Linking Carbon Saturation Concepts to Nitrogen Saturation and Retention |
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Authors: | Michael J Castellano Jason P Kaye Henry Lin John P Schmidt |
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Institution: | (1) Department of Agronomy, Iowa State University, 2101 Agronomy Hall, Ames, Iowa 50011, USA;(2) Department of Crop and Soil Sciences, The Pennsylvania State University, 116 ASI Building, University Park, Pennsylvania 16802, USA;(3) USDA-ARS PSWRMU, University Park, Pennsylvania 16802, USA |
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Abstract: | Recent advances in soil C saturation concepts have increased our understanding of soil C storage and mineralization without
explicit links to N retention and saturation theories. Here, we exploit soil texture and organic matter (OM) gradients in
a Maryland, USA hardwood forest to test hypotheses that link soil organic C saturation with soil 15N retention and nitrification. At our site, mineral-associated OM (MAOM) N concentrations in the silt + clay particle fraction
(g MAOM-N g silt + clay−1) were negatively correlated with the fraction of NH4-N transferred to MAOM during a 3-day in situ incubation (R = −0.85), but positively correlated with potential net nitrification (R = 0.76). Moreover, the fraction of NH4-N transferred to MAOM was negatively correlated with potential net nitrification (R = −0.76). Due to physico-chemical stabilization mechanisms, MAOM is considered to be resistant to mineralization. Carbon
saturation theory suggests that the proportion of new C inputs that can be stabilized in MAOM decreases in proportion to the
amount of C already present in the fraction; C inputs not stabilized in MAOM are susceptible to rapid mineralization. We demonstrate
that NH4-N stabilization in MAOM is similar to C stabilization in MAOM and associated with nitrification, thereby extending soil C
saturation theory to mineral N and linking it with N retention and saturation theories. These data and concepts complement
N saturation models that emphasize vegetation type, N input levels, and microbial turnover. Incorporating the OM retention
capacity of fine mineral particles into N saturation theory can improve predictions of N saturation rates and resolve inconsistent
relationships between soil organic matter, texture, N mineralization, and N retention. |
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