Altitude-induced variations in hydrothermal conditions and vegetation affect plant nutrients and trade-offs in survival strategies. However, nutrient allocation to different plant organs along altitudinal gradients remains unclear. In the present study, 24 plots were established in the subtropical forests on Daming Mountain, South China, across eight altitudinal gradients (300, 500, 700, 900, 1100, 1200, 1300, and 1400 m). We analyzed the altitudinal patterns and factors influencing carbon (C), nitrogen (N), and phosphorus (P) contents and their ratios in the leaves, branches, and roots of woody plants. We found that branches had higher mean C content and C:N and C:P ratios than roots and leaves, whereas leaves had higher N and P content than roots and branches. The roots exhibited a higher mean N:P ratio than the other organs. An increase in altitude led to a significant rise in leaf and branch C content, aligning with the temperature-plant physiology hypothesis, and a decrease in leaf and branch N content and leaf P, which is consistent with the temperature-biogeochemistry hypothesis. The C:N and C:P ratios in leaves and branches increased with increasing altitude, whereas the N:P ratios in branches and roots decreased significantly. A plant N:P ratio above 16 indicated that P was the primary limiting factor for plant growth in the study area. The positive correlation between N and P contents across plant organs reflects the synergistic absorption of these nutrients by plants. Redundancy analysis revealed that leaf stoichiometric traits were predominantly influenced by soil C:P ratio (SCP), altitude (Alt), soil organic carbon (SOC), slope degree, and soil pH; branch stoichiometric traits were impacted by Alt, SCP, soil water content, SOC, and soil C:N ratio; and root stoichiometric traits were affected by SCP and soil total phosphorus. These findings may elucidate the nutrient allocation patterns and adaptive strategies of plants in subtropical mountains, providing a foundation for forest management and restoration.