Abiotic nitrogen immobilization affect organic matter composition and stoichiometry

Prof. Johannes Lehmann1, Leilah Krounbi1, Rachel Hestrin1, Ronald Smernik2

1Cornell University, Ithaca, United States, 2University of Adelaide, Waite, Australia

Nitrogen mineralization and immobilization are important functions of soil organic matter that affect both the availability of inorganic nitrogen for plant uptake as well as soil carbon sequestration by alleviating constraints imposed by nitrogen stoichiometry. Here we show that ammonia gas can react with soil organic matter without a biological process to form covalent carbon-nitrogen compounds. Abiotic nitrogen immobilization was greater through reactions with decomposition products and more oxidized organic matter than with plant litter. In highly oxidized organic matter, more than 10% of the nitrogen bonds formed during ammonia exposure contained heterocyclic structures. These reactions operated quickly and increased organic nitrogen contents several fold within short periods of times of second to minutes. This presentation provides evidence for abiotic immobilization as a quantitatively important and rapid reaction of inorganic nitrogen to form a variety of covalent bonds in soil organic matter. This process is highly relevant for soil fertility management as well as carbon sequestration in soil.

Biography: Johannes Lehmann, Liberty Hyde Bailey professor of soil biogeochemistry and soil fertility management at Cornell University, received his graduate degrees in Soil Science at the University of Bayreuth, Germany. During the past 20 years, he has focused on nano-scale investigations of soil organic matter, the biogeochemistry of pyrogenic carbon and sequestration in soil, and sustainable land management practices in tropical agriculture, focusing on innovative recycling of carbon and nutrients. Dr. Lehmann is a member of the steering group of the International Soil Carbon Network, has testified in the US congress, and briefed the President’s council of advisors. Dr. Lehmann has authored more than 200 journal publications, was named Highly-Cited Researcher by Thomson Reuter in 2014-2017, is member of the German National Academy of Sciences (Leopoldina) and Fellow of the Soil Science Society of America, he was named Hans-Fischer Senior Fellow of the Institute of Advanced Studies at the Technical University of Munich, and serves as editor-in-chief of the journal Nutrient Cycling in Agroecosystems.

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