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.
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.
Funding provided by: Meat & Livestock Australia
Crossref Funder Registry ID: https://ror.org/02z8j1p10
Award Number: P.PSH. 0793
Funding provided by: Dairy Australia (Australia)
Crossref Funder Registry ID: https://ror.org/02145de51
Award Number: C100002357
Funding provided by: Western Sydney University
Crossref Funder Registry ID: https://ror.org/03t52dk35
Award Number:
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
Files
AGPotData.csv
Additional details
Related works
- Is cited by
- 10.1101/2023.01.16.524162 (DOI)