Effects Of Different Nitrogen Deposition On The Growth And Its Mechanism Of Sinocalycanthus Chinensis Seedlings

Seedlings of Sinocalycanthus chinensis were selected as study of objects.Four simulated nitrogen deposition levels:control(CK,0g·m^-2·a^-1),lower nitrogen(N1, 2g·m^-2·a^-1),medium nitrogen(N2,8g·m^-2·a^-1),and high nitrogen(N3,32g·m^-2·a^-1).After1 year from September 2016 to September 2017,we measured the growth characteristics,photosynthetic physiology,biomass and allocation and Non-structure carbohydrate of Sinocalycanthus chinensis seedlings,soil characteristics and soil microbial diversity among the different treatments.Analysis may respond to nitrogen deposition from the aspects of physiology,microbial diversity and so on to study the effects of nitrogen deposition the possible mechanism of Sinocalycanthus chinensis seedlings and the accumulation of non-structural carbohydrates in plants and distribution pattern,for understanding of the ecological adaptability of Sinocalycanthus chinensis,and then for the reasonable promotion and utilization of endangered plants of Sinocalycanthus chinensis provides reference.The main results are as follows:With the increase of nitrogen concentration,plant height,base diameter and number of leaves showed an increasing trend,and plant height,base diameter and number of leaves were significantly higher than the control group under medium nitrogen treatment.With the gradual increase of nitrogen deposition level,the average leaf circumference,average leaf area and average leaf length of seedlings were increased on the whole,and the treatment with N2 was the largest,which was significantly higher than the control.The ratio of leaf width to length reached the maximum at N3,and was significantly higher than that of other treatments.With the increase of nitrogen concentration,the leaf shape tended to be round.The specific leaf area N2 and N3 were significantly lower than CK and N1.Under N2 treatment,the average diameter of roots was significantly larger than that of other treatments,and the root volume CK was significantly lower than that of other treatments.Under N3treatment,the root length and specific root surface area N2 and N3 were significantly lower than that of CK and N1.Biomass of leaves,stems,roots and crowns and total biomass increased with the increase of nitrogen concentration,and N2 treatment was significantly higher than CK and N1.Leaf biomass ratio was negatively correlated with root biomass ratio and root crown ratio.Leaf biomass ratio was the lowest under N2treatment,significantly lower than CK and N3 treatment.Root biomass ratio and root to crown ratio were significantly higher in N2 than in CK and N3.There was no significant difference in stem biomass ratio with the increase of nitrogen concentration.The contents of starch and non-structural carbohydrates?NSC?in the leaves were all the highest with N2,while stem and root were the lowest under N3.In conclusion,with the aggravation of nitrogen deposition,it will have a negative effect on the growth of Sinocalycanthus chinensis seedlings to a certain extent,and affect the change of non-structural carbohydrates in plants,which reflects the adaptation of plants to living conditions.With the increase of the degree of nitrogen deposition,Sinocalycanthus chinensis seedlings leaf net photosynthetic rate of P_n under different nitrogen concentration presents a trend of reducing the rise,N1,N2 and N3 were significantly higher than that of CK,intercellular CO₂ concentration C_i after different nitrogen treatment,transpiration rate,stomatal conductance G_s,T_r under different concentration but is roughly upward trend after fall first,are the lowest in N2,and significantly lower than that of CK.Under different nitrogen treatments,there was no significant difference in the content of nitrogen in leaves,but the content of nitrogen in stems increased gradually with the increase of nitrogen concentration,and CK was significantly different from other nitrogen treatments.With the increase of nitrogen concentration,the content of nitrogen in the root increased first and then decreased.Under CK and N3 treatment,the content of nitrogen in the root was significantly lower than that under N1 and N2treatment.The content of nitrogen in root and leaf was significantly higher than that in stem,reaching more than 2 times of that in stem.The activities of soil catalase and urease activity first increased and then decreased with the concentration of nitrogen.Sucrase activity showed no significant difference at different nitrogen concentrations.Soil pH and organic matter decreased with the increase of nitrogen concentration.Ammonium nitrogen,nitrate nitrogen N2 and N3 in soil were significantly higher than CK and N1.Soil available potassium N2 and N3 were significantly higher than CK.The diversity and richness of bacteria were the highest under N2 treatment.The dominant bacteria groups of soil bacteria were Proteobacteria,Acidobacteria,actinobacteria and Gemmatimonadetes.Moreover,Proteobacteria had the highest abundance in different types of soil.Soil fungi AMF advantage bacterium group,the main phylumof Chytridiomycota,Glomeromycota,Rozellomycota,Chytridiomycota in different types of soil distribution by the highest abundance,but with the increase of nitrogen concentration showed a trend of increasing first and then decreasing.