Diversity And Ecological Distribution Of Arbuscular Mycorrhizal Fungi In The Rhizosphere Of Artemisia Sphaerocephala

AM fungi, as a kind of the most common mycorrhizal fungi, widely exist in various ecological system, and can infect most plant roots, and form mutualistic symbiosis with them. The symbiosis can expand absorption range of roots by forming dense hyphal nets in rhizosphere soil, to promote plant growth and improve plant stress tolerance; In addition, the colonization of AM fungi can also promote the decomposition of the soil organic pollutants, increase the amount of soil aggregate, and then improve soil quality and structure. Dark septate endophytes (DSE) is another group of fungi settled in the host roots with unclear ecological position and function, that can also form mutualistic symbiosis. Artemisia sphaerocephala can easily form reciprocal organells with AM fungi for its developed root, thereby become the pioneer sand-fixation plant in desert habitat, and thus play an important role in preventing sand-fixation and promoting the sandy management.To elucidate the species diversity of AM fungi, the temporal and spatial distribution of AM fungi and DSE and their relationship with environmental factors associated with the common desert plant A. sphaerocephala, we sampled from three different sites in Inner Mongolia in April, July and October 2009, which are Yuan Shangdu, north of Hei Chengzi and Da Hexiang, respectively. Root samples were collected from four robust A. sphaerocephala, and soil samples were taken from the rhizosphere of A. sphaerocephala in three sites and divided into five depth intervals, 0-10 cm, 10-20 cm, 20-30 cm, 30-40 cm and 40-50 cm respectively. Results are as follows:An abundant species diversity of AM fungi was found from A. sphaerocephala in Inner Mongolia. 20 AM fungi taxa in three genera were isolated and identified, of which 70% belong to the genus Glomus, 20% to Acaulospora and 10% to Scutellospora. Among these 20 AM fungi taxa, G. dolichosporum and G. etunicatum were not found in Da Hexiang site, and Scu. calospora was not found in Yuan Shangdu site and in the soil samples of Hei Chengzi in April. In all the species, G. reticulatum and G. melanosporum were the dominant species in the rhizosphere of A. sphaerocephala in all the three sites, and G. aggregatum was the most common species. SEM showed that, surface grain characteristics of each AM fungi were different, that can be used as a kind of identification basis, and each AM fungi has its own ecological adaptability to the extreme environment.There were certain regularity of the species diversity on the spatio-temporal distribution of AM fungi. From the temporal perspective, AM fungi was with the lowest diversity in spring, and rise with the passage of time, achieve maximum in fall, and the overall trend showed April < July < October. From the spatial perspective, AM fungi was with the lowest diversity in Yuan Shangdu, and highest in Da Hexiang, and the overall trend showed Yuan Shangdu < Hei Chengzi < Da Hexiang. There were no significant correlation between species ichness, Shannon-Wiener index, evenness and soil factors.A. sphaerocephala can form functional symbiosis with AM fungi and produce Intermediate type mycorrhizas. Mean total root infection of AM fungi was 92.32%, mean spore density was 878.5 No.100g-1. Meanwhile, the root of A. sphaerocephala could still be infected by DSE, and the infection rate reached 62.31%.A certain law of the temporal distribution of AM fungi and DSE were found. No significant differences of mycorrhizal colonization were found in each months, while the minimum colonization of AM fungal and DSE were all appeared in spring. With the passage of time, spore density and AM fungal colonization picked in summer, and declined slightly in the autumn. While the DSE colonization increased gradually over time.The spatial distribution of AM fungi and DSE were regular. There were no significant differences of spore density, AM fungal colonization and DSE colonization among these three sites, but the maximum all appeared in Hei Chengzi, were 1143.3·100 g-1soil,95.59% and 96.60%, respectively; From vertical profile of soil, spore density and mycorrhizal colonization peaked at the 0~20cm soil layer, and significantly reduced with the increasing of soil profile depth.The colonization of AM fungi and DSE in the rhizosphere of A. sphaerocephala was closely related with the environmental factors. Spore density had a significantly positive correlation with soil pH, organic matter, available N, alkaline phosphatase and urease activity; and had a significantly negative correlation with soil layer. Total and hyphal colonization both had significantly negative correlations with acid phosphatase activity. Vesicular colonization had significantly positive effects on soil pH, and had significantly negative effects on acid phosphatase activity. Arbuscular colonization was positive correlated with soil pH, and was significant negative correlated with acid phosphatase activity. DSE colonization had a significantly negative correlation with acid phosphatase activity. Thus, the formation, distribution and activity of mycorrhizal were significantly affected by the ecological conditions and acted on the ecological conditions at the same time.