| Grassland covers a vast area in China,carrying the development of traditional animal husbandry and playing a very important role.At the same time,grassland ecosystems are sensitive and easily disturbed by global changes and human activities.With the advancement of industrialization,global nitrogen deposition has become increasingly serious,causing serious impacts on grassland ecosystems.Mowing is one of the important methods of grassland management in China,which can alleviate the negative impact of nitrogen deposition on the diversity of aboveground and underground communities to a certain extent.Arbuscular mycorrhizal(AM)fungi play an important role in the ecosystem as a bridge connecting aboveground and underground communities.occupying two ecological niches.Studying the effects of nitrogen deposition and mowing on AM fungal community composition and diversity helps to assess the impact of global change and human activities on ecosystems.However,few studies have explored AM fungal communities in soil and roots simultaneously.Therefore,this study relied on Erguna Forest-Steppe Ecotone Ecosystem Research Station.Two nitrogen compounds(ammonium nitrate and urea),four nitrogen additions(2,5,10,20 g N m-2 yr-1),and two methods of grassland management(mowing and unmowing)were selected.Through high-throughput sequencing technology,combined with plant community investigation and soil properties measurement,the effects mechanisms of nitrogen deposition and mowing on AM fungal community composition and diversity in soil and plant mixed root system were investigated.The main results of and conclusions are as follows:1.AM fungal communities in soil and roots responded differently to nitrogen deposition.Nitrogen compound types had no significant effect on the composition and structure of AM fungal community in soil;while nitrogen addition rates significantly affected the community composition and diversity of AM fungal in soil.The a diversity of AM fungal community in soil decreased with increasing nitrogen addition,and its community structure changed under high nitrogen addition rates(10,20 g N m-2 yr-1).Nitrogen addition rates had no significant effect on the composition and diversity of AM fungal communities in roots.Nitrogen addition affected AM fungal community composition and diversity by affecting soil pH and inorganic nitrogen content,while plant community composition had no significant effect on AM fungal community composition.Long-term nitrogen fertilization may have reduced the plant’s dependence on AM fungi.There were differences in soil and roots AM fungal community composition and diversity.The α-diversity of the soil AM fungal community was significantly higher than that of the roots,and its community composition was dominated by Glomeraceae,Diversisporaceae and Paraglomeraceae,while Glomusaceae accounted for the vast majority of the root AM fungal community.2.Mowing mitigated the negative effects of nitrogen addition on plant community diversity but not did mitigate the negative effects on AM fungal communities.Nitrogen addition promoted the growth of nitrogen-loving plants and caused shading of low plants,thereby reducing the a diversity of plant communities.Mowing alleviated the light limitation of low plants by altering the height of plants and mitigated the negative effects of nitrogen addition on plant community diversity.Nitrogen addition reduced the diversity of AM fungal communities in soil by affecting soil pH and inorganic nitrogen content.However,mowing did not alleviate the negative effect of nitrogen addition on AM fungal community diversity in soil,probably because mowing did not change soil pH and inorganic nitrogen content.Under nitrogen addition and mowing,the ecological process of AM fungal community assembly did not change,and environmental filtration was a major ecological process driving AM fungal community assembly.In this thesis,nitrogen deposition was simulated from the perspectives of nitrogen compound forms and nitrogen addition rates to discuss the response of AM fungal community composition and diversity in temperate meadow steppe to nitrogen deposition and mowing.It enriches the research on the impact of mowing on the underground community of grassland ecosystem under global change,and reveals the important practical significance of mowing in grassland management. |
