Effects Of Simulated Acidification On Soil Chemical Properties And Plant Nutrient Uptake In A Meadow Grassland

S deposition is the main contributor of global acid deposition,which has negatively affected the structure and functions of the terrestrial ecosystems,and has been a hot scientific issue in environmental sciences,global change ecology and ecosystem ecology.S deposition has almost doubled over the past two decades in the meadow grassland area in Northeast China.However,there is a lack of systematic research on the effects of soil acidification induced by S deposition on carbon over and nutrient cycling in grassland soil-plant systems.Based on a simulated soil acidification experiment through S addition(0,1,2,4,6,8,10 t S hm^-2)established in Inner Mongolia meadow grassland in 2019,this paper systematically investigated the oxidation rate of S,soil acidification properties,soil physio-chemical properties,soil nutrient availability and stoichiometric ratios,and nutrient absorption and element stoichiometry of plant species.The main results are as follows:（1）S addition significantly decreased soil p H,while increased soil electrical conductivity（EC）.S addition increased total S,water-soluble S,adsorbed S and insoluble S in topsoil.The three inorganic S fractions were negatively correlated with soil p H and positively with soil EC.The oxidization rate of S was decreased with exogenous S addition rates.The exogenous S input was mainly oxidized to plant available Ca Cl₂extracted inorganic S（water-soluble and weak adsorptive S）and Ca（H₂PO₄）₂extracted inorganic S（strong adsorptive S）,while the proportion of oxidized HCl extracted inorganic S（insoluble S）was very low.（2）S addition significantly increased soil exchangeable H⁺and Al³⁺and the total exchangeable acids.it was found that soil ANC with a reference p H of 4.0(ANC_{p H4.0})was significantly decreased with S addition rates.The ANC from the initial p H（6.27–4.26）of the soil solution in the S addition treatments decreased by 1 p H unit（it can also be called soil acid buffering capacity）was increased with the increasing S addition rates,indicating that the soil acid buffering system changed from exchangeable base dominated system to a combination of exchangeable base with iron-aluminum oxide system.S addition significantly decreased the content of exchangeable base cations Ca²⁺,Mg²⁺,K⁺,and Na⁺and soil exchangeable Ca/Mg and exchangeable Ca/K.（3）S addition had no significant effect on soil total C,N and P,while significantly increased soil available P and S.S addition significantly activated soil micronutrient Fe,Mn,Cu and Zn.Soil available trace micronutrients Fe,Mn,Cu were negatively correlated with soil p H,but positively correlated with soil EC.S addition significantly decreased soil available Fe/Mn,while increased soil available Mn/Zn and Mn/Cu ratios.（4）Soil acidification had no significant effect on C and N,increased S,while decreased P concentrations in the dominant plant species Leymus chinensis,Stipa baicalensis or Carex chinensis in the meadow grassland.S significantly increased plant N/P ratio,but decreased P/S and N/S ratios.Differential responses were found on the absorption of base elements by dominant plant species to soil acidification.Soil acidification increased Ca/Mg in L.chinensis,and Mg/K in C.chinensis,but decreased Mg/K in L.chinensis.Significant effects of soil acidification on plant micronutrient uptake were found among various plant species.Soil acidification significantly promoted plant Mn uptake but inhibited plant Fe uptake,while the stoichiometric ratios of plant micronutrients were also significantly changed under soil acidification conditions.