Inhibition of Nitrification Alters Carbon Turnover in the Patagonian Steppe |
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Authors: | Amy T Austin Osvaldo E Sala Robert B Jackson |
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Institution: | (1) Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura (IFEVA), Facultad de Agronomía, CONICET and Universidad de Buenos Aires, Avenida San Martín 4453, Buenos Aires, C1417DSE, Argentina;(2) Department of Biology and Nicholas School of the Environment, Duke University, Durham, North Carolina 27708, USA |
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Abstract: | Human activities are altering biodiversity and the nitrogen (N) cycle, affecting terrestrial carbon (C) cycling globally.
Only a few specialized bacteria carry out nitrification—the transformation of ammonium (NH
4
+
) to nitrate (NO
3
−
), in terrestrial ecosystems, which determines the form and mobility of inorganic N in soils. However, the control of nitrification
on C cycling in natural ecosystems is poorly understood. In an ecosystem experiment in the Patagonian steppe, we inhibited
autotrophic nitrification and measured its effects on C and N cycling. Decreased net nitrification increased total mineral
N and NH
4
+
and reduced NO
3
−
in the soil. Plant cover (P < 0.05) and decomposition (P < 0.0001) decreased with inhibition of nitrification, in spite of increases in NH
4
+
availability. There were significant changes in the natural abundance of δ15N in the dominant vegetation when nitrification was inhibited suggesting that a switch occurred in the form of N (from NO
3
−
to NH
4
+
) taken up by plants. Results from a controlled-condition experiment supported the field results by showing that the dominant
plant species of the Patagonian steppe have a marked preference for nitrate. Our results indicate that nitrifying bacteria
exert a major control on ecosystem functioning, and that the inhibition of nitrification results in significant alteration
of the C cycle. The interactions between the C and N cycles suggest that rates of C cycling are affected not just by the amount
of available N, but also by the relative availability for plant uptake of NH
4
+
and NO
3
−
. |
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Keywords: | carbon cycling nitrification inhibition nitrogen mineralization semi-arid ecosystem ammonium nitrate 15N stable isotope Patagonian steppe Argentina nitrapyrin |
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