Responses Of Photosynthetic Characteristics And Nitrogen Metabolism In Torreya Grandis Seedlings To Different Nitrogen Nutrition

Torreya grandis is the multipurpose precious economic tree species, which is timber tree,medicinal tree, fruit tree, tallow tree or ornamental tree, has become the national famous driedfruit products. The seedlings supplied with different nitrogen concentrations (0,4,8,16,32mmol·L-1NH4NO3) and forms (NH+4-N/NO-3-N were0/100,25/75,50/50,25/75and100/0)were studied by hydroponic experiment, and their photosynthetic characteristics and nitrogenmetabolism responses to environmental nitrogen were analyzed. The nitrogen nutrition conditionsto the benefit of seedlings growth and development were also summarized and discussed. Themain results are as follows.(1) The growth index (seedling height increment and ground diameter increment), netPhotosynthetic rate (Pn), stomatal conductance (Gs), PSII actual photochemical efficiency (ΦPSII)Rubisco and photosynthetic nitrogen use efficiency (PNUE) increased with increasing N treatmentuntil reducing at excessively high N supply levels, besides Rubisco all reached the maximum atN8(nitrogen level was8mmol·L-1), and Rubisco reached the maximum at N4(nitrogen level was4mmol·L-1). Higher N supply plants had less leaf nitrogen and invest less N to wall cell (lowerLMA). Compared to N deficiency (N0), significant higher nitrate reductase (NR) activity andNH4+-N content accompanied by lower glutamine synthetase (GS) activity were observed at thehighest N supply (N32). This suggests that the high N concentrations could inhibit the growth ofTorreya grandis seedlings and enzyme activities which related nitrogen metabolism.(2) The nitrogen forms and the ratio had significant impact on the photosynthetic rate, N, P, Kcontent,and the nitrate reductase (NR) activity of Torreya grandis seedlings. With the mixedsupply of NH+-4-N and NO3-N at the ratio of1:1and3:1, the photosynthetic rate, and stomatalconductances (Gs) and transpiration rate (Tr) were significant higher compared to plants fed withsole NH+4-N or NO-3-N. However, there were no different significances in intercellularconcentration (Ci) among different inorganic nitrogen treatments. The sole NH4+-N and NO3--Nfed plants had lower phosphorus (P) and potassium (K) content compared to NH+4-N or NO-3-Nfed plants. Plants supplied with both forms of N (NH4+-N/NO3--N=25/75and50/50) had higherNO-3content and NR activity in comparison to the plants only fed with NO-3-N. Compared to theplants fed with NH+4-N or NO-3-N alone, significant higher N content was observed in the plants fed with NH+4-N in combination with NO-3-N (NH+4-N/NO-3-N=50/50and25/75). We conclude,that Torreya grandis seedlings had no obvious preference to NH4+-N or NO3--N. The mixed supplyof NH+4-N and NO-3-N at the ratio of1:1was able to boost the photosynthesis, nutrientsabsorption and nitrogen metabolism of Torreya grandis seedlings.Above all,8mmol·L-1NH4NO3for nitrogen level and had no obvious preference toNH4+-N or NO3--N. Therefore, the application of the research results could providereasonable nitrogen fertilizer of Torreya grandis seedlings and provide a scientific basisfor nitrogen fertilizer management for grow seedlings of Torreya grandis seedlings andnitrogen fertilizer management of seedlings.