Growth Response Of Major Tree Species Seedlings In Phyllostachys Edulis-Broadleaf Mixed Forest To Nitrogen Nutrition

Nitrogen,the nutrient elements of highest demand for plant growths,is the important components to synthesize proteins,nucleic acids,enzymes and secondary metabolites in plant tissues,and also the common limiting factor during the growth and development of plants.NH₄⁺-N and N0₃^--N in soils are the primary inorganic nitrogen forms that plants can use.In the long term evolution,plants have evolved the preference to nitrogen forms in soils due to the greatest differentiation of environmental condition,plant species and nutritional characteristics of nitrogen original.We,adopting the method of watering nutrient solution to potted plants in indoor,explored the growth of five plants including Phyllostachys heterocycla,Castanopsis fargesii),Machilus pauhoi,Sapium discolor and Camellia Oleifera at different nitrogen levels of 2 mmol·L^-1(0.4 mmol·L^-1 N₁,N₂ and N₃ 8mmol·L^-1)and nitrogen forms(NH₄⁺-N,NO₃^--N,respectively 4:0（NH₄）,1:1（NH₄⁺NO₃）,0:4（NO₃）.The object of this study was to clarity the preference of these plant species to the nitrogen levels and forms in soils.The results are as followed.1.Phyllostachys heterocycla is a plant species preferting to ammonium.The height,leaf number,leaf area,chlorophyll SPAD value,dry matter accumulation and root morphology of its seedling were significantly affected by the nitrogen levels and forms.The results showed that,all growth indexes of P.heterocycla were maximal at N₃ levels with 8 mmol·L^-1 of NH₄⁺-N,while these were minimal at N₁ levels with 0.4 mmol·L^-1 of NO₃^--N.It indicated that NH₄⁺-N had a better function to promote the growth of P.heterocycla compared with NO₃^--N.Moreover,the efficiency was increased with the increase of total nitrogen.In contrast,the growth of P.heterocycla was restrained when using NO₃^--N as the nutrient solution.2.Castanopsis fargesii is a neutral tree species,but a little ammonium preferences.The results,from the study to the effects of different nitrogen levels and forms on this plant species,showed that the growth of C.fargesii attained to the highest values on the height,leaf number,leaf area,chlorophyll SPAD value,dry matter accumulation and root morphology at N₃ level when the ratio between NH₄⁺-N and NO₃^--N was 1:1,which indicated that this ratio was suitable to the growth of C.fargesii,then the ratio between them was 4:0.It indicated that NH₄⁺might be favorable for the growth of C.fargesii seedings,while excessive NO₃^-was unfavorable for them at a suitable Nitrigen level.3.Machilus pauhoi is neutral species,and mixed culture conditions were favorable for the growth and development of M.pauhoi seedling.Through the study of different nitrogen concentration and nitrogen form,we showed that the height,leaf number,leaf area,chlorophyll SPAD value,dry matter accumulation and root morphology of M.pauhoi was maximal in N₃ level with the ratio of 1:1 between NH₄⁺-N and NO₃^--N,which indicated that the concentration were suitable for the growth and development of this species.But all these growth indexes did not vary significantly between NH₄⁺-N and NO₃^--N levels.4.Sapium discolor is a neutral species for nitrogen forms,and it was very favotable for the growth and development of seedings at mixed culture conditions.The seedings had the high values of height,leaf number,leaf area,chlorophyll SPAD value,dry matter accumulation and root morphology at N₃ level(nitrogen concentration of 8 mmol·L^-1)with the ratio of 1:1 between NH₄⁺-N and NO₃^--N,and followed at N₃ level the ratio of 4:0between them.These results indicated it was also favorable for the growth of this species at suitable nitrogen levels.5.Camellia Oleifera prefers ammonium in soils.The results showed that the use of NH₄⁺-N increased the growth ofC.Oleifera seedlings.The height,leaf number,leaf area,chlorophyll SPAD value,dry matter accumulation and root morphology of its seedling would increase with the concentrate of NH₄⁺-N,and gained the maximum at N₃ levels.In contrast,these indexes,in particular the quality of roots,were affected under the use of NO₃^--N,and arrived at the minimal values at N₁ levels with 0.4 mmol·L^-1 of NO₃^--N.The results showed that five plant species in Phyllostachys edulis-broadleaf mixed forest had different response to the change of nitrogen supply.The expansion of P.heterocycla might improve the content of NH₄⁺-N in Soils,which was profitable to some species preferring NH₄⁺forms,while P.heterocycla compared with them had has a faster growth and fecund.Therefore,the change of nitrogen in soils that caused by P.heterocycla expanding to broadleaved evergreen forest is probably nitrogen nutrient strategy in soil of its expansion.