Responses Of Typical Grassland Communities And Stoichiometric Characteristics To Mowing And Nitrogen And Phosphorus Addition In Inner Mongoli

Mowing is one of the important utilization methods of typical grasslands in Inner Mongolia.It affects the structure and function of grassland ecosystem by removing aboveground biomass.As an important improvement measure for degraded grassland ecosystems,nutrient addition(fertilization)can alleviate the limitation of soil nutrients and improve the productivity of grassland ecosystems.At present,a large number of studies have been carried out on the effects of mowing and nutrient addition on grassland ecosystems,but there is a lack of research on the response of grassland ecosystems to the interaction of mowing and nutrient addition.In this study,the typical grassland community in Inner Mongolia and its dominant species Leymus chinensis and Cleistogenes spuarrosa were taken as the main research objects,and the effects of mowing and nutrient addition on the community characteristics were discussed.On the basis of nutrient content,soil nutrient content and its stoichiometric characteristics,plant nutrient stoichiometry and nutrient resorption in response to mowing and nutrient addition are revealed.The research can provide theoretical support for the management practice and degradation restoration of typical grassland ecosystems in Inner Mongolia.Below are key research findings:(1)There were differences in the response of grassland community characteristics to mowing and nitrogen and phosphorus addition.Mowing significantly increased the community density,the biomass of Cleistogenes spuarrosa,species richness and the Shannon-Wiener index,and significantly reduced the litter content.Nitrogen and phosphorus addition increased the community coverage and the biomass of Cleistogenes spuarrosa,but had no significant effect on the community density and species diversity index(species richness,Shannon-Wiener index,Pielou index).There was a significant interaction between mowing and nitrogen and phosphorus addition on community biomass and the litter content.The biomass of Cleistogenes spuarrosa in both years was significantly positively correlated with the species diversity index,while the biomass of Leymus chinensis was significantly negatively correlated with the species diversity index(except the species richness in 2021).(2)Nitrogen and phosphorus addition significantly affected soil total phosphorus content,while soil organic carbon and total nitrogen content did not change much under each treatment,showing the characteristics of tight coupling between carbon(C)and nitrogen(N),which also made soil C: N tends to be stable.Phosphorus(P)addition and NP co-addition increased soil total phosphorus content and decreased C:P and N:P.N addition increased soil N content but did not reach a significant level.Nitrogen and phosphorus addition reduces soil p H and water content.N addition significantly increased soil ammonium nitrogen and nitrate nitrogen content.P addition significantly increased soil available phosphorus content,and NP co-addition significantly increased soil available nutrient content.When N or P nutrient was added alone,the corresponding soil available nutrient content was the highest.Mowing only increased soil C:P ratio,and had no significant effect on other soil stoichiometric characteristics.(3)The C content of plant leaves changed little under the influence of mowing and nitrogen and phosphorus addition.Mowing significantly increased the N and P content of the leaves of Cleistogenes spuarrosa,decreased its C:N and C:P,and only significantly increased the P content of the mature leaves of Leymus chinensis.Nitrogen and phosphorus addition significantly affects N,P content and C,N,P stoichiometric ratio in plant leaves(except N and C:N in mature leaves of Leymus chinensis).N addition increased plant leaf N content and N:P,and decreased C:N.P addition increased the P content of plant leaves and decreased C:P and N:P.The co-addition of NP increased the N and P content of plant leaves,and decreased the C:N and C:P of plant leaves.At the species level,the leaf stoichiometry of Cleistogenes spuarrosa was more sensitive to mowing and nitrogen and phosphorus addition.(4)The effect of mowing on nutrient resorption efficiency was weak,and nitrogen and phosphorus addition significantly affected plant nitrogen resorption efficiency(NRE)and phosphorus resorption efficiency(PRE).N addition significantly decreased plant NRE,P addition significantly decreased plant PRE,and NP co-addition significantly decreased both NRE and PRE.(5)Soil available nutrients and p H are the main soil environmental factors affecting plant stoichiometry.Soil available nitrogen was significantly negatively correlated with plant NRE,and significantly positively correlated with N content in mature and senesced leaves of plants.Soil available phosphorus was significantly negatively correlated with plant PRE,and significantly positively correlated with P content in mature and senesced leaves of plants.It indicated that nitrogen and phosphorus addition increased the content of available nutrients in the soil,thereby increasing the nutrient content of plant leaves,and at the same time reduces the NRE and PRE of plants.The increase of nutrient content in plant senesced leaves increased the nutrient content of litter into the soil and accelerated the flow rate of nutrients.It shows that the addition of nitrogen and phosphorus promotes the nutrient cycle between soil and plants,and changes the nutrient utilization strategy of plants,that is,plants tend to absorb more soil nutrients under the influence of nitrogen and phosphorus addition,and reduce the proportion of nutrients obtained through nutrient resorption.This study contributes to improving our understanding of the effects of grassland management practices on ecosystem nutrient cycling mechanisms.