DOI: 10.5061/dryad.rfj6q57n1
title: Data from: The effect of diversity on disease reverses from dilution to amplification in a 22-year biodiversity × N × CO2 experiment

description: Plant disease often increases with N, decreases with CO2, and increases as
 biodiversity is lost (i.e., the dilution effect). Additionally, all these
 factors can indirectly alter disease by changing host biomass and hence
 density-dependent disease transmission. Yet over long periods of time as
 communities undergo compositional changes, these biomass-mediated pathways
 might fade, intensify, or even reverse in direction. Using a field
 experiment that has manipulated N, CO2, and species richness for over 20
 years, we compared the severity of a specialist rust fungus (Puccinia
 andropogonis) on its grass host (Andropogon gerardii) shortly after the
 experiment began (1999) and twenty years later (2019). Between these two
 sampling periods, two decades apart, we found that disease severity
 consistently increased with N and decreased with CO2. However, the
 relationship between diversity and disease reversed from a dilution effect
 in 1999 (more severe disease in monocultures) to an amplification effect
 in 2019 (more severe disease in mixtures). The best explanation for this
 reversal centered on host density (i.e., aboveground biomass), which was
 initially highest in monoculture, but became highest in mixtures two
 decades later. Thus, the diversity-disease pattern reversed, but disease
 consistently increased with host biomass. These results highlight the
 consistency of N and CO2 as drivers of plant disease in the Anthropocene
 and emphasize the critical role of host biomass, despite potentially
 variable effects of diversity, for relationships between biodiversity and
 disease.
description: # Data from: The effect of diversity on disease reverses from dilution to
 amplification in a 22-year biodiversity × N × CO2 experiment Dataset DOI:
 [10.5061/dryad.rfj6q57n1](10.5061/dryad.rfj6q57n1) ## Description of the
 data and file structure Data collected from the long-term BioCON
 experiment at Cedar Creek Ecosystem Reserve, MN, USA. All missing data
 represented as NA. ### Files and variables #### File:
 biocon.fungus.paths.streamline.2.R **Description:** R script to run
 analyses and produce graphs ### File: biocon99-19-allplots.csv
 **Description:** plot-level variables from all plots of the BioCON
 experiment in both 1999 and 2019 ##### Variables * PYID: Plot-Year ID *
 plot: plot number * Year: year of data collection * ring: the experiment
 has a nested design, distributed across 6 'rings' * n: level of
 nitrogen (ambient [AN] or elevated [EN]) * co2: level of CO2 (ambient [AC]
 or elevated [EC]) * nsp: number of species planted in the plot * water: if
 included in the TeRaCON experiment, whether water was manipulated *
 temp: if included in the TeRaCON experiment, whether temperature was
 manipulated * tera: was this plot included in the TeRaCON experiment?  *
 no.tera: was this plot NOT included in TeRaCON, or if it was, were water
 and temperature ambient levels? * fung: percent leaf area of fungal
 damage, averaged among leaves observed in the plot * fungz: standardized
 fung (mean=0, sd=1) * ange.biomass: biomass (g/m2) of the host plant
 Andropogon gerardii in the plot * simp.mass: Inverse Simpson's
 diversity index, calculated from biomass * total.biomass: total plant
 biomass n the plot * other.biomass: biomass of plants other than A.
 gerardii in the plot * mass.legumes: biomass of legumes in the plot *
 nmin: nitrogen mineralization rate (mg N/kg soil/day) * nit: nitrification
 rate * amo: ammonification rate * moist: soil moisture * light: percent
 light penetration * simp.cov: Inverse Simpson's diversity using the
 cover subplot * ange.cov: Percent cover of A. gerardii in the cover
 subplot * real.rich: Realized richness (often a subset of planted
 richness, due to local extinctions) #### File: b.data.tseries.csv
 **Description:** mean biomass of Andropogen gerardii, averaged across
 levels of planted species richness (including both levels of N and CO2)
 ##### Variables * Year: year of the experiment * ange.bm.1: mean biomass
 in monocultures of A. gerardii  * ange.bm.16: mean biomass of A. gerardii
 in plots initially seeded with all 16 species  * ange.biomass.ratio: ratio
 of ange.bm.16 / ange.bm.1 #### File: l.data.tseries.csv 
 **Description:** mean percent light penetration, averaged across levels of
 planted species richness (including both levels of N and CO2) #####
 Variables * Year: year of the experiment * light.1: mean light penetration
 in monocultures of A. gerardii * light.16: mean light penetration in plots
 initially seeded with all 16 species  * light.ratio: ratio of light.16
 / light.1 ## Code/software All analyses were conducted in R.  ## Access
 information Other publicly accessible locations of the data: * email Alex
 Strauss ([atstrauss15@gmail.com](mailto:atstrauss15@gmail.com)) Data was
 derived from the following sources: *
 [https://cedarcreek.umn.edu/research/data](https://cedarcreek.umn.edu/research/data)