Stoichiometric control of organic carbon–nitrate relationships from soils to the sea

• Published in: Nature (London) Vol. 464; no. 7292; pp. 1178 - 1181
• Main Authors: Taylor, Philip G, Townsend, Alan R
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.04.2010; Nature Publishing Group
• Subjects: 631/158/855; 639/638/403; 704/158/2445; Accretion; Air pollution; anabolism; Analysis; anthropogenic activities; Aquatic ecosystems; Availability; Bacteria - metabolism; Biomass; Carbon; Carbon - analysis; Carbon - metabolism; carbon nitrogen ratio; catabolism; Chemical properties; Climate; Coastal; Coastal ecosystems; Control; Creeks & streams; denitrification; Dissolved organic carbon; Earth sciences; Earth, ocean, space; Ecosystem; Ecosystems; Efficiency; Engineering and environment geology. Geothermics; Environmental aspects; Exact sciences and technology; Fabaceae; Food production; Food supply; Forecasts and trends; Fossil fuels; Fresh Water - chemistry; freshwater; Freshwater Biology; Geochemistry; Geochemistry: general, methodology, regional studies; Humanities and Social Sciences; humans; Influence; Lakes; letter; Marine Biology; Marine ecosystems; meta-analysis; Microorganisms; multidisciplinary; Natural environment; Nitrates; Nitrates - analysis; Nitrates - metabolism; Nitrification; nitrogen; Nitrogen - analysis; Nitrogen - metabolism; Nitrogen cycle; Ocean; Oceans and Seas; Plankton - metabolism; Pollution, environment geology; Properties; Ratios; Science; Seawater - chemistry; Soil - analysis; Soils; Stoichiometry; Surface water; Systematic review; Water quality; United States; sea water; stoichiometry; biomass; bacteria; accumulation; fertilizers; nitrogen; dissolution; nitrogen cycle; nitrates; human activity; agriculture; accretion; coastal zone; environment impact; prokaryotes; correlation; nitrification; ecosystems; biogenic effects; soils; fresh water; organic carbon
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/nature08985

The production of artificial fertilizers, fossil fuel use and leguminous agriculture worldwide has increased the amount of reactive nitrogen in the natural environment by an order of magnitude since the Industrial Revolution1. This reorganization of the nitrogen cycle has led to an increase in food production2, but increasingly causes a number of environmental problems1, 3. One such problem is the accumulation of nitrate in both freshwater and coastal marine ecosystems. Here we establish that ecosystem nitrate accrual exhibits consistent and negative nonlinear correlations with organic carbon availability along a hydrologic continuum from soils, through freshwater systems and coastal margins, to the open ocean. The trend also prevails in ecosystems subject to substantial human alteration. Across this diversity of environments, we find evidence that resource stoichiometry (organic carbon:nitrate) strongly influences nitrate accumulation by regulating a suite of microbial processes that couple dissolved organic carbon and nitrate cycling. With the help of a meta-analysis we show that heterotrophic microbes maintain low nitrate concentrations when organic carbon:nitrate ratios match the stoichiometric demands of microbial anabolism. When resource ratios drop below the minimum carbon:nitrogen ratio of microbial biomass4, however, the onset of carbon limitation appears to drive rapid nitrate accrual, which may then be further enhanced by nitrification. At low organic carbon:nitrate ratios, denitrification appears to constrain the extent of nitrate accretion, once organic carbon and nitrate availability approach the 1:1 stoichiometry5 of this catabolic process. Collectively, these microbial processes express themselves on local to global scales by restricting the threshold ratios underlying nitrate accrual to a constrained stoichiometric window. Our findings indicate that ecological stoichiometry can help explain the fate of nitrate across disparate environments and in the face of human disturbance.