Allison L. Gill, Peter B. Adler, Elizabeth T. Borer, Christopher R. Buyarski, Elsa E. Cleland, Carla M. D’Antonio, Kendi F. Davies, Daniel S. Gruner, W. Stanley Harpole, Kirsten S. Hofmockel, Andrew S. MacDougall, Rebecca L. McCulley, Brett A. Melbourne, Joslin L. Moore, John W. Morgan, Anita C. Risch, Martin Schütz, Eric W. Seabloom, Justin P. Wright, Louie H. Yang, Sarah E. Hobbie
1. To evaluate how increased anthropogenic nutrient inputs alter carbon cycling in grasslands, we conducted a litter decomposition study across 20 temperate grasslands on three continents within the Nutrient Network, a globally distributed nutrient enrichment experiment
2. We determined the effects of experimental nitrogen (N), phosphorus (P), and potassium plus micronutrient (Kμ) additions on decomposition of a common tree leaf litter in a long-term study (maximum of 7 years; exact deployment period varied across sites). The use of higher-order decomposition models allowed us to distinguish between effects of nutrients on early- versus late-stage decomposition.
3. Across continents, addition of nitrogen (but not other nutrients) accelerated early-stage decomposition and slowed late-stage decomposition, increasing the slowly decomposing fraction by 28% and the overall litter mean residence time by 58%.
4. Synthesis. Using a novel, long-term cross-site experiment, we found widespread evidence that nitrogen enhances the early stages of aboveground plant litter decomposition across diverse and widespread temperate grassland sites, but slows late-stage decomposition. These findings were corroborated by fitting the data to multiple decomposition models and have implications for nitrogen effects on soil organic matter formation. For example, following nitrogen enrichment, increased microbial processing of litter substrates early in decomposition could promote production and transfer of low molecular weight compounds to soils, and potentially enhance stabilization of mineral-associated organic matter. By contrast, by slowing late-stage decomposition, nitrogen enrichment could promote particulate organic matter (POM) accumulation. Such hypotheses deserve further testing.
Journal of Ecology