Biodiversity Of Arbuscular Mycorrhizal Fungi In Some Areas Of North China And Their Effect On Plant Growth

Arbuscular mycorrhizal (AM) fungi are important soil microorganisms in agroecosystems by enhancing host plant survival and growth in adverse conditions such as soils with low nutrient availability or heavy metal contamination. Biodiversity exists among AM fungi and is influenced by numerous factors including soil properties and plant species. If AM fungi are to be used in sustainable agricultural systems it is necessary to study native AM fungi in the target areas and then select efficient isolates that can be applied as inocula in the field to improve crop growth. The objectives of this study were to investigate the germplasm of AM fungi, to understand the distribution pattern of AM fungi in different ecological conditions such as area, soil factor and host plant, to select isolates effective in nutrient acquisition by the host plant sweet potato, to test their effectiveness under field conditions, and to monitor AMF after their introduction into the field.In order to study AM fungal diversity, representative soil samples were collected from fields in which various crop plants were grown in Shandong and Hebei provinces, and from heavy metal-contaminated soil in Liaoning province. Isolation and purification of the mycorrhizal fungi led to the identification of 33 species in seven genera. Thirty-nine pure isolates and eighteen pure cultures were obtained, of which five pure cultures were registered in the European Bank of the Glomales (BEG). A germplasm stock was established for storage of the resources in the target area. The results from analysis of the ecological diversity in the field soils and polluted soil showed that the frequency of occurrence of the genus Glomus was highest and Acaulospora was the second most abundant genus. Spore density was affected by soil Olsen-P content and pH. Soil pollution index and Olsen-P content were more closely related to species diversity in polluted soil, while pH and Olsen-P content were more closely related to spore density. Moreover, AM species composition was also affected by host plant species in polluted soils.Pot experiments were conducted to select efficient mycorrhizal isolates in terms of P uptake and plant growth by sweet potato. Four isolates, SP4, SP5, BEG 167 and BEG 141. were selected from the 17 tested isolates. The effectiveness of the isolates was related to ecological attributes such as the number of propagules formed in the soil. Differences in effectiveness of AM fungi in promoting plant growth and nutrient uptake were also observed among genera, with higher effectiveness in Clomus followed by Acaulospora and Scutellospora.The metabolism activity and distribution pattern of AM fungi were studied in the field. The results showed that the tuber fresh weight was greatly increased with intraradical alkaline phosphatase (ALP) activity and extraradical hyphal density greatly improved. The hyphal density paralleling with ridge was much more higher than it in the non-inoculation treatment.A field experiment was carried out to test the effectiveness of the selected isolates with sweet potato as host plant. The experimental results showed that the yield and quality of the tubers were improved by inoculation with mycorrhizal fungi. The isolates BEG 168, GSP4 and BEG 141 increasedsweet potato tuber yield by 10%. Reducing sugar content and total carotenes were increased in isolates GSP4 and BEG 141 by mycorrhizal inoculation. The introduced AM fungi were found in roots of sweet potato in the inoculation treatment by monitoring of discriminating probes. The experiment results indicate great potential of applying mycorrhizal biotechnology in sustainable agriculture in the future.