Atmospheric carbon dioxide (CO2) is continuing to rise, creating new questions about how crops, forage grasses, and ecosystems will grow in future climates. Although elevated CO2 often stimulates photosynthesis and biomass production, plants cannot fully convert this extra carbon into growth without enough nutrients, especially nitrogen (N). Perennial grasses such as tall fescue are important for forage, turf, and ecological stability, yet the molecular reasons behind their different responses to CO2 under varying N conditions remain unclear. Against these challenges, deeper investigation is needed into how rising carbon dioxide and nitrogen availability jointly shape hormone metabolism and plant growth.
A research team from the College of Agro-grassland Science, Nanjing Agricultural University, reported these findings (DOI: 10.1093/hr/uhag025) in Horticulture Research on February 2, 2026. The article examined how elevated CO2 affects shoot growth and leaf elongation in tall fescue (Festuca arundinacea) under low nitrogen (LN, 0.25 mM) and moderate nitrogen (MN, 4 mM) conditions. The study was authored by Ningli Fan, Qiuguo Li, Tian Hao, Danyi Wang, Peishuang Yang, Jingjin Yu, and Zhimin Yang.
The team exposed plants to ambient CO2 at 400 μmol mol−1 and elevated CO2 at 800 μmol mol−1, then tracked growth, hormone levels, and key gene-expression patterns. Elevated CO2 increased shoot growth and leaf elongation under both N conditions, but the effect was stronger under MN. Hormone analysis showed that isopentenyl adenosine (iPA), a cytokinin-related compound, increased under both LN and MN, while indole-3-acetic acid (IAA), a major auxin, increased mainly under MN. When plants were treated with lovastatin (LOV), a cytokinin inhibitor, or 2,3,5-triiodobenzoic acid (TIBA), an auxin transport inhibitor, the growth-promoting effect of elevated CO2 was weakened or lost. The researchers further identified two hormone-metabolism genes, FaCKX11 and FaDAO, linked to cytokinin and auxin degradation. In transgenic rice lines overexpressing FaCKX11 or FaDAO, elevated CO2 responses changed sharply: FaCKX11 overexpression blocked growth promotion under LN, while both FaCKX11 and FaDAO altered the response under MN. These effects were associated with cell cycle-related genes OsCycD2 and OsPCNA and the cell elongation gene OsEXPA10.
The authors said the study helps explain why elevated CO2 does not produce a simple “more carbon, more growth” response. Instead, plants appear to route the CO2 signal through different hormone pathways depending on nutrient status. Under nitrogen limitation, cytokinin becomes a major switch for growth, while auxin plays a stronger role when nitrogen supply is more adequate. They said this hormone-based view provides a clearer biological framework for predicting how perennial grasses may respond to future atmospheric conditions.
These findings have practical implications for forage improvement, low-input grassland management, and climate-resilient agriculture. By identifying hormone metabolism as a link between CO2 enrichment and N availability, the study suggests new targets for improving plant productivity when fertilizer input is limited. The results also show that future crop and grass breeding cannot consider carbon fertilization alone; nutrient status and hormone regulation must be evaluated together. Further field-based studies will be needed to test whether these mechanisms hold across environments, soil types, and long-term CO2 exposure, but the work provides a useful molecular entry point for designing plants better adapted to changing climates.
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References
DOI
10.1093/hr/uhag025
Original Source URL
https://doi.org/10.1093/hr/uhag025
Funding information
The study was supported by the National Natural Science Foundation of China (32471773, 32401474).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.