In forage grasses,the nitrogen concentration is directly related to the nutritional value.The studies examined the hypothesis that global elevation of CO2 concentration probably affects the biomass,nitrogen(N) concentration,and allocation and distribution patterns in the organs of forage grasses.While sainfoin(Onobrychis viciaefolia Scop.) seedlings grew on a low nutrient soil in closed chambers for 90 days,they were exposed to two CO2 concentrations(ambient or ambient + 350 μmol mol-1 CO2) without adding nutrients to them.After 90 days exposure to CO2,the biomasses of leaves,stems,and roots,and N concentrations and contents of different parts were measured.Compared with the ambient CO2 concentration,the elevated CO2 concentration increased the total dry matter by 25.07%,mainly due to the root and leaf having positive response to the elevated CO2 concentration.However,the elevated CO2 concentration did not change the proportions of the dry matters in different parts and the total plants compared with the ambient CO2 concentration.The elevated CO2 concentration lowered the N concentrations of the plant parts.Because the dry matter was higher,the elevated CO2 concentration had no effect on the N content in the plants compared to the ambient CO2 concentration.The elevated CO2 concentration promoted N allocations of the different parts significantly and increased N allocation of the underground part.The results have confirmed the previous suggestions that the elevated CO2 concentration stimulates plant biomass production and decreases the N concentrations of the plant parts. In forage grasses, the nitrogen concentration is directly related to the nutritional value. These studies examined the hypothesis that global elevation of CO2 concentration probably affects the biomass, nitrogen (N) concentration, and allocation and distribution patterns in the organs of forage grasses. While sainfoin (Onobrychis viciaefolia Scop.) seedlings grew on a low nutrient soil in closed chambers for 90 days, they were exposed to two CO2 concentrations (ambient or ambient + 350 μmol mol-1 CO2) without adding nutrients to them. After 90 days exposure to CO2, the biomasses of leaves, stems, and roots, and N concentrations and contents of different parts were measured. Compared with the ambient CO2 concentration, the elevated CO2 concentration increased the total dry matter by 25.07%, mainly due to the root and leaf has positive response to the elevated CO2 concentration. However, the elevated CO2 concentration did not change the proportions of the dry matters in different parts and the total plan ts compared with the ambient CO2 concentration. The elevated CO 2 concentration. The elevated CO 2 concentration had no effect on the N content in the plants compared to the ambient CO 2 concentration. elevated CO2 concentration promoted N allocations of the different parts significantly and increased N allocation of the underground part.The results have confirmed the previous ago that the elevated CO2 concentration stimulates plant biomass production and decreases the N concentrations of the plant parts.