Article

Nitrogen Mineralization: Challenges of a Changing Paradigm

Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Santa Barbara, California, United States
Ecology (Impact Factor: 5). 03/2004; 85(3):591–602. DOI: 10.1890/03-8002

ABSTRACT Until recently, the common view of the terrestrial nitrogen cycle had been driven by two core assumptions—plants use only inorganic N and they compete poorly against soil microbes for N. Thus, plants were thought to use N that microbes ‘‘left over,’’ allowing the N cycle to be divided cleanly into two pieces—the microbial decomposition side and the plant uptake and use side. These were linked by the process of net mineralization. Over the last decade, research has changed these views. N cycling is now seen as being driven by the depolymerization of N-containing polymers by microbial (including mycorrhizal) extracellular enzymes. This releases organic N-containing monomers that may be used by either plants or microbes. However, a complete new conceptual model of the soil N cycle needs to incorporate recent research on plant–microbe competition and microsite processes to explain the dynamics of N across the wide range of N availability found in terrestrial ecosystems. We discuss the evolution of thinking about the soil N cycle, propose a new integrated conceptual model that explains how N cycling changes as ecosystem N availability changes, and discuss methodological issues raised by the changing paradigm of terrestrial N cycling.

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    • "Ellenberg indicator values for nitrogen are based on the ordinal classification of plants in a community according to their nutritional requirements, indicating the long-term nitrogen availability of the local ecosystem (Ellenberg et al., 1992). Ellenberg N has been observed to correlate more with plant productivity than with soil N (Schaffers and Sykora, 2000), most likely because the availability of soil N to plants is affected by other soil factors and microbial activity (Schimel and Bennett, 2004) and is generally known to show temporal variability through leaching. Because of this Ellenberg N is considered to be indicative of long-term N availability rather than contemporary N availability (Rowe et al., 2011). "
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    • "Features suggesting higher decomposition rate in RT are both the slightly higher Cmic and higher content of NH + 4 -N relative to NO − 3 -N although measured just once (Table 1). In ecosystems where mineralization dominates, NH + 4 is often the dominant N species (Schimel and Bennett, 2004). Also, the high densities of L. terrestris may have directly and indirectly accelerated the decomposition in RT, particularly that of the surface residues, through the efficient consumption and incorporation of straw (Bohlen et al., 1997). "
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