The Effects Of Nutrients Addition On Aboveground Productivity,Community Composition And Functional Traits Of Leymus Chinensis Grassland

The grassland ecosystem is the largest terrestrial ecosystem in China.Due to the interference of human activities such as overgrazing and agricultural reclamation,grassland is facing degradation.Therefore,taking effective management and restoration measures is of great significance to the sustainable development of grassland.Fertilization is an effective management method of grassland that has a great impact on yield.In order to explore the response process of grassland productivity to nutrient addition,this paper takes Songnen grassland as the research object,adopts a three-factors nesting experimental design,and sets up nitrogen(N:control,pure nitrogen 100 kg·ha^-1·year^-1),phosphorus(P:control,pure phosphorus100 kg·ha^-1·year^-1),potassium(K:control,pure potassium 100 kg·ha^-1·year^-1)addition experiment.The effects of different nutrient additions on aboveground productivity,species diversity and plant functional traits were discussed.1)Compared with the control（CK）,the addition of N can significantly increase the total aboveground biomass.The combined addition of NPK had the greatest impact on the total aboveground biomass,which was significantly increased by 99.2%compared with the control treatment.Secondly,N and NP were added,and the total biomass was significantly increased by 74.8%and 53.4%,respectively,compared with CK treatment.Adding N,NP and NPK can significantly increase the total biomass of grassland.When P,K and PK are added,there is no obvious effect on the total biomass.The biomass of Gramineous species increased significantly with the addition of N,NK,and NPK,which were significantly increased by 104.9%,139.9%,and 118.4%,respectively,compared with CK treatment.The biomass of Leguminous species was significantly reduced by 72.3%,82.9%,55.6%,46.2%and 50.1%under the addition of N,NP,NK and NPK and PK,respectively.NP had the greatest impact on the biomass of Leguminous species.The biomass of weeds was the most under NP addition,followed by NPK and N addition,which significantly increased by 136.8%,109.3%and 88.3%compared with CK treatment.The response trend of litter to different nutrients is consistent with the change of total aboveground biomass.The addition of N,NP and NPK significantly increased the litter by 74.8%,74.4%and90.8%,respectively.2)Compared with CK,the addition of NPK,NK,NP,and N significantly reduced the species richness of the community,which was significantly reduced by48.3%,44.8%,48.3%and 51.7%compared with CK treatment.The addition of PK,P and K had nosignificantly effect on the species richness.The total coverage of the community when NPK was added was the largest,followed by N,which was significantly increased by 30.33%and 28.83%compared with CK treatment.With the addition of N and NK,the coverage of Gramineae significantly increased by 26.88%and 21.66%,while the coverage of Legumes decreased significantly by 13.13%and14.63%.Gramineae coverage and the coverage of Legumes were negatively correlated with nutrient addition.The coverage of weeds only had a significant effect under the addition of N,which was significantly increased by 15.08%compared with CK.When K was added,the aboveground biomass of grassland had significantly positive correlation with the coverage of Legumes,when PK was added,the aboveground biomass had significantly positive correlation with the coverage of Gramineae,and when NPK was added,the aboveground biomass had significantly positive correlation with the coverage of weeds.There is no significant correlation between aboveground biomass and species richness.3)The effect of nutrient addition on plant functional traits is mainly reflected in the following aspects:（1）The plant height community weighted means（CWM）was the largest when NPK was added,which was a significant increase of 112.94%compared with CK treatment,followed by NP and N addition,which were significantly increased by 100.96%and 80.83%respectively compared with CK treatment.（2）The plant leaf area community weighted means（CWM）,leaf thickness CWM,and chlorophyll（a+b）content CWM all increased significantly with the addition of N,NP,NK,PK,and NPK.There is no obvious effect on leaf traits.The leaf dry matter content CWM was the largest when NPK was added,and it was significantly increased by 33.68%compared with CK treatment.The addition of other nutrients had no obvious effect on it.In summary,the addition of N and the combination of N elements（ie,NP,NK and NPK）are beneficial to the improvement of grassland aboveground productivity.Especially the three nutrient addition methods of N,NP and NPK are more significant for improving grassland aboveground productivity.The addition of N and the combination of N elements（ie,NP,NK,and NPK）changes the species richness and community composition,which is reflected in the decrease of species diversity,and the addition of N and NPK helps improve community coverage.Nutrient addition changes the functional traits of plants:the addition of NPK increases the dry matter content of the leaves,and the increase in the structure of the leaf per area leads to an increase in leaf life;the addition of N,NP and NPK increases the plant height,significantly increase the leaf area,chlorophyll（a+b）content and leaf thickness,enhance the competitiveness of grassland plants against light sources and the photosynthetic capacity of plant leaves,thereby increasing the aboveground productivity of grassland plants.Through this study,the effects of nutrient addition on grassland aboveground productivity,species diversity and plant functional traits are clarified,and provides theoretical basis for the restoration of degraded grassland in Songnen area and the establishment of scientific grassland management measures.