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Elevated atmospheric CO2 concentration ([CO2]) can stimulate plant growth through enhanced photosynthetic rate. However, plant C, N and P ratios in response to elevated [CO2] combined with canopy warming in rice-winter wheat rotation system remain largely unknown. Here we investigated the impacts of elevated [CO2] and warming on plant nutrient ratios under open-air conditions. Four treatments including the ambient condition (CK), elevated [CO2] (500 ppm, CE), canopy warming (+2 degrees C, WA), and the combination of elevated [CO2] and warming (CW) were used to investigate the responses of plant C, N and P ratios in a rice-winter wheat rotation system in southeast China. Results showed that elevated [CO2] increased C:N ratio in whole plant by 8.4-14.3% for both crops, and increased C:P ratio by 11.3% for rice. The changes in ratio were due to an increase in C concentration by 0.8-1.2% and a reduction in N concentration by 7.4-10.7% for both crops, and a reduction in P concentration by 10.0% for rice. Warming increased N allocation in rice leaf and N concentration by 12.4% for rice, resulting in increases in the ratios of N to C and P by 11.9% and 9.7% in rice, but not in wheat. However, CW had no effect on plant C:N ratio in rice, indicating the positive effect of elevated [CO2] could offset the negative impact of warming on C:N ratio. By contrast, CW significantly decreased plant C:P and N:P ratios by 16% due to the increase in P allocation in stem for wheat. These results suggest that impacts of climate change on plant nutrient balance occur through interactions between the effects of climate change on nutrient uptake and allocation, which is important for food quality and productivity under global climate change.