Effects Of Simulated Nitrogen Deposition And Acidification On Soil Properties In Yunwu Mountain Grassland

The Yunwu Mountain Grassland Nature Reserve in Ningxia is the most well protected " Typical Grassland Nature Reserve of Stipa Bungeana " in the northwest of China,covering an area of 7000 hectares.It provides scientific basis and experimental sites for vegetation restoration,soil and water conservation and environmental control of Loess Plateau,natural vegetation restoration in semi-arid areas of China and the study of elements cycling mechanism of grassland ecosystem.Many scholars have done a lot of research on grassland ecosystem,mainly focusing on the change of soil moisture and carbon,nitrogen,phosphorus content,or the impact of different vegetation on soil nutrient elements and physical-chemical properties.However,the research on the response of carbon,nitrogen and phosphorus cycle and microbial biomass to nitrogen deposition and soil acidification in grassland ecosystem is relatively less.The paper based on the long term experiment of Yunwu Mountain Grassland Nature Reserve in Guyuan,Ningxia,measuring the physical and chemical properties of soil and the content of different forms of soil carbon,nitrogen and phosphorus and study on soil microbial characteristics of Yunwu Mountain Grassland by real-time PCR in order to study the effect of simulated nitrogen deposition and acidification on soil carbon,nitrogen and phosphorus content,microbial biomass and microbial characteristics.In this paper,eight typical treatments are selected,which are divided into two categories:1.Nitrogen deposition(CK,N,N+W);2.Acidification(S0,S1,S2,S3,S4).The physical and chemical properties of soil and the abundance of bacteria,archaea,ammoxidation bacteria,ammoxidation archaea,methane-oxidizing bacteria(pmoA),nitrogenase ferritin gene(nif-H),nitrite reductase(nir-S)were determined.The relationship between soil microbial abundance and environmental factors was explored by redundancy analysis.The following are the main conclusions of this paper.(1)Nitrogen application increased the content of soil soluble organic carbon andnitrate nitrogen,,decreased the content of TC,TN and ammonium nitrogen,,inhibited the soil microbial biomass,increased the content of TP,AP,OP,respiratory quotient and mineralized nitrogen.The effects of nitrogen deposition on soil organic carbon,total carbon and total nitrogen were positive or negative growth or no significant change,which may be related to the time and concentration of nitrogen application.Long-term application of nitrogen can reduce soil microbial biomass,and the accumulation of nitrogen may have toxic effect on soil microorganisms and inhibit microbial activity.The effects of nitrogen application and acidification on respiration rate have not been determined.Nitrogen application increases organic carbon in the soil,accelerates plant growth,and litter enters the soil to become organic matter,which becomes a microbial carbon source to promote microbial respiration.When soil nutrients are obtained by plants,the decrease of available organic matter in soil made the activity of microorganism is decreased.(2)Acid application reduced soil pH,promoted the content of organic phosphorus(OP),microbial biomass phosphorus(MBP),ammonium nitrogen and respiration rate.Soil total carbon(TC),total nitrogen(TN),microbial biomass carbon(MBC)were related to acid concentration.(3)Nitrogen application and nitrogen application with temperature increasing treatment increased the abundance of soil bacteria and archaea to 108 copies per gram,decreased the abundance of methane-oxidizing bacteria,nitrogenase ferritin and nitrous reductase genes in the soil.Acid treatment reduced the abundance of Archaea in the soil but promoted the abundance of soil bacteria,nitrogenase ferritin and nitrous reductase genes.There was a positive correlation between the abundance of methanotrophic bacteria and the contents of soil microbial biomass nitrogen,ammonium nitrogen.There was little correlation between the abundance of nitrogenase ferritin gene,nitrous reductase and the content of nitrate nitrogen.Soil microbial biomass nitrogen and ammonium nitrogen content,total phosphorus and available phosphorus content were positively correlated significantly.There was a significant positive correlation between Archaea abundance and N:P,MBC,pH,MBN.The microbial abundances of ammonia oxidizing bacteria and ancient ammonia oxidizing bacteria were positively correlated with soil C/P ratio,contents of available P and nitrate nitrogen,The correlation between the gene abundance of methane-oxidizing bacteria and soil microbial biomass nitrogen is very weak.(4)Nitrogen deposition increases litter input,reduces soil carbon output,promotes soil humus and stable carbon formation which affects soil physical and chemical properties and element stoichiometric ratio,increases soil nitrogen content,provides nutrition for soil microorganisms,also increases soil microbial activity.Different types of microorganism have different nature and the response of microbial quantities and types to nitrogen deposition is also different,resulting different response of microbial biomass to nitrogen deposition after nitrogen application.