Annual dynamics of net ecosystem carbon dioxide exchange in differently managed tallgrass prairies under variable rainfall

Authors: Wagle, Pradeep; Northup, Brian; XIAO, XIANGMING - University Of Oklahoma; KANDEL, TANKA - Former ARS Employee; Cibils, Andres; Gunter, Stacey

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2026
Publication Date: 1/24/2026
Citation: Wagle, P., Northup, B.K., Xiao, X., Kandel, T., Cibils, A.F., Gunter, S.A. 2026. Annual dynamics of net ecosystem carbon dioxide exchange in differently managed tallgrass prairies under variable rainfall. Agricultural and Forest Meteorology. 379. Article 111047. https://doi.org/10.1016/j.agrformet.2026.111047.
DOI: https://doi.org/10.1016/j.agrformet.2026.111047

Interpretive Summary: Although tallgrass prairies across the U.S. Great Plains currently occupy a small portion of their original coverage, these remaining prairies are still key vegetation types and support vital agricultural, ecological, hydrological, and carbon cycling processes. The carbon source-sink status of differently managed tallgrass prairie ecosystems remains largely uncertain because it can be greatly affected by management practices and weather conditions. We used eddy covariance (EC – micrometeorological technique) measurements of carbon dioxide (CO2) fluxes from four co-located native tallgrass prairie pastures to thoroughly evaluate the dynamics of net ecosystem CO2 exchange (NEE) and to examine how variable weather conditions influenced carbon exchange across differently managed native prairies (i.e., prescribed spring burns, intensive and rotational grazing, and haying). Variability in rainfall patterns during the study period (2019-2024) affected biomass production, vegetation dynamics, and carbon exchange patterns differently across management practices. Native prairie ecosystems were net carbon sinks (with NEE sums ranging from -33 to -478 g C m-2) during the growing season (April-October). However, the ecosystems acted as both carbon sources and sinks at the annual scale (annual NEE sums ranging from 104 to -362 g C m-2). Yearly carbon exchange was primarily reflected in the cumulative effects of growing conditions during the season. Our findings emphasize the importance of pasture management, especially intensive practices like prescribed spring burns, heavier grazing, or hay harvesting, to adapt dynamically to variable rainfall patterns and forecasts. Such adaptation is essential to optimize both forage production and carbon sequestration, potentially enabling these systems to outperform less intensive management systems.

Technical Abstract: Tallgrass prairies are vital ecosystems that support regional biodiversity and play a crucial role in global carbon cycling. However, the management practices and disturbances they face can significantly alter their roles as carbon sinks or sources. Despite their importance, the carbon source-sink status of differently managed tallgrass prairies, especially under varying weather conditions, remains uncertain. This study utilized eddy covariance (EC) measurements of carbon dioxide (CO2) fluxes from four co-located southern tallgrass prairie pastures with different management regimes, including prescribed spring burns, intensive and rotational grazing, and haying. The main objectives were to thoroughly evaluate the dynamics of net ecosystem CO2 exchange (NEE) and to examine how diverse weather conditions influenced carbon exchange across differently managed tallgrass prairies. The study period (2019-2024) experienced significant variability in rainfall patterns. Aboveground biomass and satellite-derived vegetation indices displayed distinct year-to-year fluctuations. During the growing season (April-October, DOY ~100-300), these pastures generally behaved as net carbon sinks, with NEE ranging from -33 to -478 g C m-2. However, the magnitude and duration of the carbon sink and the overall annual carbon balance showed considerable interannual variations. Annual NEE ranged from 104 g C m-2 (carbon source) to -362 g C m-2 (carbon sink). Interannual variations in forage production, vegetation dynamics, and NEE were mainly driven by rainfall variability. However, rainfall fluctuations affected carbon exchange patterns differently across management practices. Cross-site analysis revealed a strong correlation (R2 = 0.91) between NEE at annual and seasonal scales, indicating that yearly carbon exchange largely reflects the cumulative effects of growing conditions throughout the season. Our findings highlight the need for adaptive management strategies in intensively managed pastures, specifically tailored to local rainfall patterns and forecasts, to optimize forage production, enhance carbon sequestration, and improve the resilience of grassland ecosystems.