Recent N cycling discoveries using isotopes

September 1, 2011 – 6:07 pm

A couple of cool recent papers on N cycling, both based on isotopic data:

(1) Santoro et al. show that N2O from the ocean appears to be from ammonia-oxidizing archaea, counter to previous assumptions that it was from bacterial nitrification and denitrification:

Marine N2O sources to the atmosphere are estimated to represent ~30% of total “natural” inputs, or ~4 Tg N2O-N per year… Our results suggest that ammonia-oxidizing archaea may be largely responsible for the oceanic N2O source.

(2) Morford et al. found that plants in a Northern California forest were primarily using N from underlying rocks instead of from the usual atmospheric sources:

We report that the N content of soils and forest foliage on N-rich metasedimentary rocks (350–950 mg N kg−1) is elevated by more than 50% compared with similar temperate forest sites underlain by N-poor igneous parent material (30–70 mg N kg−1). Natural abundance N isotopes attribute this difference to rock-derived N: 15N/14N values for rock, soils and plants are indistinguishable in sites underlain by N-rich lithology, in marked contrast to sites on N-poor substrates. … Such N is primarily derived from the burial of organic matter in marine and freshwater sediments, where it is incorporated into rock as organic N or as ammonium in silicate minerals.

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