Meng et al. (2026) CO2 drove changes in global grassland GPP over the past decade

Identification

• Journal: Ecological Indicators
• Year: 2026
• Date: 2026-01-01
• Authors: Zhe Meng, Yuanyuan Hao, Xuexia Liu, Limin Hua, Yujie Niu
• DOI: 10.1016/j.ecolind.2025.114552

Research Groups

• Key Laboratory of Grassland Ecosystem (Gansu Agricultural University), Ministry of Education, College of Grassland, Gansu Agricultural University, Engineering and Technology Research Center for Alpine Rodent Pest Control of National Forestry and Grassland Administration, Lanzhou 730070, China
• Department of Disturbance Ecology, BayCEER, University of Bayreuth, Bayreuth 95440, Germany

Short Summary

This study investigated global grassland Gross Primary Productivity (GPP) trends and their environmental drivers from 2010 to 2020, finding that GPP increased in 66.44 % of global grassland areas, with atmospheric carbon dioxide (CO2) identified as the dominant contributor, accounting for 44.9 % of the relative impact.

Objective

• To examine global grassland GPP trends and their associations with eight key environmental variables from 2010 to 2020.
• To test the hypotheses that rising atmospheric CO2 is the dominant driver of global grassland GPP, and that the relative importance of environmental drivers varies substantially across climatic zones.

Study Configuration

• Spatial Scale: Global grasslands, delineated by the International Geosphere-Biosphere Programme (IGBP) land cover classification (grasslands, savannas, and woody savannas). Analysis conducted at a 10 km pixel resolution. Regional verification for China's natural grasslands at 1 km resolution.
• Temporal Scale: Main study period: 2010–2020. Supplementary analysis for temporal robustness: 2003–2020.

Methodology and Data

• Models used:
  • Theil-Sen median trend analysis and Mann–Kendall test for trend detection and statistical significance.
  • Ridge regression for spatial sensitivity and contribution analysis, addressing multicollinearity.
  • XGBoost–SHAP assessment for supplementary analysis of nonlinear responses and factor interactions.
• Data sources:
  • Grassland distribution: MODIS MCD12Q1 Version 6.1 land cover product (IGBP classification) via Google Earth Engine (GEE).
  • Gross Primary Productivity (GPP): MODIS MYD17A2H Version 6.1 product (500 m spatial, 8-day temporal resolution, harmonized to 10 km).
  • Environmental variables (all harmonized to 10 km resolution):
    • Fraction of Photosynthetically Active Radiation (FPAR): MOD15A2H v6.1.
    • Atmospheric CO2 concentrations: GOSAT L4B product (~1500 m).
    • Air temperature (Tem): ERA5 reanalysis.
    • Total precipitation (TP): ERA5 reanalysis.
    • Actual evapotranspiration (E): GLEAM.
    • Volumetric soil water layer (VSWL1: 0–7 cm, VSWL2: 7–28 cm): ERA5 reanalysis.
    • Wind speed (WS): ERA5 reanalysis.
  • Validation data: 1 km observation-based Annual GPP (AGPP) dataset for China’s natural grasslands (derived from flux-tower measurements and multi-source satellite data).

Main Results

• Global grassland GPP exhibited an overall increasing tendency from 2010 to 2020, with 66.44 % of areas showing upward trends and 9.19 % showing statistically significant increases (P < 0.05). This pattern was reinforced by the extended 2003–2020 analysis, showing increases in 76.07 % of areas.
• The global multi-year average grassland GPP was 124.39 ± 80.75 g C m⁻². Tropical zones showed the highest productivity (269.46 ± 94.71 g C m⁻²).
• Atmospheric CO2 was the dominant contributor to global grassland GPP variation, accounting for 44.9 % of the total relative impact and an absolute increase of 0.0256 g C m⁻² yr⁻¹. Its influence was most pronounced in tropical regions (56.72 % dominance).
• Fraction of Photosynthetically Active Radiation (FPAR) ranked second (18.94 % globally), with stronger influence in northern temperate grasslands (26.58 %).
• Evapotranspiration (E) contributed more in high-latitude regions, reaching 29.34 % in the northern frigid zone.
• Temperature (Tem) showed relatively stable effects across all climatic zones (6.95 % to 8.51 %).
• Wind speed (WS), total precipitation (TP), and soil moisture (VSWL1, VSWL2) exhibited weaker and more regionally variable influences, with soil moisture showing limited global contributions (0.94 %–3.76 %).
• Supplementary analyses (2003–2020 extended period and XGBoost–SHAP model) consistently validated the dominant role of atmospheric CO2 and the spatial patterns of other drivers.

Contributions

• Systematically revealed the global spatiotemporal trends of grassland GPP and eight associated environmental drivers using robust trend analysis methods.
• Quantified the spatial contributions of multiple environmental variables to grassland GPP using ridge regression, identifying their relative influence and regional heterogeneity, thereby providing empirical evidence for the dominant role of CO2 and the variation in driver importance across climatic zones.
• Enhanced the robustness of findings through complementary validations, including an extended temporal analysis (2003–2020) and an XGBoost–SHAP assessment to capture nonlinear responses and interactions.
• Highlighted the pronounced global spatial heterogeneity in environmental controls on grassland productivity, emphasizing the necessity of integrative frameworks for future assessments.

Funding

• Merit-based Innovation Program of Key Laboratory of Grassland Ecosystem of Ministry of Education (Project No. KLGE-2024-06)
• Young Graduate Student Supervisor Support Fund of Gansu Agricultural University (Project No. GAU-QDFC-2025-06)
• National Key Research and Development Program Project of China (Project No. 2024YFD1400502)

Citation

@article{Meng2026CO2,
  author = {Meng, Zhe and Hao, Yuanyuan and Liu, Xuexia and Hua, Limin and Niu, Yujie},
  title = {CO2 drove changes in global grassland GPP over the past decade},
  journal = {Ecological Indicators},
  year = {2026},
  doi = {10.1016/j.ecolind.2025.114552},
  url = {https://doi.org/10.1016/j.ecolind.2025.114552}
}