Effects Of Light And Nitrogen On Growth, Photosynthesis And C-N Metabolism Of Fraxinus Mandshurica Seedlings

The matual trees of Ash (Fraxinus mandshurica) are used to the stand site with full lightand fertile soil, and its seedlings have the ability of growthing in understory. Former studiesfound that the amount and developing status of Ash seedlings are better in gaps than innerstands, whether this phenomenon is associated with the increased light and nitrogen (N) or notis ill-defined at present? How the Ash response to the different light intensity and N availabilitydoes is also ambigulous? Therefore, in this study, one-year-old seedlings of Ash were potted insand and treated with two light intensities and combined with four N levels supplied ingreenhouse. We measured the parameters of growth, photosynthesis and carbon-nitrogen (C-N)metabolism, then analyzed the physiological mechanism of seedlings responsing to the abovetreatments, these results may improve the technogy of foresty management and production ofseedlings. The main results were below:Significant decrease in relative growth rate (RGR), net assimilation rate (NAR) and Ncontents in shading treatment compared to full light treatment, by contrast, significant increasein leaf area (LA), shoot/root (S/R), N concentration and N allocation to above ground (stemand leaf). Regardless of light intensity, growth is limited by N deficit, whereas relative growthof root is stimulated by N deficit. Light and N not only significantly influence the seedling'sgrowth, respectively, but also their interactions significantly influence the RGR, NAR andbiomass allocation. These are suggest that one-year-old seedlings of Ash are sensitive to lightand N, and growth in poor environment through changing LA, special leaf area (SLA) and S/R.Net photosynthesis rate (Pn), soluble protein (SP), total N, Chla/b, actual photochemicalefficiency photosystemⅡ(φPSⅡ) and photochemical quenching (qP) are significantlydecreased in shading treatment, but apparent quantum yield (AQY), Fm and chlophyll (Chl)are significantly increased. Pn declining mainly due to N, SP and Chl contents in per unit leafarea are significant decreased. In addition, the parameters between Chl fluorenscence (φPSⅡand qP) and photosynthesis (Pn) are significant correlation (r=0.831, P＜0.05; r=0.818,P＜0.05, respectively), so it can speculate photosynthesis ability by determining Chlfluorenscence.C-N metabolism were significantly influenced by light and N and by the interactionbetween them, making soluble sugar, starch, SP and nitrate reductase (NR) activity weresignificantly decrease. There is a significant negative correlationship between C metabolismand N metaboliam in Ash leaves, suggesting that the ship play an important role in plantgrowth and development. So we should instantly modulate the correlationship in forestymanagement and seedling's culture making the plant in their optical growth rate. In conclusion, the effects of light, N and their interaction on Ash seeling's growth,photosynthesis and C-N metabolism are significant. Shortage of light and N all inhibitseedling's growthing ability, but the seedlings also have the acclimation and adaptation to thedisadvantage environment. It should be noted that our results are derive from the greenhouseand the culture conditions are different to the field, so the results should be tested in the openfield.