The Interaction And Effect Of Two Arbuscular Mycorrhizal Fungi On The Growth Of Astragalus Sinicus L At Different PH Level

Arbuscular mycorrhiza fungi distribute widely in the environment.They exist in variouskinds of soil condition and establish closed relation ship with many different host plants.It was found that about 80% of the terrestrial plants have arbuscular mycorrhiza fungi,host plant can also affect the growth and development of AM fungi.Many factor, such as water content, pH, fertility, light and temperature,can obviouslyinfluence the symbiosis of plant and arbuscular mycorrhiza fungi,and produce differentinfection rate, spore-bearing rate and mycorrhizae effect. The objective of this study isfocus on the effect of two species of arbuscular mycorrhizal fungi, Glomus mosseae andGigaspora margarita to Astragalus sinicus biomass under the condition of the four pHlevel,ranging from acidic to neutral (4.3,5.1,5.Sand6.8), and the relation ship betweenthem.The infection rate (M%) was calculated by TB coloration (Trouvelot et al. 1986) with"MYCOCALC" software. Meanwhile, the enzyme activity of succinatedehydrogenase(SDH) and alkaline phosphatase(ALP) was tested according to tissuecoloration(Zhao et al. 1997) on different pH level. The result showed that there was anapparent relativity between plant biomass and the colonization rate and the enzymeactivity of AM fungi.The colonization rate was increased with the rising of pH valuewhen the plants were inoculated with Glomus mosseae alone or with mixed strains,butwhen the plants were inoculated with Gigaspora margarita alone,the colonization ratewas the highest at the level ofpH 5.8,and then decreased at 6.8.Also,the relation shipbetween infection rate and the external hyphae length was established.Based on the analysis of highly variable region(D1-D2 domain) in 25SrDNA sequence,the interaction of the two fungal species at different pH level was detected by nested PCRwith special primers gml and gigl designed for Glomus mosseae and Gigasporamargarita respectively. Nested PCR specifically amplified the DNA of corresponding AMfungi from AMF muti-infected roots. In mixed inoculnm experiment,the result shows thatAt lower pH level(4.3-5.1),most of roots were infected by Gigaspora margarita,andGlomus mosseae apparently decreased the colonization of Gigaspora margarita.At higherpH level(5.8-6.8),most of roots were infected by Glomus mosseae,and Gigasporamargarita effectively increased the colonization rate of Glomus mosseae. None of theroots were simultaneously infected by the two fungal species. The application of developed molecular probes couple with nested PCR technique may open the possibilityfor revealing the interactions between AM fungi.