Abstract: Arbuscular mycorrhizal fungi(AMF) are ubiquitous fungi distributed widely in soil ecosystems. It has been showed that AMF play an important role in improving soil nutrition and enhancing stress resistance. In order to reasonably use AMF resources, two types of soil such as lime soil (LS) and acid soil (AS) sampling from Karst area were used as potted matrix, and two AMF including Glomus mosseae (G.m) and Glomus etunicatum (G.e) were employed to be investigated respectively. The influence mechanism of AMF on plant biomass and soil enzyme activities in rhizosphere of Fortunella margarita Seedlings of Karst area were also discussed. The results show that, comparsion to the no AMF treatment (-AM),the colonization rate of root system of Fortunella margarita seedlings inoculated with either G.e and G.m increased significantly. No matter in either type soil, the colonization frequency of root system (F), colonization rate of root segment (m) and vesicle abundance of root segment (v) of Fortunella margarita inoculated with G.e are significant higher than those with G.m. The F, m, v of Fortunella margarita seedlings with G.e in AS had the maximum level,and those with G.m in LS were second. In addition, compared with the (-AM) treatment, rhizospheric soil enzyme activities of Fortunella margarita seedlings including protease, urease,invertase and phosphatase, along with soil organic carbon (SOC) content, soil organic matter (SOM) fraction and plant biomass rose significantly. Among them, the trends of activities of protease and urease were listed: (LS+G.e)>(LS+G.m)>(AS+G.e)>(AS+G.m), those of invertase and phosphatase were: (AS+G.e)>(AS+G.m)>(LS+G.e)>(LS+G.m), with a very significant level of all (P≤0.05). Moreover, the increasement of protease and urease activity received the first and second place, respectively, the third was that of invertase, and that of phosphatase was at a minimum level. As to rhizospheric SOC content and SOM fraction of Fortunella margarita seedlings, the change trends were shown below:(AS+G.e)>(LS+G.e)>(LS+G.m)>(AS+G.m). Regardless of what type of soil, contents of SOC and SOM of Fortunella margarita inoculated with G.e treatment were significant higher than those with G.m, similar to the changing trend of the colonization rate. The dry matter accumulation (biomass)of Fortunella margarita seedlings also showed a tendency to promote growth corresponding to the AM fungi inoculation. It is concluded that AM fungal symbiont can stimulate the activities of rhizospheric soil enzyme, facilitate the conversion of available nutrients such as N, P, K and fertility in AS and LS, and promoted plant growth in the end. G.e is the screened potential dominant species which possesses a better efficiency symbiosis with Fortunella margarita seedlings no matter growing in AS and LS and have great application potential in overcoming soil infertility and poor crop output problems of Karst area.

Key words: karst area, Fortunella margarita, arbuscular mycorrhizal fungi, soil enzyme activities, growth