Shifts in weed diversity in response to management practices and elevated CO2 in forage bermudagrass (Cynodon dactylon)

Authors: AHLERSMEYER, ANDREW - Auburn University; Prior, Stephen; Runion, George; GAMBLE, AUDREY - Auburn University; MCELROY, SCOTT - Auburn University; RUSSELL, DAVID - Auburn University; Price, Andrew; MAITY, ANIRUDDHA - Auburn University

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2026
Publication Date: 6/10/2026
Citation: Ahlersmeyer, A., Prior, S.A., Runion, G.B., Gamble, A., Mcelroy, S., Russell, D., Price, A.J., Maity, A. 2026. Shifts in weed diversity in response to management practices and elevated CO2 in forage bermudagrass (Cynodon dactylon). Weed Science. 74(1):e43. https://doi.org/10.1017/wsc.2026.10122.
DOI: https://doi.org/10.1017/wsc.2026.10122

Interpretive Summary: Previous work suggests that changes in the environment like rising atmospheric CO2 may affect crop and weed productivity. Plants like a C4 bermudagrass may respond less than C3 crops. This long-term pasture study looked at how both fertility management and elevated CO2 altered growth and weed occurrence. Elevated CO2 did not affect total biomass production, but in unmanaged areas, CO2 showed a greater proportion of weeds, most of which were C3 weeds. Dominance of C3 weeds was generally high, especially in managed plots under elevated CO2. Areas managed with fertilizer and herbicide had a greater proportion of bermudagrass compared to weeds, as well as lower weed densities. Species diversity indices showed higher species richness under elevated CO2, which was exacerbated without proper nutrient and weed management. Findings showed shifts in weed diversity due to changing CO2 levels and the importance of proper crop management.

Technical Abstract: High quality bermudagrass (Cynodon dactylon [L.] Pers.) hay production is a vital component of Southeastern U.S. agriculture. Previous research indicates that environmental change factors like elevated CO2 may significantly affect crop productivity, weed competitiveness, and ecological shifts. Although the effects of rising CO2 on C4 plants like bermudagrass should be marginal, it can affect growth, vigor, and herbicide tolerance in C3 species, which comprise the major weeds in Southeastern U.S. bermudagrass pastures. The objective of this study was to determine the effects of 7 years of management practices and elevated atmospheric CO2 levels on bermudagrass growth, weed competition, and shifts in weed diversity. From 2018 to 2025, bermudagrass was grown in a coarse-textured soil bin at the USDA-ARS National Soil Dynamics Laboratory in Auburn, AL. Open-top chambers delivered either ambient or elevated CO2 (+200ppm), and plots were either managed annually with fertilizer and herbicide or left unmanaged. Elevated CO2 had no significant effect on total biomass production, but in unmanaged plots, CO2 resulted in a significantly greater proportion of weeds. While some C4 grasses and sedges were observed in this experiment, most weed species were C3. Consequently, C3 species dominance was generally high, especially in managed plots exposed to elevated CO2. After 7 years, weeds were identified in all plots, but plots managed with fertilizer and herbicide had a greater proportion of bermudagrass plants to weeds, as well as lower weed densities. Species diversity indices yielded significantly higher species richness under elevated CO2 conditions. Moreover, we observed greater weed diversity with elevated CO2, which was also exacerbated without proper nutrient and weed management. Overall, these findings support previous studies with other plant species that predicted substantial shifts in weed diversity due to environmental change factors like elevated CO2 and the lack of a proper crop management program.