Abstract: To explore the regulatory effect of different light intensity and nitrogen level on carbon-nitrogen metabolism in young and old bamboo leaves, and to seek suitable light and nitrogen conditions for the growth of Dendrocalamopsis oldhami, bamboo culms cultivated in solar greenhouse were treated under conditions of a permutation of two light intensity levels (Ls for strong and Ln for weak) and three nitrogen levels (N0 for no nitrogen, N1 for low nitrogen and N2 for high nitrogen). The results showed that, when nitrogen fertilizer was not applied, the content of chlorophyll and the ABS/CSo, φPo of young leaves under Ls treatment were significantly lower than that of Ln, the activity of enzymes related to carbonnitrogen metabolism, organic carbon and total nitrogen content were significantly higher than that of Ln, and with no difference in PI_ABS and C/N. Under Ln and Ls treatments with nitrogen supply, the maximum chlorophyll content of young leaves was found with N1/N2 and N2, the maximum ABS/CSo occurred with N0, the maximum φPo orPI_ABS occurred with N2 and N2, the maximum GS, NR, AMY, SS occurred with N2 and N2, the maximum organic carbon occurred with N1/N2 and N1, the maximum total nitrogen occurred with N1/N2 and N2, and the maximum C/N occurred with N0 and N0/N1, respectively. In addition, the responses of chlorophyll fluorescence parameters and the activities of enzymes related to carbonnitrogen metabolism to different nitrogen fertilization levels were lower than that to different light intensities, especially for old leaves. Compared with young leaves, PI_ABS of old leaves were lower under Ls than under Ln. The interactive effects of light intensity and nitrogen supply on the enzyme activities of NR and SS of old leaves were not significant, with C/N of old leaves reaching the minimum value under the condition of no nitrogen supply. Our results suggest that light intensity was the dominant factor affecting carbon-nitrogen metabolism of D. oldhami leaves. The southward D. oldhami can inhibit its leaf function due to strong light intensity. In the short term, the overall leaf function can be protected by its own defense system. Because of the weak light on the north row, the growth rate and the ability to absorb nitrogen were low, and the leaf sensitivity to nitrogen was poor. Nitrogen addition increased carbon-nitrogen metabolic activity, but they were not proportional. Young leaves were more sensitive to nitrogen supply than old leaves. High nitrogen level (N2) increased the carbon-nitrogen metabolism of D. oldhami leaves, including chlorophyll content, activity of enzymes related to carbonnitrogen metabolism, total nitrogen accumulation, and thus accelerated growth rate.

Key words: light intensity, nitrogen fertilization, interaction effect, chlorophyll, fluorescence parameter, enzyme related to carbon-nitrogen metabolism, ratio of carbon to nitrogen (C/N).