammonium and N sub(2)O flux: effect of soil redox potential and N fertilization in loblolly pine forests

• Published in: Biology and fertility of soils Vol. 52; no. 5; pp. 601 - 614
• Main Authors: Minick, K J, Pandey, C B, Fox, T R, Subedi, Santosh
• Format: Journal Article
• Language: English
• Published: 01.07.2016
• ISSN: 0178-2762; 1432-0789
• DOI: 10.1007/s00374-016-1098-4

Nitrogen (N) fertilization and soil redox potential influence N cycling processes in forested ecosystems. Gross N transformations are indicators of NH sub(4) super(+) and NO sub(3) super(-) production and consumption within soil. Furthermore, dissimilatory nitrate reduction to ammonium (DNRA), a typically overlooked process in terrestrial N cycling, can conserve N within soil by reducing losses of soil N via NO sub(3) super(-) leaching and denitrification. We tested the effects of urea fertilization and soil redox on microbial N cycling processes and N sub(2)O fluxes using a super(15)N tracer experiment in soils from loblolly pine plantations located in different physiographical regions (i.e., Coastal Plain of North Carolina and Piedmont of Virginia). Mineral soils (0-15 cm) from fertilized and unfertilized plots were incubated at high (Eh, 200 to 400 mV) and low redox potential (Eh, -100 to 100 mV). Site differences were limited primarily to edaphic factors, although gross N mineralization was higher in NC. Gross nitrification, DNRA, and NO sub(3)- super(-)-N concentrations were higher in soils from fertilized plots. DNRA was higher at high compared to low redox potential, while N sub(2)O fluxes were higher at low redox potential. Fluxes of N sub(2)O were further enhanced in fertilized treatments incubated at low redox potential. DNRA was positively correlated with NO sub(3) super(-) availability, but not to soil C pools. Furthermore, DNRA was negatively correlated with C/NO sub(3) super(-) ratio, implying that NO sub(3) super(-) pool size was the primary factor influencing DNRA. These results suggest N fertilization has alleviated limitations to nitrification, DNRA, and N sub(2)O production processes and that gaseous losses of N will prevail over N conservation pathways at low soil redox potentials.