Primary Investigation On Diversity Of Arbuscular Mycorrhizal Fungi Under Different Grazing Pressures

Arbuscular mycorrhizal, which is a symbiosis formed by plants and Arbuscular mycorrhizal fungi (AM fungi), is an important part of ecosystem. The AM fungi distributes widely in grassland system, and affects the growth, physiology and ecology of host plants, as well as alters the competition relationship between different kinds of plants and circulation of ecosystem. Actually, the composition and structure of plant communities and the plant diversity are influenced by the species richness of AM fungi directly, while plant productivity and community stability are greatly influenced by its diversities. Grazing is an important management method of grassland ecosystem, which can directly affect plant diversity and the physical and chemical properties of soil. It can also indirectly affect the composition of micro-organisms including the diversity of AM fungi in soil, and vice versa.In our experiment, the morphological methods were used to study the changes of AM fungi species diversity under different grazing pressures on the rangeland in the Songnen Plains which is analyzed based on the characteristic of plant community and the chemical&physical properties of soil. Results not only offer experiment evidence for analyzing the ecological mechanism of the AM fungi diversity responding norm to different grazing pressures, but also, to some extent, can provide a theoretical basis and technical guide for the reconstruction and restoration of the damaged grassland ecosystem, as well as further exploration and understanding the functions of AM fungi diversity.Thirteen species of AM fungi were identified, which belong to the following four categories, Glomus, Acaulospora, Scutellospora and Paraglomus in grazed plots. The plots with middle grazing pressure is most abundant with ten AM fungi, followed by the light grazing pressure (8 species) and the extreme heavy grazing pressure (4 species). The Glomus is the most, followed by Acaulospor. G. AMbisporum, G. mosseae and G. fasiculatum were the three species of spores, which existed in all grazed plots.AM fungi spore density and colonization rate varied among different grazing pressures. Under the light grazing pressure, the spores density and colonization rate were highest compared to other grazed area. The spore density and the colonization rate are lowest under heavy and extreme heavy grazing pressure respectively. The un-grazed plots had lower AM fungi spore density than grazed plots, but had higher colonization rate than heavy and extreme heavy grazed plots.The diversity index of AM fungi varied with the grazing pressures. The highest value appeared in the plots with middle grazing pressure and the lowest is in the plots with extremely grazing pressure. Based on the investigations of plant communities and the physical and chemical properties of soil, the relationship between AM fungi diversity index and plant community characteristics, dominant plant and the physical and chemical properties of soil were further analyzed in our experiment. Results showed that: (1) The diversity of AM fungi decreased gradually with the increase of the plant diversity, and increased with the plant community production, the density and important value of dominant plant. (2) The stability of AM fungi community (indicated by evenness index of AM fungi) increased with the density of plant community, the aboveground and underground production, the important value and density of dominant plant. (3) The diversity of AM fungi increased correspondingly with the soil water capacity, pH and conductivity.So, we can conclude that AM fungi species diversity under different grazing pressures is different. Its variation is opposite with the plant diversity, but the same with the production of host plants, the water capacity, pH and conductivity of soil which revealed the relationship between the diversity of AM fungi and the different grazing pressures.