Abstract: We studied the effects of different proportions of inorganic nitrogen(ammonium nitrogen) and organic nitrogen(amino acid nitrogen), accounting for 33% and 67% of total nitrogen, respectively, on plant growth and carbon metabolism of sugar beet in pot experiment. We analyzed the leaf chlorophyll content, total nitrogen and dry matter of leaf and root, the sucrose phosphate synthase(SPS), sucrose synthase(SS), invertase in leaf, the soluble sugar, sucrose and reducing sugar of leaf and root, sugar yield and content at different growth stages of sugar beet. Different nitrogen forms and proportion treatments produced various effects on plant growth and carbon metabolisms at different growth stages of sugar beet. Both above-ground and under-ground dry matter accumulations of sugar beet were increased by different ratios of organic nitrogen treatments. Before harvest, organic nitrogen(67% of total nitrogen application) treatment could promote the growth of sugar beet significantly. However, the amount of dry matter in sugar beet was the highest under organic nitrogen(33% of total N application) treatment in harvest. In the whole growth stage, the leaf chlorophyll content of sugar beet was increased under the organic nitrogen(33% of total nitrogen application) and organic nitrogen(67% of total nitrogen application). After sugar increasing period, the nitrogen accumulations in root and leaf of sugar beet under organic nitrogen treatments were higher than those under inorganic nitrogen treatment, which indicated amino acid nitrogen was a good nitrogen source. Various ratios of organic nitrogen treatments could enhance the SPS, SS and invertase activities in sugar beet leaf at different development stages. With the increase of the proportion of organic nitrogen, soluble sugar and sucrose content were increased significantly in root, the reducing sugar content was declined, and such changes played a functional role in the sucrose accumulation. Sugar content was enhanced with the increase of the organic nitrogen proportion in root. By contrast, both root and sugar yield were the highest when organic nitrogen accounted for 33% of total nitrogen.

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