DOI: 10.5061/dryad.nk98sf7ww
title: Data from: Nitrogen niche partitioning between tropical legumes and grasses conditionally weakens under elevated CO2

description: Plant community biodiversity can be maintained, at least partially, by
 shifts in species interactions between facilitation and competition for
 resources as environmental conditions change. These interactions also
 drive ecosystem functioning, including productivity, and can promote
 over-yielding- an ecosystem service prioritized in agro-ecosystems, such
 as pastures, that occurs when multiple species together are more
 productive than the component species alone. Importantly, species
 interactions that can result in over-yielding may shift in response to
 rising CO2 concentrations and changes in resource availability, and the
 consequences these shifts have on production is uncertain especially in
 the context of tropical mixed-species grasslands. We examined the relative
 performance of two species pairs of tropical pasture grasses and legumes
 growing in monoculture and mixtures in a glasshouse experiment
 manipulating CO2. We investigated how over-yielding can arise from
 nitrogen (N) niche partitioning and biotic facilitation using stable
 isotopes to differentiate soil N from biological N fixation (BNF) within N
 acquisition into aboveground biomass for these two-species mixtures. We
 found that N niche partitioning in species-level use of soil N vs. BNF
 drove species interactions in mixtures. Importantly partitioning and
 overyielding were generally reduced under elevated CO2. However, this
 finding was mixture-dependent based on biomass of dominant species in
 mixtures and the strength of selection effects for the dominant species.
 This study demonstrates that rising atmospheric CO2 may alter niche
 partitioning between co-occurring species, with negative implications for
 the over-yielding benefits predicted for legume-grass mixtures in working
 landscapes with tropical species. Furthermore, these changes in
 inter-species interactions may have consequences for grassland composition
 that are not yet considered in larger-scale projections for impacts of
 climate change and species distributions.  
description: These data were collected as part of a glasshouse experiment run
 at the Hawkesbury Institute for the Environment at Western Sydney
 University lead by A. Churchill (the first author). Detailed methods
 associated with the experimental design may be found in the linked
 manuscript and eventual published paper, however in brief:
 Plants were grown in ambient and elevated
 CO<sub>2</sub> (+220 ppm) glasshouse chambers (6 in total, 3
 for each CO<sub>2</sub> treatment). Plants were grown either
 in monoculture (2 individuals each) or in mixture (1 individual of two
 species; a legume and a grass) for two pairs of grass-legumes. All plant
 species are common tropical forages, frequently grown together in field
 condiitons in Eastern Australia and elsewhere around the globe. Specific
 species include <em>Macroptilium bracteatum</em> (Nees.
 & Marti.) growing with the grass <em>Chloris
 gayana</em> (Kunth), and the legume <em>Desmodium
 intortum</em> (Mill) Urb with grass <em>Panicum maximum var.
 trichoglume</em> (Robyns). The experimental design therefore
 included the two CO<sub>2</sub> treatments (aCO2 and
 eCO<sub>2</sub>), six types of plant combinations in pots
 (grass1, legume1, mixed1, grass2, legume2, mixed2), and twelve replicates
 per plant combination per treatment (four replicates per
 chamber). All plant seeds associated with this
 experiment were coated with AgriCote advanced seed coating, and legumes
 came pre-inoculated with appropriate rhizobia. Seeds were geminated in
 seedling trays, and re-potted into pots after three weeks of growth. Pots
 used for the duration of the experiment were 3.7L volume, filled with 3.9
 kg of soil that included field soil from the Hawkesbury Forest Experiment
 (sieved to 5mm) and quartz sand ( 7:3 v/v). All plants were grown for 11
 weeks in individual glasshouse chambers prior to harvest. Aboveground
 plant tissue was clipped at the soil surface, dried, homogenized and
 analyzed for C, N (including 15N) and P following standard practices (see
 publication for details). All belowground biomass was retained using 2mm
 sieves with water prior to drying. We quantified legume nodule number,
 density and mass for all legume and mixed species pots, as well as using
 acetylene reduction assays to estimate a proxy for instantaneous rates of
 nitrogenase activity of bactieria in nodules. Soil nutrients were
 quantified using ion exchange resins extracted with 0.5 M HCl to determine
 NO3-, NH4+, and PO4-3.  We calculated the contribution
 of biological nitrogen fixation using 15N concentrations (details
 described in main text) as well as calculating the potential overyield and
 net biodiversity effect of increased production in mixed pots relative to
 the mass of grass and legumes grown in monoculture. Net Biodiversity
 Effect was partitioned into Complementarity Effect and Selection Effect
 respectively based on chamber level averages, and those calculated values
 are also included here. There are three datasets
 included with this paper: AGPotData- includes all data
 associated with plant shoots/ aboveground components
 BGPotData- includes all data associated with plant roots/
 belowground components Churchill_NEBpartitioned-
 includes Net Biodiversity Effect, Complementarity Effect, and Selection
 Effect using chamber averages for each monoculture species 
description: All files included here are .csv files that can be opened with
 any standard spreadsheet reader. Original data analysis was conducted
 using R, and scripts associated with this analysis may be accessed through
 the corresponding author.
