Effects Of Simulated Nitrogen Deposition On Soil AMF And Understory Herb Community Structure And Diversity In Korean Pine Plantation

The increase in nitrogen deposition with the development of agriculture and industry has caused widespread concern among scientists,and although emission reduction policies have slowed nitrogen emissions in Europe and North America,the threat to biodiversity cannot be ignored.Arbuscular mycorrhizal（AM）fungi play an important role in the establishment and maintenance of plant communities in forest ecosystems,and their distribution and diversity have critical ecological functions.Herbaceous plants in forest ecosystems are major contributors to forest ecosystem diversity,and herbaceous plants are critical to the symbiotic relationship of AM fungi,which,through their symbiotic relationship with forest herbaceous plants,can provide nitrogen and other nutrients needed by plants,as well as enhance disease resistance and adversity adaptation.However,as nitrogen deposition increases,the nitrogen content in forest ecosystems also increases.This can have an impact on the growth and distribution of AM fungi,which in turn affects the ecological function and diversity of forest ecosystems.Increased nitrogen deposition may lead to changes in the symbiotic relationship between AM fungi and herbaceous plants,thus affecting the ecological function and diversity of forest ecosystems.In order to analyze the effects of long-term N addition on AM fungi and understory herbaceous plants in Korean pine（Pinus koraiensis）plantations in northern China,the present study was conducted to investigate the soil chemical properties,glomalin-related soil protein,and the soil chemistry of Korean pine plantations with different concentrations of NH₄NO₃(0、20、40、80 kg N ha^-1 yr^-1)applied for 7consecutive years.We investigated soil chemistry,glomalin-related soil protein（GRSP）content,AM fungal community structure and diversity,understory herbaceous community structure and diversity,and fine root biomass to investigate the biochemical indicators.The experiments were conducted to provide a theoretical basis for forest stability in the context of atmospheric nitrogen deposition and even global climate change.The main results of the study are as follows.1.Long-term nitrogen addition affects the soil properties of Korean pine plantations.Among them,the chemical properties: significantly reduced the soil pH value（-0.49）,increased the content of total nitrogen and ammonium nitrogen in the soil,reduced the content of nitrate nitrogen in the soil,and caused fluctuations in phosphorus（P <0.05）;physical properties: Nitrogen treatment increased the content of total glaucomycin extracted,changed the distribution of soil aggregates,and improved the stability of soil aggregates.2.Nitrogen addition changed the AM fungal community composition.The distribution of species in each treatment group was changed,and the Glomus genus affected by nitrogen deposition was more adapted to the acidic soil environment of the long-term high nitrogen treatment group(80 kg N ha^-1 yr^-1);with the increase of nitrogen concentration gradient,The α-diversity index of AM fungi decreased significantly,and the biomass of AM fungi also decreased significantly.3.Nitrogen deposition changed the composition of herbaceous plant communities and reduced their α-diversity.Nitrogen application changed the distribution of herbaceous plants in the understory.With the increase of nitrogen application rate,the diversity of herbaceous plants decreased significantly,and the biomass of fine roots also decreased significantly.The diversity of herbaceous plants was significantly positively correlated with the diversity and infection rate of AM fungi.Herbaceous plant fine root biomass and its diversity also showed a significant positive correlation.Plant diversity was significantly negatively correlated with soil total nitrogen and ammonium nitrogen,and significantly positively correlated with soil pH.In addition,the long-term nitrogen addition affects the diversity of AM fungi and herbaceous plants mainly through the changes of soil pH,available phosphorus and ammonium nitrogen.In summary,long-term application of different concentrations of nitrogen under the forest changed the soil pH,the distribution of N and P elements,the distribution of soil aggregates,and the content of glomycin in the soil,and reduced the diversity of AM fungi and understory herbaceous plants.The community composition of AM fungi was changed,the ways in which nitrogen deposition changed the diversity of AM fungi and herbaceous plants in forest ecosystems were explored,and the diversity reduction of AM fungi and herbaceous plants under the pressure of global climate change was verified.