Inhibition of nitrification alters carbon turnover in the Patagonian steppe

A. T. AUSTIN; O. E. SALA; R. B. JACKSON

ECOSYSTEMS (NEW YORK. PRINT)

Springer

Año: 2006 vol. 9 p. 1257 - 1265

1432-9840

Human activities are altering biodiversity and the N cycle, affecting terrestrial carbon cycling globally.  Only a few specialized bacteria carry out nitrification, the transformation of ammonium to nitrate, in terrestrial ecosystems, which determines the form and mobility of inorganic N in soils. However, the control of nitrification on carbon cycling in natural ecosystems is poorly understood.  Here, we report results from an ecosystem experiment in the Patagonian steppe where we inhibited autotrophic nitrification and measured its effects on C and N cycling.  Decreased net nitrification increased total mineral N and NH4+ and reduced NO3- in the soil.  Plant cover (P < 0.05) and decomposition (P < 0.0001) decreased with inhibition of nitrification, in spite of increases in NH4+ availability. Significant changes in the natural abundance of d15N in dominant vegetation with nitrification inhibition suggest that there was a switch in the form of nitrogen (from NO3- to NH4+) taken up by plants, and results from a controlled-condition experiment support the field results that the dominant plant species of the Patagonian steppe have a marked preference for nitrate. Our results highlight that nitrifying bacteria exert a major control on ecosystem functioning, and that the inhibition of nitrification resulted in significant alteration of the C cycle. The interactions between the C and N cycles suggest that rates of C cycling are not just affected by the amount of available N, but also by the relative availability of NH4+ to NO3- available for plant uptake.