Response Of Photosynthesis And Nitrogen Metabolism In Populus Simonii×P.nigra Seedlings To Nitrogen Forms And Nitrogen Supply

Nitrogen(N)is one of the most important mineral elements for plants.Poplar,which is one of important greening and economic forest trees,could be limited seriously by nitrogen to the growth and development process.Therefore,effects of nitrogen forms and supply on growth and biomass in poplar plants could be investigated to improve poplar's yield and quality,and enrich the theory of poplar plantation.In this paper,using Populus simonii X P.nigra grown in pots as test materials,the test treatments were taken as five levels of nitrogen supply,0.1,0.5,1.0,5.0 and 10 mmol/L respectively(NH4Cl and NaNO3 as the nitrogen source),respectively,a total of 10 group treatment.The photosynthetic parameters in leaves of test plants were investigated during 4 weeks treatment,and then,test plants were harvested.At same time,morphological and physiological indicators in roots,stems,leaves related to nitrogen metabolism were investigated to analyze effects of nitrogen forms and supply on the growth and development in black poplar seedlings.The main results were as follows:(1)Under different nitrogen form and concentration,Populus simonii × P.nigra has a different reaction in nitrogen metabolism.Nitrate reductase(NR)activities in roots and leaves increased with nitrogen concentration,but glutamine synthetase(GS)activities in roots,stems and leaves decreased with nitrogen under lower concentration ammonium treatment PopulusRoot GS activity highest in 5 mmol/L level.The activity of Glutamate synthase(GOGAT)in Populus seedlings roots,stems and leaves are not the same.Under ammonium treatment,root glutamate synthetase activity reached the highest in 5 mmol/L treatment,while the leaf activity in 10 mmol/L reached the highest activity,changes in stem irregular activity in nitrate treatment.Under nitrate treatment of 5 mmol/L and 1mmol/L glutamate synthases(GOGAT)activity in leaves and roots were highest respectively.Under nitrate treatment,glutamate dehydrogenase(GDH)gradually increased activity in the leaves and stems,roots activity decreased.Glutamate dehydrogenase(GDH)activity in leaves reached the highest in 5 mmol/L level of ammonium and increased activity in stem,in contrast,roots activity decreased gradually with the increase of nitrogen concentration.(2)Metabolism of Populus simonii × P.nigra seedlings had relatively consistent trends with changes in nitrogen concentration under various nitrogen form treatment.With increasing nitrogen concentration,the free amino acid,soluble protein in different parts were increased,the content of soluble sugar in leaves changed little,the root were changed irregularly.The NH4+-N and NO3*-N content change of root changed with the external supply NH4+-N in the leaves decreased with increasing the external supply of nitrogen concentration,however,NH4+—N in stem increased.NO3-—N content in the leaves and stems was maintained at a more stable state.The carbon content of fluctuated in ammonium nitrogen treatment Total nitrogen and C/N ratios in nitrogen concentration of 10 mmol/L and 0.5 mmol/L maximum.C content of the whole plant decreased with increasing nitrate nitrogen treatment,N content trend contrast,C/N ratio in the nitrogen concentration of 1mmol/L at maximum.(3)Compared with the group treated with nitrate nitrogen,net photosynthetic rate(Pn),stomatal conductance(cond),transpiration rate(Trmmol),the content of intercellular CO2 concentration(Ci)and photosynthetic pigments were higher in ammonium-treated group of black poplar seedlings.but its photochemical efficiency(qP)low.The seedings of 5 mmol/L ammonium nitrogen the photosynthetic rate of strong,while nitrate nitrogen treatment response at 1 mmol/L treatment.With the increase of seedling biomass concentration of nitrogen increased gradually,reaching the highest in 5 mmol/L treatment.Populus seedlings under nitrate treatment had higher biomass and plant height.Leaf had smaller leaf area and greater leaf weight ratio under nitrate treatment,in other words,the leaf is small and thick in the form,In contrast,the performance of Populus simonii ×P.nigra leaf was large and thin under ammonium treatment.