Effects of cerium nitrate on the growth and physiological characteristics in Cyclocarya paliurus seedlings

Field studies were conducted to examine the effects of cerium on the growth and physiological characteristics of Cyclocarya paliurus seedlings by spraying the foliage with different concentrations of cerium nitrate. Optimal concentrations of cerium nitrate improved the relative growth yield of seedling height and stems and the soluble protein and sugar content of the leaves. Cerium nitrate also increased the concentration of secondary metabolites including triterpenoids, quercetin and kaempferol, mineral elements K, P, Mg, Mn, Fe and Cu, and the activities of superoxide dismutase （SOD）, peroxidase （POX）, and phenylalanine ammonia-lyase （PAL） in the leaves. The effects of cerium nitrate on these indices were dose dependent. A concentration of 0.20 mmol/L was optimal to promote the relative growth yield of seedling height, contents of soluble sugar, kaempferol, K, P, Cu, and activities of PAL, SOD, and POX, significantly increased by 54.61%, 14.71%, 55.19%, 105.2%, 74.5%, 133.3%, 80.48%, 25.35% and 22.54%, respectively, as compared with the control. However, the maximal increase in relative growth yield of stems, contents of triterpenoid, quercetin, Mg, Mn, and Fe was attained at 1.00 mmol/L treatment, which significantly increased by 87.00%, 80.56%, 452.44%, 93.2%, 29.4%, and 133.9%, respectively, compared with control check （CK）. Correlation analysis revealed positive relationships between activities of PAL, SOD and contents of triterpenoid, quercetin and kaempferol within a certain concentration range of cerium nitrate. These resuits suggested that an appropriate concentration of cerium not only was effective in the improvement of physiological function of C. paliurus, but also increased seedling resistance. Moreover, it stimulated the synthesis of medicinal components in leaves.