Effects Of Nitrogen Application On The Individual Characteristics,Group Structure And Productivity Of Leymus Chinensis

Leymus chinensis is a dominant species in saline-alkaline grassland of Northeast China.It played an extremely important role not only in development in stockbreeding,but also in degraded grassland restoration,reconstruction and ecological management.Therefore,how the group structure of Leymus chinensis influencing productivity is crucial for improvment in productivity in this region.Here,we conducted an experiment applying pure nitrogen(0 kg/hm2,45 kg/hm2,90 kg/hm2,135 kg/hm2,180 kg/hm2)once every half month during the spring(May,June)and the summer and autumn of last year(July,August and September),to explore the effect of different nitrogen application time and level on individual characteristics,group structure,and productivity.Results are as follows:1.In spring,summer and autumn,different nitrogen application timing and application level have an significant effects on the individual characteristics(but in addition to the number of stem sections).With the increment in nitrogen application rate,the height,total stem length,leaf length,leaf number of individual plant,leaf area of single leaf and specific leaf area significantly increased.While the dry matter content of leaves was opposite,it decreases with the increase of nitrogen application rate.Effects of fertilization on individual characteristics in spring is better than those in summer and autumn.2.In spring,summer and autumn,different nitrogen application timing and application level have an significant effects on the vertical structure(leaf area index).With the increment in nitrogen application rate,the leaf area index significantly increased.And effects of fertilization on leaf area index in spring is better than those in summer and autumn.In spring,summer and autumn,the hierarchical structure of individual plants is different at varied nitrogen application timing and level.Combined individual characteristics,productivity and nutritional elements,the best individual plant type structure occured at N4 level on May 30 th in spring.That is,the upper biomass of individual was significantly higher than the lower one.The largest biomass was in 30-40 cm above the ground and the further down,the less biomass,showing an inverted pyramid structure.In spring,summer and autumn,different nitrogen application timing and application level have significant effects on the horizontal structure(density).The density increases with the nitrogen rate,and the effect of fertilization on the density in summer and autumn is greater than that in spring.3.In spring,summer and autumn,different nitrogen application timing and application level have an significant effects on the productivity(stem biomass,leaf biomass,total productivity).With the increment in nitrogen application rate,the stem biomass,leaf biomass and total productivity increased,and the effect of fertilization on productive forces in spring is greater than that in summer and autumn.4.The nitrogen application timing and level significant influenced on C content,N content,C:N,and N:P.Whereas,there was no significant effect on P content and C:P.With the increment in nitrogen application rate,except for P content,C:N were reduced,the N content,C:P,N:P were all increased.In summary,nitrogen addition imporved the individuals growth and increased the productivity of Leymus chinensis.It redistributed energy of the individuals and changed population vertical structure.We concluded that in spring May 30 th,the applies 180 kg/hm2 nitrogen fertilizer can optimize group structure,individual characteristics,and in spring May 15 th,the applies 180 kg/hm2 nitrogen fertilizer can optimize productivity.This experiment provide reliable data for the rational group structure construction,and provide clues for the optimum nitrogen fertilizer application rate in Leymus chinensis grassland in Songnen plains.