Effects Of Different Stimulated Nitrogen Deposition Levels On The Growth And Physiological Characteristics Of Mulberry Seedlings

Mulberry(Morus alba L.)has a strong adaptability to drought,saline-alkali and other abio logical stress.At the same time,mulberry trees can produce high economic benefits.In recent years,mulberry seedlings have been popularized in saline-alkali land area of Heilongjiang province for vegetation restoration and the development of rural economy.Nitrogen deposition can be intercepted by plant canopy.In order to explore the response mechanism of the growth and physiological and biochemical characteristics of mulberry seedlings to nitrogen deposition,the one-year-old mulberry seedling(Morus alba L.cv.Qiuyusang)were chosen as experiment materials,three nitrogen deposition levels were set:low-nitrogen(LN,4 mg·L-1),medium-nitrogen(MN,8 mg·L-1),high-nitrogen(HN,16 mg·L-1).Distilled water treatment was set as control(CK).The effects of simulated nitrogen deposition on the growth,photosynthetic characteristics,nitrogen metabolism and leaf anatomical structure of mulberry seedlings were studied.The main results were as follows:The growth and physiological and biochemical characteristics of mulberry seedlings were significantly affected by the change of nitrogen deposition level,and the growth and physiological status of mulberry seedlings under LN treatment had little difference with control.The non-photochemical quenching coefficient(NPQ)of mulberry seedlings under MN treatment was significantly lower than that of control.The total chlorophyll content,number and size of chloroplasts,the thickness of the palisade tissue,total biomass,plant height,leaf area,leaf mass per unit area(LMA),root activity,maximum net photosynthetic rate(Pnmax),stomatal conductance(Gs),actual photochemical efficiency(cOPS II),apparent electron transfer rate(ETR),nitrate reductase(NR)activity,glutamine synthetase(GS)activity and glutamic acid synthase(GOGAT)activity were significantly higher than those of control,LN treament and HN treatment.Under HN treatment,the non photochemical quenching coefficient(NPQ)of mulberry seedlings was significantly higher than that of control.The total chlorophyll content,root system activity,Pnmax,total biomass,photosynthetic nitrogen-use efficiency(PNUE),NR activity,GOGAT activity and palisade tissue thickness were significantly lower than those of the control,the cell membrane permeability and the number of starch grains in chloroplasts increased,and the grana lamellae of chloroplasts were stacked loosely,the number of grana decreased,the structure of granular membrane was not clear.The above results showed that the suitable level of simulated nitrogen deposition treatment(medium nitrogen)was beneficial to enhance photosynthetic capacity of leaves of mulberry seedlings,and promote nitrogen metabolism,and was beneficial to the accumulation of biomass.HN treatment affected the stability of physiological metabolism in mulberry seedlings,and HN treatment led to destruction of the chloroplast structure of mulberry seedlings and the abnormal photosynthesis of chloroplasts,which resulted in negative effect on the growth of mulberry seedlings.