Data from: Nitrogen niche partitioning between tropical legumes and grasses conditionally weakens under elevated CO2

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.