Effects Of Soil PH Control On Vegetation Community And Its Nutrient Characteristics In Inner Mongolia's Grasslands

Soil acidity and alkalinity is the state of soil representing the concentration of hydrogen and hydroxyl ions,generally measured in p H units.Too high or too low soil p H changes the distribution and transformation of soil nutrients,thus leading to changes in the availability of nutrient elements needed for plant growth and development.Previous research on soil p H usually focused on the damage of acid rain to vegetation and soil and the related mechanism.In addition to soil acidification,too high soil p H value could cause soil alkalinity,resulting in poor soil permeability and heavy texture,which is not conducive to the growth and development of plants.Grassland is an important part of the terrestrial ecosystem.As a fragile and open ecosystem,grassland is vulnerable to global changes and unreasonable activities of human beings,resulting in a decrease or increase of soil p H value.Existing studies have focused too much on the nutrient characteristics of grassland in relation to factors of grazing,water and fertilizer addition and warming,etc.It is still unclear how plant community of different grassland types and soil nutrients to changing soil p H.In this study,three types of grassland(desert,typical and meadow grasslands)with different soil p H values in Inner Mongolia were selected in Hangjinqi,Xilinhot and Erguna.Manipulated acid and alkali additions with three levels were conducted in fields and then the vegetation dynamics,soil and plant nutrients were investigated in order to better understand how global change impacts the degraded grassland ecosystem.The main findings were as follows:(1)There are differences in plant community and nutrient characteristics of three grassland types under natural environment.The order of soil p H value is:desert>typical>meadow grassland.The soil organic carbon content of typical and meadow grassland were21.0 and 22.9 g/kg,respectively,which were significantly higher than that of desert grassland(5.62 g/kg),the total phosphorus content of the three grassland types ranged from0.383-0.412 g/kg,with no significant difference.The content of soil available nitrogen in three grassland types increased with the decrease of soil p H value from west to east.The content of nitrate nitrogen in desert,typical and meadow grassland was 3.38,7.68 and 10.9mg/kg respectively,and the content of ammonium nitrogen was 2.90,10.76 and 17.5 mg/kg respectively.The content of available phosphorus in typical grassland is 3.43 and 3.30mg/kg higher than that in desert grassland and typical grassland respectively.The species diversity of typical grassland was significantly lower than that of desert and meadow grassland.The contents of total nitrogen and phosphorus in leaves and roots of typical grassland were higher than those in desert and meadow grassland,and the contents of organic carbon were lower than those in desert and meadow grassland.(2)The additions of acid and alkali altered the soil p H value in all three grassland types affecting vegetation community soil and plant nutrients.The soil p H value in desert,typical and meadow grasslands decreased with adding acid but increased with adding alkali.In particular,the additions of high acid and alkali significantly affected soil p H.However,the responses of soil nutrients to acid and alkali additions varied in different grasslands.The availability of soil nutrients was in a more degree affected by acid and alkali additions than total soil nutrients.Topsoil was also affected in a more degree by acid and alkali addition than subsoil,showing a curvilinear relationship with acid and alkali.For the vegetation community of each grassland,alkali addition significantly reduced the above-ground biomass of desert and typical grassland,by 33.0-80.0 and 19.8-58.3 g/m~2,respectively.Meanwhile reduced the underground biomass of meadow grassland by 1.99-3.53 g/m~2,while acid addition had no significant effect on the biomass of three grassland.For plant nutrients,acid and alkali additions exerted different effects on grass and non-grass growth.Acid addition had no significant effect on the nutrient content of grass leaves,while alkali addition significantly increased the nutrient content of grass leaves in typical and meadow grasslands.Acid and alkali additions significantly increased the nutrient contents of non-grass leaves in meadow grasslands.Medium and high additions of acid and low addition of alkali significantly increased the total phosphorus content of plant roots in the soil layer of 0-10 cm in desert grassland.For root nutrients in the 10-30 cm soil layer,medium addition of alkali significantly reduced the root carbon in meadow grassland.Low and high additions of alkali significantly increased root phosphorus in meadow grassland.High addition of acid significantly increased the root nitrogen content in typical grassland.(3)The correlation results between each grassland community,nutrient characteristics and soil p H value are different from the performance after adding acid and alkali.The soil organic carbon and total nitrogen in the 0-10 cm soil layer of the desert grassland showed a significant convex correlation with the soil p H value,and the correlation coefficients were0.451 and 0.678,respectively.Ammonium nitrogen and available phosphorus in 0-10 cm soil layer of typical grassland,nitrate nitrogen and available phosphorus in 0-10 cm soil layer of meadow grassland,ammonium nitrogen of 10-30 cm soil layer in desert grassland,available phosphorus in 10-30 cm soil layer of typical grassland,all the above have a significant concave correlation with soil p H value.The aboveground biomass of desert grassland significantly decreased with the increase of soil p H value,the aboveground and underground biomass of typical grassland showed a convex and concave correlation with soil p H value,and the correlation coefficients were 0.609 and 0.228,respectively.Total nitrogen of Gramineae plants in desert grassland,total nitrogen and phosphorus of Gramineae plants in typical grassland,organic carbon and total nitrogen of non-Gramineae plants,total nitrogen and total phosphorus of Gramineae plants in meadow grassland,total nitrogen and phosphorus of roots in 0-10 cm soil layer of desert grassland,all the above have a significant correlation with soil p H value.These results indicated that there were differences in soil p H value,vegetation community and nutrient characteristics among three grassland types under natural environment conditions.The effects of acid and alkali addition on the community and nutrient characteristics of grassland ecosystem showed that the response mechanism of plant communities of three grassland types to the changes of soil p H value was mainly the influence of soil p H value on readily available nutrient of soil,thus changing the growth and development of plants and even the structural characteristics of vegetation communities.The difference between the vegetation community and nutrient characteristics after acid and alkali addition and the trend reflected by long-term soil p H changes was manifested in the difference in the balance mechanism of grassland ecosystem to cope with external environmental changes.Therefore,attention should be paid to the change of soil p H in the grassland management and the restoration and reconstruction of deteriorated grassland in the future.The basic research on the regional difference of soil p H in grassland ecosystem should be strengthened and prevention and control measures should be formulated according to local conditions in the future,so as to provide basic data and theoretical support for the degradation restoration and scientific management of grassland ecosystem under the background of global change.