Abstract:

Light and nitrogen (N) are two main environmental factors affecting plant growth and physiological process. With sand culture in greenhouse, the growth and carbon-nitrogen metabolism of one-year-old Fraxinus mandshurica (Ash) seedlings were analyzed under two light intensities and four N concentrations. The results showed that compared with full light, shading increased the specific leaf area, crown to root ratio (C/R), whole plant leaf area and leaf mass ratio by 35.5%, 24.9%, 21.8% and 18.5%, respectively, but whole plant biomass decreased 19.6%. Under two light intensities, whole plant biomass and leaf area increased significantly with increasing N supply (P<0.05). Furthermore, soluble sugar content, starch content and total non-structural carbon (TNC) content decreased significantly under shading treatment, and starch content and total non-structural carbon content also decreased with increasing N supply (P<0.05). In addition, shading decreased the nitrate content and nitrate reductase (NR) activity in leaves, but the soluble protein content significantly increased (P<0.05). At two light intensities, soluble protein content and NR activity increased, while nitrate content decreased with increasing N supply. There was a significant positive correlation between soluble sugar content and nitrate content (r=0.944, P<0.01), while other carbon metabolism (soluble sugar content, starch content and TNC content) and N metabolism (soluble protein content, nitrate content and NR activity) tend to be a negative correlation, but not significant. In conclusion, one-year-old Ash seedlings were very sensitive to light and N. Low light intensity and N deficiency finally lead to poor growth of Ash seedlings, although the seedlings had somewhat ability for adapting the low light and N deficiency.

Key words: Fraxinus mandshurica, light intensity, shading, nitrogen, C-N metabolism