DOI: 10.5061/dryad.qrfj6q5qp
title: Data from: More diverse rhizobial communities can lead to higher symbiotic nitrogen fixation rates, even in nitrogen-rich soils

description: Symbiotic nitrogen fixation (SNF) by legumes and their rhizobial partners
 is one of the most important sources of bioavailable nitrogen to
 terrestrial ecosystems. While most work on the regulation of SNF has
 focused on abiotic drivers such as light, water, and soil nutrients, the
 diversity of rhizobia with which an individual legume partners may play an
 important but under-recognized role in regulating nitrogen inputs from
 SNF. By experimentally manipulating the diversity of rhizobia available to
 legumes, we demonstrate that rhizobial diversity can increase average SNF
 rates by more than 90%, and that high rhizobial diversity can induce
 increased SNF even under conditions of high soil N fertilization. However,
 the effects of rhizobial diversity, the conditions under which diversity
 effects were strongest, and the likely mechanisms driving these diversity
 effects differed between the two legume species we assessed. These results
 provide evidence that biodiversity-ecosystem function relationships can
 occur at scales of an individual plant, and that the effects of rhizobial
 diversity may be as important as long-established abiotic factors, such as
 nitrogen availability, in driving terrestrial nitrogen inputs via SNF.
description: Data were collected from a greenhouse experiment conducted at the
 Smithsonian Environmental Research Center in 2019. Two legume species
 (<em>Spartium junceum</em> and <em>Ulex</em>
 <em>europaeus</em>) were exposed to different levels of
 rhizobial diversity (0 to 5 rhizobial taxa) and different levels of
 nitrogen fertilization (0 to 20 g/m2/yr). Data represent biomass, biomass
 allocation, and nitrogen fixation metrics measured on 1100 plants
 following a five-month growth period.
description: # More diverse rhizobial communities can lead to higher symbiotic nitrogen
 fixation rates, even in nitrogen-rich soils
 [https://doi.org/10.5061/dryad.qrfj6q5qp](https://doi.org/10.5061/dryad.qrfj6q5qp) ## Description of the data and file structure This repository contains three files with data and corresponding code related to a greenhouse experiment where two legume species were exposed to different treatments of nitrogen fertilization and rhizobial diversity. Numerous metrics of plant growth and nitrogen fixation were measured. The "biomass" data file contains biomass data on all ~1,100 plants in the experiment. The "Nfix data" file contains data on the subset of individuals in each treatment that were sent for 15N isotopic analysis to calculate N fixation at the end of the experiment. The R code file requires both data files to run completely.  #### Data File 1: Rhizdiv\_postprocess\_biomass\_data\_1-2023.csv This file contains biomass data for all 1100 plants in the experiment. Percent foliar N and atom % 15N data are available for the subset of plants used to estimate nitrogen fixation. Missing data code- NA Position: Unique position in the greenhouse (1-1100) Pot: Unique Plant Identifier Species: Legume species. UE = Ulex europaea, SJ = Spartium junceum fert: Fertilization treatment in g/m2/yr N delivered as ammonium nitrate div: Diversity (taxa richness) of rhizobial bacteria used to innoculate the plant (C=no rhizobia Inoculum) bac: The identities of the rhizobia used to inoculate the plants harvest.date: Date the plant was harvested at the end of the experiment stem.biomass: biomass of all aboveground tissue (g) root.biomass: biomass of all belowground tissue (g) nodule.number: number of individual nodules found on the entire root system Rack..: Rack number where the plant's pot was held in the greenhouse.  Observer: Initials of the researcher harvesting the individual plant fert.num: Numeric variable for the fertilization treatments div.num: Numeric variable for the rhizobial diversity treatments tot.biomass: total biomass of the entire plant (g) agbg: aboveground to belowground biomass ratio (unitless) perc.ag: percent of plant's biomass held aboveground (%) perc.bg: percent of plant's biomass held belowground (%) XN: Percent nitrogen in leaf material (%) X15N: Atom percent 15N in leaf nitrogen used to calculate N fixation (atm%) #### Data File 2: Rhizdiv\_DRYAD\_Nfix data\_6-2024.csv Position: Unique position in the greenhouse (1-1100) Pot: Unique Plant Identifier Species: Legume species. UE = Ulex europaea, SJ = Spartium junceum fert: Fertilization treatment in g/m2/yr N delivered as ammonium nitrate div: Diversity (taxa richness) of rhizobial bacteria used to innoculate the plant (C=no rhizobia Inoculum) bac: The identities of the rhizobia used to inoculate the plants harvest.date: Date the plant was harvested at the end of the experiment stem.biomass: biomass of all aboveground tissue (g) root.biomass: biomass of all belowground tissue (g) nodule.number: number of individual nodules found on the entire root system Rack..: Rack number where the plant's pot was held in the greenhouse.  Observer: Initials of the researcher harvesting the individual plant fert.num: Numeric variable for the fertilization treatments div.num: Numeric variable for the rhizobial diversity treatments tot.biomass: total biomass of the entire plant (g) agbg: aboveground to belowground biomass ratio (unitless) perc.ag: percent of plant's biomass held aboveground (%) perc.bg: percent of plant's biomass held belowground (%) XN: Percent nitrogen in leaf material (%) X15N: Atom percent 15N in leaf nitrogen used to calculate N fixation (atm%) X15Nsoil.mn: Mean of the distribution calculated for the atm % of soil 15N for the plant. Values estimated independently for each fertilization treatment X15Nsoil.sd: Standard deviation of the distribution calculated for the atm % of soil 15N for the plant. Values estimated independently for each fertilization treatment Ndfa: Mean of the calculated value for the percent of the plant's nitrogen derived from fixation activity (%Ndfa). This is the primary estimate of N fixation. Ndfa_sd: Standard Deviation of the distribution for the calculated value for the percent of the plant's nitrogen derived from fixation activity (%Ndfa). Ndfa_LCI: Lower 95% Confidence Interval of the distribution for the calculated value for the percent of the plant's nitrogen derived from fixation activity (%Ndfa). Ndfa_UCI: Upper 95% Confidence Interval of the distribution for the calculated value for the percent of the plant's nitrogen derived from fixation activity (%Ndfa). #### File #3 - Analytical R Code. Rhizobial\_Diversity\_Stats\_and\_Figures\_For\_Submission.R: This file has all statistical and figure creation code presented in the approximate order that is appears in the accompanying manuscript. The code only requires the above-described data files to run (as well as packages loaded internally). ##### Sharing/Access information Please contact Dr. Benton Taylor ([bentontaylor@fas.harvard.edu](mailto:bentontaylor@fas.harvard.edu)) to discuss future publication with these data ## Code/Software One R script file is included that requires both data files to run. Code is annotated and ordered to mirror how the analyses are presented in the corresponding manuscript.