Humans dominate many important Earth system processes including the nitrogen (N) cycle. Atmospheric N deposition affects fundamental processes such as carbon cycling, climate regulation, and biodiversity, and could result in changes to fundamental Earth system processes such as primary production. Both modelling and experimentation have suggested a role for anthropogenically altered N deposition in increasing productivity, nevertheless, current understanding of the relative strength of N deposition with respect to other controls on production such as edaphic conditions and climate is limited. Here we use an international multiscale data set to show that atmospheric N deposition is positively correlated to aboveground net primary production (ANPP) observed at the 1-m2 level across a wide range of herbaceous ecosystems. N deposition was a better predictor than climatic drivers and local soil conditions, explaining 16% of observed variation in ANPP globally with an increase of 1 kg N·ha−1·yr−1 increasing ANPP by 3%. Soil pH explained 8% of observed variation in ANPP while climatic drivers showed no significant relationship. Our results illustrate that the incorporation of global N deposition patterns in Earth system models are likely to substantially improve estimates of primary production in herbaceous systems. In herbaceous systems across the world, humans appear to be partially driving local ANPP through impacts on the N cycle.
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This work was generated using data from the Nutrient Network experiment, funded at the site scale by individual researchers. Coordination and data management have been supported by funding to E. T. Borer and E. W. Seabloom from the National Science Foundation Research Coordination Network (NSF-DEB-1042132) and Long Term Ecological Research (NSF-DEB-1234162 to Cedar Creek LTER) programs, and the Institute on the Environment (DG-0001-13). We also thank the Minnesota Supercomputer Institute for hosting project data and the Institute on the Environment for hosting Network meetings. C. J. Stevens and E. M. Lind contributed equally to this work.
Appendix B and a Supplement are available online: http://dx.doi.org/10.1890/14-1902.1.sm
Stevens, Carly J.; Lind, Eric M.; Hautier, Yann; Harpole, W. Stanley; Borer, Elizabeth T.; Seabloom, Eric W.; Ladwig, Laura; Bakker, Jonathan D.; Chu, Chengjin; Collins, Scott; Davies, Kendi F.; Firn, Jennifer; Hillebrand, Helmut; La Pierre, Kimberly J.; MacDougall, Andrew; Melbourne, Brett; McCulley, Rebecca L.; Morgan, John; Orrock, John L.; Prober, Suzanne M.; Risch, Anita C.; Schuetz, Martin; and Wragg, Peter D., "Anthropogenic Nitrogen Deposition Predicts Local Grassland Primary Production Worldwide" (2015). Plant and Soil Sciences Faculty Publications. 52.
Fig. 1: Map of modeled N deposition rates at sites used in study. Circles indicate the Nutrient Network sites used in the analysis. Further details of sites are given in Appendix B: Table B1.
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Fig. 2: Standardized effect size estimates of multiscale predictors of aboveground net primary production (ANPP). Shown are probability distributions of effect of predictors on observed production (on log-linear scale) drawn from posterior distribution of multilevel model. Points are mean standardized effect estimate, thick bars are 68% credible intervals, thin bars are 95% credible intervals. Predictors with 95% credible intervals that do not include zero are considered significant effects and denoted by daggers (†). Abbreviations are PET, potential evapotranspiration; MAP, mean annual precipitation.
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Fig 3: Bivariate relationships of significant predictors. Aboveground live biomass (ANPP, measured as g/m2), shown in relation to (a) site-level atmospheric N deposition and (b) plot-level soil pH. In (a), points are modeled site mean intercept values ± SE; in (b), points are observed plot-level production. Solid lines are slopes of effects estimated from a multilevel model, estimated at the mean of other site-level predictors (e.g., N deposition effect is shown for sites at global mean MAP and PET). Dashed lines in (b) are within-site trend lines. Shaded regions depict ±SE of the slope estimates.
appendix-A.pdf (208 kB)
Anthropogenic nitrogen deposition predicts local grassland primary production worldwide: Description of hierarchical modeling process.
R_code.txt (5 kB)
R script used to implement the hierarchical model used in analysis of the relationship between grassland primary productivity and potential driver variables.