description: # Data for: Nutrient niche partitioning between tropical legumes and
 grasses conditionally weakens under elevated CO2 These data were collected
 as part of a glasshouse experiment run at the Hawkesbury Institute for the
 Environment at Western Sydney University lead by A. Churchill (the first
 author). Detailed methods associated with the experimental design may be
 found in the linked manuscript and eventual published paper and in the
 associated 'Methods' description on Dryad Details for the types
 of data included in each file, as well as explanations for abbreviations
 and units are included in this file for use by others ## Dataset:
 AGPotData This dataset includes all data collected from plant shoots as
 part of the experiment described in associated publications. Columns
 represent multiple types of measurements on the same plant, where each row
 is a unique plant that can be linked by the pot number (PotNum) to data in
 other datasets (note that these are aggregated to all plants within a pot
 due to the nature of how measurements were collected) Column headers
 (Title, explanation, units) PotNum: Pot number, includes chamber (1-6) and
 then within chamber unique identifier (note that these are not all
 sequential due to parallel experiment not included here) PotLabel: Unique
 identifer that summarizes all treatment information, including
 'e' vs 'a' CO2 conditions, any nutrients added (all
 values here will be '0', single letter designation for species-
 B,D,R,P- and whether plants were allowed to regrow after clipped- all
 values here will be 'N') Chamber: Ordinal 1-6 CO2: Category- two
 treatment levels- Ambient (410-430 ppm) and Elevated (630-650 ppm)
 SpeciesPair: Category- either BurRho (Burgundy Bean and Rhodes grass,
 referred to as MacChl in publications) or DesPan (Desmodium and Panic
 grass, referred to as DesPan in publications) PotType: Category containing
 information on the specific species or species combination in pot
 (Burgundy, BurRho, Rhodes, Desmodium, DesPan, Panic) Species- Common name
 of species associated with specific row (individual plants within pot)
 including- Burgundy, Rhodes, Desmodium, and Panic PlantType: Category
 describing plant functional group of species in row (Legume, Grass) and
 for mixed pots whether the individual was grown with a legume (L-Grass) or
 with a grass (G-Legume) FunxnlGroup: Category describing plant species
 functional group for individual plants within a pot (Grass or Legume)
 Sward: Category describing the mixture type for individuals within the
 pot- including Grass, Legume, or Mixed SwardType: Category describing each
 pot and species as either monoculture (Mono) or Mixed NumPlant: The number
 of species within a pot (either 1 or 2) PlantID: Number used to track
 repeated measurements on the two individual plants within a pot Replicate:
 Replicate number within a chamber for specific treatment and species
 combinations DW: Dry weight after drying to constant mass in an oven (g)
 P_ppm: Concentration of Phosphorus in shoot plant tissue (ppm) C_Per:
 Concentration of Carbon in shoot plant tissue (%) Delta15N: Concentration
 of 15N-Nitrogen in shoot plant tissue (per mil) N_Per: Concentration of
 Nitrogen in shoot plant tissue (%) Fix_Prop: Percent of shoot Nitrogen
 derived from biological nitrogen fixation (%) ## BGPotData Column headers
 (Title, explanation, units) PotNum: Pot number, includes chamber (1-6) and
 then within chamber unique identifier (note that these are not all
 sequential due to parallel experiment not included here) PotLabel: Unique
 identifer that summarizes all treatment information, including
 'e' vs 'a' CO2 conditions, any nutrients added (all
 values here will be '0', single letter designation for species-
 B,D,R,P- and whether plants were allowed to regrow after clipped- all
 values here will be 'N') Chamber: Ordinal 1-6 CO2: Category with
 two treatment levels- Ambient (410-430 ppm) and Elevated (630-650 ppm)
 SpeciesPair: Category- either BurRho (Burgundy Bean and Rhodes grass,
 referred to as MacChl in publications) or DesPan (Desmodium and Panic
 grass, referred to as DesPan in publications) PotType: Category containing
 information on the specific species or species combination in pot
 (Burgundy, BurRho, Rhodes, Desmodium, DesPan, Panic) Sward: Category
 describing the mixture type for individuals within the pot- including
 Grass, Legume, or Mixed Replicate: Replicate number within a chamber for
 specific treatment and species combinations Plant1_NumNodules: Number of
 nodules in root system based on subset mass (count of nodules) TotalDW:
 Pot level total belowground biomass (g) NumLegPlants: Number of legume
 individual plants in a pot (0, 1, or 2) Nodule_Act_Cal: Rate of acetylene
 reduction to estimate biological nitrogen fixation (micro mols per g of
 nodules) PO4: Concentration of PO4-3 from resin extraction (0.5M HCl; mg
 kg-1) NO3: Concentration of NO3- from resin extraction (0.5M HCl; mg kg-1)
 NH4: Concentration of NH4+ from resin extraction (0.5M HCl; mg kg-1) ##
 Churchill\_NBEpartitioned Column headers (Title, explanation, units)
 PotNum: Pot number, includes chamber (1-6) and then within chamber unique
 identifer (note that these are not all sequential due to parallel
 experiment not included here) CO2: Two treatment levels- Ambient (410-430
 ppm) and Elevated (630-650 ppm) SpeciesPair: Category- either BurRho
 (Burgundy Bean and Rhodes grass, referred to as MacChl in publications) or
 DesPan (Desmodium and Panic grass, referred to as DesPan in publications)
 SpeciesPair: Category- either BurRho (Burgundy Bean and Rhodes grass,
 referred to as MacChl in publications) or DesPan (Desmodium and Panic
 grass, referred to as DesPan in publications) Yo: Estimated total summed
 shoot biomass based on chamber mean values for monoculture species (g)
 NBE: Net Biodiversity Effect (g) CE: Complementarity Effect (g) SE:
 Selection Effect (g)