Responses Of Plant Nutrient Cycling Characteristics To Nitrogen Regulation In A Peatland Of The Great Hing’an Mountains

As one of the important carbon sinks,peatland has rich carbon and nitrogen reserves and is sensitive to environmental changes.With the global warming,the freezing and thawing process in the north high latitude permafrost area has changed,making some organic matter decompose and release endogenous nitrogen,which affects the vegetation community structure and carbon sequestration potential in this area,and may change its carbon sink function.Therefore,based on field in-situ nitrogen addition experiment(which has been carried out for 9 years,the nitrogen addition concentrations are CK:0 g N m^-2·year^-1,N1:6 g N m^-2·year^-1,N2:12 g N m^-2·year^-1and N3:24 g N m^-2·year^-1),laboratory warming simulated and nitrogen addition experiments(temperature:10℃and 20℃;nitrogen addition concentrations are:CK:0 mg N g^-1,N1:2.5 mg N g^-1,and N2:5 mg N g^-1),this study took the peatland plants in Great Hing’an Mountains permafrost area as the research object,and analyzed the effects of nitrogen regulation on the plant community structure,plant growth characteristics,nutrient dynamics and the decomposition process of plant litters in the peatland.The main results are as follows:（1）Nitrogen addition significantly increased the height of Betula fruticosa in peatland and decreased the abundance and coverage of Chamaedaphne calyculata and Vaccinium uliginosum.With the increase of nitrogen concentration,the plant species diversity and richness in peatland decreased.Nitrogen addition can affect the plant community structure of peatland by affecting plant growth characteristics.（2）Nitrogen addition increased the chlorophyll content of Betula fruticosa,Chamaedaphne calyculata and Vaccinium uliginosum leaves in peatland,and the chlorophyll content was positively correlated with plant total nitrogen content and negatively correlated with C/N ratio.Low concentration nitrogen addition can promote plant photosynthesis,while high concentration nitrogen addition may be toxic to plants and inhibit plant photosynthesis.（3）Long term nitrogen addition increased the total nitrogen content of senescent leaves of peatland plants,decreased the total phosphorus content of peatland plants,decreased the C/N ratio of plants,and increased the C/P and N/P ratios.Nitrogen addition can alleviate the nitrogen limitation of plants to a certain extent,but aggravate the phosphorus limitation of plants,resulting in the joint limitation of nitrogen and phosphorus or completely limited by phosphorus.The nitrogen resorption efficiency decreased with the increase of nitrogen addition concentration,while the response of phosphorus resorption efficiency of different plants to the change of nitrogen nutritional environment was different.The nitrogen and phosphorus resorption efficiency of Betula fruticosa in peatland was significantly correlated with the total nitrogen content.Thus,in the long-term scale,nitrogen addition can enhance the ability of Betula fruticosa to obtain nutritional resources,making it occupy a dominant position,and then affect the peatland plant community structure.（4）The response of decomposition rates in different plant litters to nitrogen nutrition regulation was affected by the initial content of lignin in plant litters.The decomposition rate of Eriophorum vaginatum litter was faster than that of Sphagnum,and the increase of temperature significantly promoted the litter decomposition and CO₂ emission of Eriophorum vaginatum and Sphagnum.Nitrogen addition promoted the decomposition of plant litter of Eriophorum vaginatum,low nitrogen concentration（N1 treatment）promoted the decomposition of Sphagnum litter,but N2treatment inhibited its decomposition.The temperature sensitivity of decomposition in Eriophorum vaginatum and Sphagnum litters decreased with the increase of nitrogen concentration.Nitrogen addition increased the activities ofβ-glucosidase,sucrase and acid phosphatase in the Eriophorum vaginatum and Sphagnum litters,but the enzyme activities in the two plant litters were inhibited with the increase of temperature.The effect of increasing temperature and nitrogen addition on the decomposition of plant litters was mainly regulated by microorganisms.The abundance of bacteria and fungi was positively correlated with the decomposition constant and CO₂ release rate of Eriophorum vaginatum and Sphagnum litters,and fungi were more dominant in the early stage of decomposition.This study revealed the response mechanism of nutrient cycling characteristics（absorption,accumulation and release）of peatland plant in permafrost area to nitrogen nutrition regulation,which provided an important theoretical basis for predicting the dynamic changes of nutrients in northern peatland under future environmental changes.