Effect Of Nitrogen Additions On Soil Microorganisms And Ecological Stoichiometry Of Soil-Plant Of Bothriochloa Ischaemum

This experiment is carried out in the loess plateau, taking the typical herbs Bothriochloa ischaemum as the research object. There are 4 levels of nitrogen addition treatments: bare land(BL), 0(CK), 2.5(N1), 5(N2), 10(N3) gNm-2 a-1. Non-structure carbon, soil water soluble organic matter and its spectral characteristics, soil microbial characteristics and Bothriochloa ischaemum- soil ecological stoichiometry was studied. The main conclusions are as follows:Short-term nitrogen addition does not have a significant impact on plant mineral elements content, just have a impact on vegetation aboveground N: P.Apart from the non-significant effect on aboveground plant soluble sugar content, the effect of nitrogen addition on both aboveground and underground starch and non-structural carbohydrates and underground soluble sugar content were significant; And with the increase level of nitrogen addition, Bothriochloa ischaemum, underground parts of soluble sugar,starch and non-structural carbohydrates were rise trend and then reduced after the first; The starch content and non-structural carbohydrates of aboveground plant peaked in N1, soluble sugar, starch and total non-structural carbohydrates of underground plant have reached the maximum in N2.Water-soluble ammonium nitrogen and nitrate nitrogen are influenced by nitrogen addition significantly; With the increase of nitrogen addition level, water soluble organic nitrogen to have a rising trend and then a decling trend; With the increase of nitrogen addition level, the percentage of content of soil water soluble organic carbon and water soluble organic carbon on the total organic carbon were significantly reduced.Uv-vis spectra and the characteristic parameters and fluorescence spectrum have consistent results:in low level of nitrogen addition condition N1, DOM humus soil change is not obvious; While high level of nitrogen addition will promote the soil humus of DOM structure, and it tends to be complicated, make its molecular weight is higher, the degree of humification.Low level of nitrogen addition promote the growth of microorganisms and microbial respiration, add microbial biomass carbon and nitrogen content; High level of nitrogen addition inhibite microbial growth and microbial respiration, reduce microbial biomass carbon, nitrogen. With the increase level of nitrogen addition bacteria microbial community diversity and evenness increase, while the diversity of microbial communities reduce, butbasicly it did not change the microbial community structure.Appropriate nitrogen addition N1(2.5 g N m-2a-1) increases the content of soil microbial of Bothriochloa ischaemum effectively, promote the microbial diversity, and contribute to the stability of the loess plateau soil ecosystem. But more important is that plant biomass nitrogen reduce, microbial community is restrained. In addition, N1 is considered as tolerance values for the loess plateau soil microbial community.Nitrogen addition have a significant impact on soil carbon, nitrogen, phosphorus chemical stoichiometry, and soil water soluble organic carbon:organic nitrogen, microbial biomass carbon: nitrogen and the carbon:nitrogen use efficiency. Although nitrogen addition influence the soil, underground part and aboveground part of Bothriochloa ischaemum as well as the microbial stoichiometric, but the whole ecosystem under the levels of this experiment is homeostasis.