Abstract: Aims Elevated atmospheric ozone (O₃) concentrations significantly affect plant nutrient allocation, thereby regulating litter decomposition. However, the stoichiometric responses of leaf and fine root litters to O₃ stress remain unclear. This study aimed to investigate how elevated O₃ influences the dynamics and regulatory mechanisms of carbon (C), nitrogen (N), and phosphorus (P) stoichiometry during the decomposition of leaf and fine root litter. Methods A 12-month decomposition experiment was conducted using Koelreuteria paniculata and Camellia sinensis at the O₃-FACE platform in Yanqing, Beijing. Two O₃ treatments were applied: ambient air (NF) and elevated O₃ (NF60, ambient air + 60 ppb O₃). At four decomposition stages (T0, T1, T3, and T12), we measured litter C, N, and P concentrations and stoichiometric ratios (C/N, C/P, N/P). Important findings Elevated O₃ significantly altered the initial stoichiometric structure and residual characteristics of the litter. Under NF60, the initial C/N ratio of K. paniculata leaves increased by 7.6%, while N/P decreased by 17.7%, leading to a 10.3% increase in residue mass after 12 months. For C. sinensis fine roots, P concentration increased by 11.1% and C/P decreased by 14.5%, indicating enhanced P redistribution. Litter residue was significantly correlated with C/N, C/P, and N/P ratios (P < 0.05). During decomposition, the N/P ratio in K. paniculata and C. sinensis leaves increased by 43.6%–68.0% and 52.9%–59.3%, respectively, suggesting strengthened phosphorus limitation in later stages, consistent with the “Growth Rate Hypothesis” and the “N:P Threshold Hypothesis.” Elevated O₃ induces a “high-C/low-P” stoichiometric pattern, exacerbating microbial nutrient limitation and slowing carbon mineralization. Leaves and fine roots exhibit contrasting responses: K. paniculata leaves are more constrained by P availability, while C. sinensis fine roots maintain higher decomposition efficiency through enhanced P redistribution. These findings highlight organ-specific adaptive strategies to O₃ stress and provide novel insights into stoichiometric regulation of litter decomposition under global change.

Key words: Ecological stoichiometry, Litter decomposition, Ozone stress, C/N/P, Leaves and fine roots