Nitrogen addition drives local extinction of legumes in meadow steppe
Data files
Jun 05, 2025 version files 751.66 KB
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data_legume_diversity.xlsx
748.83 KB
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README.md
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Abstract
Nitrogen (N) enrichment poses a critical threat to legume diversity through three interlinked mechanisms: stimulating growth of non-leguminous competitors, enhancing community canopy coverage, and inducing light limitation. Canopy management practices such as mowing may partially mitigate these impacts by reducing species dominance and restoring light availability.
Through a decadal field experiment in a meadow steppe, we systematically investigated the interactive effects of chronic N addition and mowing regimes on legume biomass dynamics and species persistence.
Our findings demonstrate a time-dependent relationship between N enrichment and legume species richness. Most legume species, particularly rare and subordinate ones, were eliminated at intermediate-to-late stages when N addition rates exceeded 10 g N m−2 yr−1. This collapse correlated with the progressive suppression of legumes by biomass accumulation in the dominant non-legume species, Leymus chinensis. Beyond this ecological threshold, only Thermopsis lanceolata persisted in the community, though its biomass ultimately declined with increasing N inputs and associated metal element uptake. Greenhouse experiments revealed this species' survival strategy involves rapid downregulation of N fixation capacity − a potentially critical functional trait distinguishing it from other legumes in the study site. Mowing partially counteracted N induced biodiversity loss at sub-threshold enrichment levels (i.e., ˂ 10 g N m−2 yr−1) by weakening the competitive dominance of nitrophilous plants and maintaining light penetration. However, this management intervention proved ineffective against legume extirpation under prolonged N exposure or supra-threshold addition rates. Our mechanistic analysis identified three cascading drivers of legume extinction: (1) competitive exclusion by N-responsive species, (2) light limitation from canopy closure, and (3) phytotoxic effects of metal element accumulation.
Synthesis. This study predicts an ecosystem regime shift toward simplified N₂-fixing associations and dominance of non-symbiotic plant species in temperate grasslands under chronic N deposition. Such compositional changes could fundamentally alter terrestrial N cycling patterns, with cascading consequences for ecosystem functioning. While mowing provides limited buffering capacity at moderate N loads, our results emphasize the imperative for stricter atmospheric N emission controls to preserve legume biodiversity and associated ecological services.
Description of the data and file structure
The dataset is related to the paper "Nitrogen Addition Drives Local Extinction of Legumes in Meadow Steppe". The excel file contains four sheets. The “field experiment” (contains data from 2014-2023), “light transmittance” (2023) and “soil data” (2023) sheets contain data collected from the study site (field), and “greenhouse” sheet contains data collected in 2019 from the greenhouse of Thermopsis lanceolata.
Description:
Variables
- plot: The nitrogen (N) treatment plot. The study site contains 480 plots, of which 384 are relevant to our study.
- block: Study block. Each block contains 60 plots and total 8 blocks.
- type: N fertilizer types. This study includes (NH₄)₂SO₄, NH₄HCO₃, urea, slow-release urea.
- dose: the N addition rates. Six rates are included, which are 0, 2, 5,10, 20 and 50 g N m⁻² yr⁻¹.
- mowing: The mowing treatment.
- year: The study year.
- ANPP: Aboveground net primary productivity in each plot (g m⁻² yr⁻¹).
- legume biomass: The aboveground biomass of the legume functional groups in each plot (g m⁻² yr⁻¹).
- abundance: The legume richness in each plot, which refers to the total number of legume species.
- T.l biomass: The aboveground biomass of the dominant legume, Thermopsis lanceolata, in each plot (g m⁻² yr⁻¹).
- L.c biomass: The aboveground biomass of the dominant grass, Leymus chinensis, in each plot (g m⁻² yr⁻¹).
- relative biomass of L.c: The relative biomass of Leymus chinensis, which is ratio of L.c biomass to ANPP.
- relative biomass of legumes: The relative biomass of the legume group, which is referred to the ratio of legume biomass to ANPP.
- relative biomass of T.l: The relative biomass of Thermopsis lanceolata, and is calculated as its biomass divided by ANPP.
- relative biomass of T.l in legumes: The percentage of Thermopsis lanceolata in the legume group, which is the ratio of Thermopsis lanceolata biomass to legume biomass.
- precipitation: The precipitation (mm) in the growing season (from June to August). NA means not available data.
- AGB: The aboveground biomass ( g plant⁻¹).
- BGB: The belowground biomass ( g plant⁻¹).
- total biomass: The sum of AGB and BGB ( g plant⁻¹).
- nodule biomass: The biomass of nodules in each plant ( mg nodule g plant⁻¹).
- investment: The investment to nodulation, which is based on the nodule biomass divided by the total biomass.
- Ramet: The ramet number of each plant.
- light0%: The light transmittance at the litter layer.
- light20%: The light transmittance at 20 cm above the litter layer.
- element: Measured metal element in plants and soil, which includes Fe, Mn, Al and Ca.
- content: The content of each element ( mg kg⁻¹).
- species: The studied items.