Different Nitrogen Forms On The Photosynthetic Characteristics Of Betula Platyphylla And Fraxinus Mandshurica Seedlings

In recent years,most of the research on nitrogen nutrition has focused on crops,but less on trees nutrition.In order to explore the differences in the effects of different nitrogen forms on the growth and photosynthetic characteristics of tree seedlings,and the adaptive strategies for different nitrogen forms.Taking one-year seedlings of Betula platyphylla and Fraxinus mandshurica as the research objects,nitrate nitrogen,ammonium nitrogen and organic nitrogen were applied through pot experiments.By measuring the plant height increment,ground diameter increment,nitrogen mass fraction of leaves,stomatal characteristics of leaves,steady-state photosynthetic parameters and dynamic photosynthetic induction parameters of seedlings,chlorophyll fluorescence parameters of Betula platyphylla and Fraxinus mandshurica seedlings,two-factor analysis of variance was used to determine the effects of nitrogen forms and species on growth and photosynthetic indicators and their interactions,and the correlation between growth indicators and photosynthetic indicators was analyzed by Spearman rank correlation.The results are expected to provide reference for the selection of reasonable nitrogen fertilizer forms for the cultivation of Betula platyphylla and Fraxinus mandshurica seedlings in the northeast region.The main results are as follows:and two-factor analysis of variance was used to determine the effects of nitrogen forms and species on growth and photosynthetic indicators and their interactions.Spearman rank correlation was used to analyze the correlation between growth indicators and photosynthetic indicators.The results show that:（1）The effects of nitrogen form treatment and tree species and their interactions on seedling growth indicators were significant（P<0.05）,and the effects of nitrogen form on growth were significantly different between the two tree species（P<0.05）;For Betula platyphylla seedlings,nitrate nitrogen promoted growth increment and stomatal characteristics,ammonium nitrogen promoted plant height increment,leaf nitrogen mass fraction,and stomatal characteristics,while organic nitrogen promoted plant height increment and leaf nitrogen mass fraction.For Fraxinus mandshurica seedlings,both nitrate nitrogen and organic nitrogen promoted their growth indicators,while ammonium nitrogen promoted their growth increment.（2）The effects of nitrogen form treatment and tree species and their interactions on the photosynthetic response indexes of seedlings were significant（P<0.05）,while the effects of nitrogen form on photosynthetic induction were not significant（P>0.05）,but the effects of tree species on photosynthetic induction were extremely significant（P<0.001）;For Betula platyphylla seedlings,nitrate nitrogen promoted their maximum net photosynthetic rate(P_max),photosynthetic nitrogen use efficiency(P_NUE),and photosynthetic induction.Ammonium nitrogen promoted their water use efficiency(W_UE),P_max,P_NUE,and photosynthetic induction.Organic nitrogen promoted their P_max,P_NUE,and W_UE.For Fraxinus mandshurica seedlings,nitrate nitrogen promoted their P_NUE and W_UE,while ammonium nitrogen and organic nitrogen promoted their W_UE.（3）Tree species and the interaction between nitrogen forms and tree species had a significant impact on the chlorophyll content of leaves（P<0.05）.Nitrogen forms and tree species had a significant impact on the chlorophyll fluorescence parameters of seedlings（P<0.05）,but their interaction had no significant impact on the chlorophyll fluorescence parameters（P>0.05）.Nitrate nitrogen promotes the actual photochemical quantum efficiency of photosystem II(Ф_PSII)in Betula platyphylla seedlings,and apparent electron transfer rate(E_TR),ammonium nitrogen and organic nitrogen are promotedФ_PSII,maximum photochemical quantum efficiency of photosystem II（F_v/F_m）,E_TR.Nitrate nitrogen and organic nitrogen promote the growth of Fraxinus mandshurica seedlingsФ_PSIIand E_TR,ammonium nitrogen promotedФ_PSII,F_v/F_m,and ETR.Based on the above results,the effect of nitrogen forms on seedling growth is significant,and the effect of different nitrogen forms on seedling growth is different.Organic nitrogen promotes the increment of plant height and ground diameter,as well as the nitrogen content and stomatal characteristics of leaves,reduces the photoinhibition of seedlings in the light quality transition,and protects the light system II.Ammonium nitrogen is not conducive to the increment of seedling diameter,but ammonium nitrogen promotes the photosynthetic capacity of seedlings.