DOI: 10.5061/dryad.vdncjsz50
title: Data from: Interactions among nutrients govern the global grassland biomass, precipitation relationship

description: Ecosystems are experiencing changing global patterns of mean annual
 precipitation (MAP) and enrichment with multiple nutrients that
 potentially co-limit plant biomass production. In grasslands, mean
 aboveground plant biomass is closely related to MAP, but how this
 relationship changes after enrichment with multiple nutrients remains
 unclear. We hypothesized the global biomass-MAP relationship becomes
 steeper with an increasing number of added nutrients, with increases in
 steepness corresponding to the form of interaction among added nutrients
 and with increased mediation by changes in plant community diversity. We
 measured aboveground plant biomass production and species diversity in 71
 grasslands on six continents representing the global span of grassland
 MAP, diversity, management, and soils. We fertilized all sites with
 nitrogen, phosphorus, and potassium with micronutrients in all
 combinations to identify which nutrients limited biomass at each site. As
 hypothesized, fertilizing with one, two, or three nutrients progressively
 steepened the global biomass-MAP relationship. The magnitude of the
 increase in steepness corresponded to whether sites were not limited by
 nitrogen or phosphorus, were limited by either one, or were co-limited by
 both in additive, or synergistic forms. Unexpectedly, we found little
 evidence for mediation of biomass–MAP relationships by plant community
 diversity because relationships of species richness, evenness and beta
 diversity to MAP and to biomass were weak or opposing. Site-level
 properties including baseline biomass production, soils, and management
 explained little variation in biomass-MAP relationships. These findings
 reveal multiple nutrient co-limitation as a defining feature of the global
 grassland biomass-MAP relationship.
description: Data were collected from 71 sites distributed across six
 continents.  Data were collected by individual site investigators using
 the standardized Nutrient Network
 Protocol. Investigators submit site data to the network manager
 who performs internal processing and quality control to build datasets. 
 For this dataset, processing and analysis were performed in SAS and a code
 package has been included. In summary, data were error-checked and
 gap-filled as described in the publication.
description: # Data from: Interactions among nutrients govern the global grassland
 biomass – precipitation relationship
 [https://doi.org/10.5061/dryad.vdncjsz50](https://doi.org/10.5061/dryad.vdncjsz50) PI: Philip Fay, USDA-ARS Grassland, Soil, and Water Research Laboratory, Temple, TX 76502 USA. ## Description of the data and file structure Data collected: Data are from 71 grassland sites which conducted a multiple nutrient fertilization experiment for a minimum of 4 and a maximum of 14 years. All sites followed the Nutrient Network standardized experimental protocol. 5 m x 5 m experimental plots were fertilized nitrogen, phosphorus, or potassium in factorial combinations with at least three replicates per nutrient combination. Current year live aboveground biomass was sampled by harvesting, and plant community composition was measured by visual estimates of the percent cover of each plant species. Protocol details are available at [www.nutnet.org](http://www.nutnet.org) and in (1). Location of data collection: 71 sites on six continents. Site latlongs are included in the site_year_means dataset. Date of file creation: 1st draft 14 January 2025 03 December 2020 Licenses or restrictions: none Missing value designation: empty cells. ### Files and variables Metadata Tab: Column A: A combined list of variable names used across the two datasets site_means and site_year_means. Column B: Descriptions of the variables named in column A. Site_means Tab: Treatment means and standard errors of live_mass, effective species richness, Evenness,and plot_beta by site, averaged across years. Variable names defined in the metadata tab. Missing values (empty cells) occur in the soils variables (pct_N, ppm_P, ppm_K, PercentSand, PercentSilt, PercentClay) in two cases: 1) no data were provided for a site or 2) for the texture variables, data were collected only from control plots. Site_year_means Tab: Treatment means and standard error (SE) of live_mass, and number of reps by site and year. Variable names defined in the metadata tab. Version Changes 02 April 2025: Uploaded files containing SAS code used to perform the analysis and make the graphics used in this paper. Files containing SAS code have the .sas extension, and the filename begins with a number indicating the order in which the code in the files should be run. The datafile Fay_PNAS_01142025 was not revised in this update.   Notes on the code files 1_libnames_options_varlists.sas: assigns library locations, creates variable lists, and sets certain SAS options. Beware that editing the variable lists will alter output from nearly every following program. 2_Read_NutNet.sas: Reads the raw dataset obtained from the Nutrient Network and performs some initial processing. 3_impute_and_clean.sas: Performs data cleaning and imputation steps as described in the published SI_Appendix. 4_build_precip.sas: Assembles precipitation data sets for joining with the raw dataset. 5_build dataset: joins the precipation dataset to the raw dataset, selects sites and observations meeting inclusion criteria, aligns precipitation years with biomass years, cross-validates the various precipitation data sources, produces the datasets used in subsequent analyses. 6_site nut effects LSM meth.sas: Fits a linear mixed model to each site, produces least square means and their p-values for use in the rubric assigning sites to the categories of nutrient limitation. The code is written to for interactions for N and P but can be modified to test other pairs of nutrients. 7_compute graph means: generates means and standard errors organized for graphing in OriginPro. 8_export graph means: Writes excel files containing the datasets produced in the preceding code file. 9_sitelist_table.sas: Produces Table S1 in the SI Appendix. 10_Mixed trts precip and temp vars: Fits various linear mixed models testing 1) which climate variables yield best fit to biomass across sites, 2) how many and which nutrients limit or co-limit biomass and influence plant species diversity variables. 11_export mixed trts tables: Writes excel files containing results from the mixed models analyses. 12_Mixed NP forms.sas: Fits linear mixed models across sites within four forms of nutrient limitation, and related sub-analyses. 13_Export mixed NPforms tables.sas: Writes an excel file used as Table S6 in SI Appendix. 14_Mgmt & Soils.sas: Fits models testing whether the classified sites differ in management, soils, and other site-level properties. 15_SEMs.sas: Fits the structural equation models and produces output tables. Literature Cited: 1. E. T. Borer et al., Finding generality in ecology: a model for globally distributed experiments. Methods Ecol. Evol. 5, 65-73 (2014).