Breeding for high maize yields indirectly boosting root carbon in the US Corn Belt since the 1980s

Authors: SCIARRESI, CINTIA - Iowa State University; THIES, AUGUST - Donald Danforth Plant Science Center; TOPP, CHRISTOPHER - Donald Danforth Plant Science Center; EUDY, DOUGLAS - Bayer Crop Sciences, Germany; Kovar, John; TRIFUNOVIC, SLOBODAN - Bayer Crop Sciences, Germany; DIXON, PHILIP - Iowa State University; ARCHONTOULIS, SOTIRIOS - Iowa State University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2025
Publication Date: 2/3/2025
Citation: Sciarresi, C., Thies, A., Topp, C., Eudy, D., Kovar, J.L., Trifunovic, S., Dixon, P.M., Archontoulis, S.V. 2025. Breeding for high maize yields indirectly boosting root carbon in the US Corn Belt since the 1980s. Field Crops Research. https://doi.org/10.1016/j.fcr.2025.109774.
DOI: https://doi.org/10.1016/j.fcr.2025.109774

Interpretive Summary: Crop improvement and evolving management strategies affect root traits. An understanding of root traits is essential for sustainable crop productivity. Our aim with this field study was to quantify historical changes in root traits due to corn breeding and increases in planting density. At seven locations in the Midwest, we measured root mass (weight), root length, specific root length, root: shoot ratio, and root carbon concentration in 11 corn hybrids released from 1983 to 2017 under current (8.7 plants m-2) and historical planting densities (4.7 - 8.7 plants m-2). Root mass increased with the years of hybrid release under both current and historical planting densities, and root mass was significantly correlated with grain yield. However, the gain in root mass due to improved genetics was 9-fold lower than that of grain yield. We also found that newer maize hybrids are adapting to higher planting densities by growing longer roots that are more efficient in capturing nutrients and water. Among the various research locations, the amount of precipitation most affected root growth. In summary, crop improvement has shaped how corn roots grow, emphasizing the role of roots in sustainable agriculture. The increase in root mass suggests more carbon inputs into the soil, thus contributing to overall crop sustainability. These results provide quantitative information on corn root traits and soil carbon inputs to farmers, consultants, agribusiness partners, and state and federal agencies to help guide decisions on sustainability.

Technical Abstract: Understanding changes in below-ground plant traits due to crop improvement is crucial for crop productivity and sustainability assessments. Our objectives were to quantify historical changes in root traits due to maize breeding and plant density increases and assess factors influencing root trait expression under field conditions. We studied root mass, root length, specific root length (SRL), root: shoot ratio, and root carbon concentration in 11 maize hybrids released from 1983 to 2017 under current (8.7 plants m-2) and a historical plant density (4.7 - 8.7 plants m-2). Soil cores were collected from seven US Midwest environments. Root mass linearly increased with the years of hybrid release under both current (0.47% year-1, p = 0.15) and historical (1.27% year-1, p = 0.0028) plant densities. Root mass genetic gain was 9-fold lower than that of grain yield. Root length remained unchanged under current density but increased with historical increases in plant density (0.54% year-1, p = 0.095). Specific root length decreased with the year of hybrid release by -0.53% year-1 (p = 0.0017) in both plant density treatments. The root: shoot ratio did not significantly change with crop improvement (p = 0.26), and there was a trade off between breeding and increasing plant density in this trait. The environment substantially influenced the expression of root traits, with precipitation explaining a portion of the variability. Root mass significantly correlated with grain yield (r = 0.82). Maize breeding and historical increases in plant density synergistically increased root mass, decreased SRL, and maintained the root: shoot ratio unchanged, indicating that crop improvement has altered below-ground maize traits in different directions. The increase in root mass suggests that breeding for high maize yields boosts root carbon inputs and that crop improvement aids sustainability.