Data from: Nitrogen niche partitioning between tropical legumes and grasses conditionally weakens under elevated CO2
Data files
Mar 11, 2024 version files 57.81 KB
Abstract
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.
README: 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)
Methods
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 CO2 (+220 ppm) glasshouse chambers (6 in total, 3 for each CO2 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 Macroptilium bracteatum (Nees. & Marti.) growing with the grass Chloris gayana (Kunth), and the legume Desmodium intortum (Mill) Urb with grass Panicum maximum var. trichoglume (Robyns). The experimental design therefore included the two CO2 treatments (aCO2 and eCO2), 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
Usage notes
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.