Effects Of Nitrogen And Silicon Addition On Growth And Leaf Nitrogen Content Of Four Representative Species In Alpine Meadow

Elymus nutans,Kobresia capillifolia,Thermopsis lanceolata and Anemone rivularis were selected as four representative species to study the responses of those four species to different levels of nitrogen(0,30,60,90 g·m-2 respectively marked as N0,N30,N60,N90),silicon(0,4,8,12 g·m-2 respectively marked as Si0,Si4,Si8,Si12)and nitrogen combined with silicon addition in alpine meadow.Our purpose was to figure out the effects of nitrogen and silicon addition on plant height,abundance,leaf nitrogen content,net photosynthetic rate and aboveground biomass and provide scientific basis for fertilizing in alpine meadow.The main conclusions were as follows:(1)With nitrogen addition alone,the plant height of E.nutans and T.lanceolata were highest at N60.K.capillifolia's and A.rivularis' reached the maximum at N90;With silicon addition alone,the plant height of K.capillifolia,T.lanceolata and A.rivularis peaked at Si4.When nitrogen combined with silicon added,there was a significant increase of E.nutans' and A.rivularis' at N30Si8.K.capillifolia's height increased significantly only at N60Si4.Then T.lanceolata's height reached the maximum at N60Si8.(2)When nitrogen added,abundance of E.nutans,K.capillifolia,and T.lanceolata peaked respectively at N60,N90 and N30.Well,nitrogen addition made no sense on the A.rivularis'.With the concentration of silicon increased,the abundance of E.nutans appeared to decline when T.lanceolata's and A.rivularis' continued to grow,and K.capillifolia's was highest at Si8;When nitrogen combined with silicon added,there was a sharp reduction of E.nutans' abundance but a significant increase of A.rivularis' with Si12 addition.K.capillifolia's had a rise at N30Si8 and N60Si4.T.lanceolata's reached the maximum at N30Si8.(3)Nitrogen addition alone could significantly increased leaf nitrogen content of the 4 species;Silicon addition made no sense on A.rivularis' but increased leaf nitrogen content of the other 3 species.E.nutans' and K.capillifolia's peaked at N60Si8,well,T.lanceolata's and A.rivularis' had no change at the same time.(4)Either nitrogen or silicon added alone,the net photosynthetic rate of those 4 species was all improved.E.nutans',K.capillifolia's and A.rivularis' all reached the maximum at N60Si8;well T.lanceolata's peaked at N30Si8.(5)Aboveground biomass of E.nutans and A.rivularis were highest at N60,then T.lanceolata's reached the maximum at N30,well,the K.capillifolia's had been rising with the concentration of nitrogen increased;There was an increase of E.nutans' at Si4,T.lanceolata's and K.capillifolia's peaked at Si8,the aboveground biomass of A.rivularis was highest at Si12.When nitrogen combined with silicon,E.nutans' and A.rivularis' reached the maximum at N60Si8,the aboveground biomass of K.capillifolia also significantly increased at the same treatment.Then,T.lanceolata's was highest at N30Si8.To this study,the leaf nitrogen content,net photosynthetic rate and the sum of aboveground biomass of E.nutans and K.capillifolia achieved the best level while the aboveground biomass of T.lanceolata was precisely at a lower level at N60Si8.Although the A.rivularis' was significantly increased under this treatment,it had little effect on the grazing,and the species diversity of alpine meadow could be maintained better with it.To sum up,applying nitrogen to promote the growth of E.nutans and K.capillifolia –two high quality forage grass in Tibetan Plateau,consideration should be given to the decrease in biodiversity and other negative effects caused by long-term single application of nitrogen.Well,silicon added properly not only made the aboveground biomass of the two kinds of grass go to a step further,but also settled above-mentioned problem to some extent.In this experiment,N60Si8 could get the better result among other treatments.