N₂-fixation is linked to the ability to encroach in African savanna trees

This dataset includes nitrogen (N) dynamics for 12 southern African savanna tree species (six encroachers, six non-encroachers) under manipulated atmospheric CO2 (~398 ppm ambient, ~545 ppm elevated) and soil moisture (well-watered vs water-limited) in open-topped chambers. Measured traits include nodule mass fraction, leaf and stem δ15N, and percentage of N derived from N2-fixation (% Ndfa). The data capture both short- and long-term N allocation strategies and enable exploration of how CO2 and water treatments affect N dynamics across encroaching and non-encroaching species.
, The dataset comprises 12 southern African savanna tree species (nine Vachellia, three Senegalia), with six encroachers and six non-encroachers. All species are facultative N2-fixers. Seeds were obtained from SilverHill Seeds (Cape Town, South Africa), heat-treated at 80 °C for 10 minutes to break dormancy, germinated in November 2021, and transplanted into individual cylindrical pots (20 cm diameter × 75 cm height) containing sieved savanna soil from Fort Beaufort, Eastern Cape, South Africa.
Plants were grown in 16 open-top chambers at Rhodes University Elevated CO2 Facility (Makhanda, South Africa) under ambient (398 ppm) or elevated (545 ppm) CO2~. Soil moisture treatments included well-watered (daily irrigation to ~0.30 volumetric soil moisture) and water-limited (ambient rainfall, ~0.24 SMC). Treatments were fully crossed with approximately five replicates per species per treatment.
Plants were destructively harvested at 11 months. Above- and belowground biomass were separated, ove..., # Data from: N₂-fixation is linked to the ability to encroach in African savanna trees

Dataset DOI: [10.5061/dryad.gqnk98t2f](https://doi.org/10.5061/dryad.gqnk98t2f)

## Description of the data and file structure

The dataset contains measurements of nitrogen (N) dynamics for 12 southern African savanna tree species (six encroachers, six non-encroachers) grown under ambient (\~398 ppm) and elevated (545 ppm) CO~2~, and well-watered or water-limited soil conditions. Recorded traits include nodule mass fraction (NMF), leaf δ^15^N, stem δ^15^N, and percent nitrogen derived from fixation (% Ndfa). The dataset also includes metadata on species identity, encroacher status, CO~2~ and soil moisture treatments, replicate identifiers, and phylogenetic information. Soil δ^15^N measurements are provided for reference. These data allow comparison of short- and long-term N allocation strategies across species and treatments and can be used to explore the role of N2-fixation in plant responses to el...,