Abstract:The effects of elevated CO2 concentration (550×10-6±50×10-6) on the seed germination and seedling growth of four legume tree species in the lower subtropical forest in Guangdong province were investigated. Higher germination rate (12%) was observed in the elevated CO2 concentration than in ambient CO2 concentration (about 350 × 10-6)for Ormosia glaberrima seeds, but no significant difference was found for other species. Seedlings of the four species produced more root noduls in the elevated CO2 concentration than in ambient CO2 concentration. Nitrogen fixation activities, including TNA and SNA, and content of soluble sugar in root nodule increased in the higher CO2. Net photosynthetic rate of the seedlings of the four species growing in the elevated CO2 environment increased by about 66.7 % ～ 105.9 % ,compared with that growing in ambient CO2. As they were no significant difference in photosynthetic rate was found between the seedlings growing in the high and ambient CO2 concentration measured in the same CO2 concentration (in the high and ambient CO2 concentration respectively). Dark respiratory rate of the leaves of the seedlings growing in the high concentration was not significantly different from that growing in ambient CO2. Total dry matter of the seedling increased in the high CO2 concentration by about 29.79 % ～ 50.30 %. Albizzia lebbeck and Pithecellobium clypearia had significantly higher seedlings in the elevated CO2 concentration than in ambient CO2 concentration, but O. glaberrima and Ormosia pachycarpa had only slightly higher ones. Relative growth rate and unit leaf rate of the seedlings of 30 to 50 days were higher in CO2 enrichment condition, but it was reverse for leaf area ratio. The response to high CO2 concentration was different among the four species. Seedlings of A. lebbeck and P. clypearia showed the most obvious response ,and the two shade-tolerant species, (O. glaberrima and O. pachycarpa) showed the slight response to the elevated CO2 environment.