Effects Of Nitrogen And Phosphorus Addition On Litter Decomposition In Hulunbuir Meadow Grasslan

The increase of nitrogen（N）deposition makes the input of N and phosphorus（P）in the grassland ecosystem unbalance,which will affect the nutrient acquisition of different functional plants in the grassland,and then affect the nutrient cycle of the grassland plant community.Litter decomposition is a key process of nutrient cycle in terrestrial ecosystems,and it is also the main source of soil carbon（C）pool and an important basis for maintaining soil fertility,and is of great significance to the global C cycle.This study relies on the nitrogen and phosphorus addition control experimental platform of the Erguna Forest Steppe Transition Zone Ecosystem Research Station of the Shenyang Institute of Applied Ecology,Chinese Academy of Sciences.The platform applies two types of phosphorus fertilizers,namely potassium dihydrogen phosphate and superphosphate.A phosphate fertilizer was set with 6 addition levels(0,2,4,6,8,10 g m^-2),which interacted with the nitrogen fertilizer as ammonium nitrate(0,10 g m^-2).Taking Leymus chinensis,Cleistogenes squarrosa and Thermopsis lanceolata as the objects,the net bag decomposition method was used to study the effect of nitrogen and phosphorus supplementation on the decomposition of litter.The main conclusions as follows:（1）During the 3-year decomposition process,the decomposition rates of Leymus chinensis,Cleistogenes squarrosa and Thermopsis lanceolata were different,and the decomposition rates from high to low were:Thermopsis lanceolata>Cleistogenes squarrosa>Leymus chinensis;（2）The process of litter decomposition was affected by both internal factors（plant initial nutrient content）and external factors（soil nutrient addition）,and nutrient addition had a greater effect on promoting litter decomposition than internal factors;（3）In terms of external factors,nutrient addition significantly promoted the decomposition of three kinds of litter;in terms of internal factors,addition of P promoted the decomposition of three kinds of litter,and addition of N promoted the decomposition of litter of Leymus chinensis and C.litter decomposition;（4）P addition significantly shortened the half decomposition time and 95%decomposition time of litter,and the effect of high P addition was more obvious;（5）N addition inhibited the release of N element in the later stage of decomposition of Leymus chinensis and Cleistogenes squarrosa,and had little effect on the early stage of decomposition.P addition inhibited the release of P element in litter,and the inhibition effect of high P addition was more obvious;（6）Application of potassium dihydrogen phosphate is shorter than that of superphosphate litter decomposition.