Eco-physiological Characteristics Of Acer Saccharum Seedlings Under Nitrogen Deposition

The increase of atmospheric nitrogen deposition not only affects the growth and development of plants,but also impact on their photosynthesis of organic matter and chlorophyll fluorescence characteristics.To evaluate the effects of simulated nitrogen deposition on growth and physiological metabolism of Acer saccharum seedling,NH₄NO₃solution as the sole nitrogen source,the determination of control(CK,0 g·m^-2·a^-1),low-N(N₅,5g·m^-2·a^-1)and high-N(N₁₀,10 g·m^-2·a^-1)three levels,growth,biomass,leaf N content,leaf photosynthetic rate and chlorophyll fluorescence parameters of A.saccharum seedlings for 2 years old,analysis the relationship between the changes and nitrogen deposition.The results showed that:（1）N supply significantly promoted the tree height,stem diameter and biomass of A.saccharum seedlings,the maximum value was N₁₀,the order was N₁₀>N₅>CK（P<0.05）.（2）The monthly dynamic changes of biomass allocation ratio of A.saccharum seedlings significantly during the experiment（P<0.01）.Among them,root weight ratio and root shoot ratio was increased first and then decreased,in the early of nitrogen addition,the maximum value was in N₁₀;in the late of nitrogen addition,the maximum value was in CK.However,the stem weight ratio and leaf weight ratio decreased first and then increased,and in the late of nitrogen addition,N₅ and N₁₀ increased significantly（P<0.01）,and the maximum value was in N₁₀.（3）From May to July,the leaf N content and relative chlorophyll content（SPAD）of A.saccharum seedlingsincreased with the increase of nitrogen deposition contents.,the maximum value was N_10。There were significantly difference between the content of leaf N and SPAD in N₅,N₁₀ treatment and CK（P<0.01）.The values were respectively higher than CK about（0.39±0.08）mg,（0.44±0.06）mg;（5.94±0.28）mg,and（7.29±0.25）mg.（4）Nitrogen application significantly increased Pmax,LSP and LCP,Pn,Gs and E of A.saccharum seedlings,the maximum value is in N10;C_i was extremely different significantly between the nitrogen treatment groups（P<0.01）,and the maximum valuewas in CK.The WUE in N₅ and N₁₀ treatment was significantly higher than CK of 16.97%,9.77%.（5）From 8:00 O’clock to 20:00 O’clock,under different nitrogen levels,the diurnal changes of photosynthetic rate（Pn）,stomatal conductance（Gs）,and water use efficiency（WUE）of A.saccharum seedlings were double peak at 10:00 and 14:00,respectively.Thus,the diurnal change of transpiration rate（E）was single peak at 12:00.（6）From May to July,the value of chlorophyll fluorescence parameters,such as,FV/FM,yield,FV/F0,qP of A.saccharum seedlings increased with the increase of nitrogen deposition,the order was N₁₀>N₅>CK.In July,the maximum value of F_V/F₀was in N_10,and the value of significantly higher than that of CKwas 0.37±0.008,there was no significant difference between N₅ and N₁₀ treatments.QN was negatively correlated with qP,and the minimum value in N₅.Under the same nitrogen concentration,compared with May,FV/F0was a significant increase trend in june（P<0.01）,and respectively increased by 0.85±0.0.9,1.65±0.28,and 1.42±0.21.In conclusion,nitrogen addition promoted height,ground diameter,total biomass,leaf N content,SPAD,Pmax,LSP,LCP,Gs,E,WUE and Fv/F₀ of A.saccharum seedlings（P<0.01）,under N₁₀0 treatment,the effect was the most significant;but Under different N treatment,between june and july,chlorophyll fluorescence parameters F_V/F_M and Yield did not change significantly（P>0.05）.