Microorganisms and their interactions in soil play a critical role in nutrient transformations and cycling, and in sustaining soil productivity. Arbuscular mycorrhizal fungi (AMF) are a keystone group of fungi influencing nutrient cycling. In turn, the activity and composition of microorganisms in soil are influenced by management practices such as the choice of crop species and fertilization. Long-term effects of cropping, manuring and mineral fertilization on the soil-plant system were defined in three selected agro-ecosystems of Canada. A greenhouse experiment was also conducted to define the involvement of AMF in organic residue decomposition and nitrogen (N) mineralization.<p> In the greenhouse experiment, pasteurized soil was inoculated or not with a strain of <i>Glomus claroideum, G. clarum</i> or <i>G. intraradices</i>. 15N-labelled organic residue in a nylon mesh was buried in the soil. The fate of residue-N was determined after 24 weeks. Arbuscular mycorrhizal fungal species enhanced mineralization of organic residue to different degrees. The highest recovery of mineralized N by plants (25%) occurred when inoculated with <i>G. clarum</i>. The AMF enhanced N-mineralization differentially leading to differential plant growth stimulation, differences in the C-to-N ratio of the decomposing organic residue, and in soil microbial community structure.<p> In a field trial conducted on a Brown Chernozemic soil at the Semiarid Prairies Agricultural Research Centre in Swift Current, SK, eight years of phosphorus (P) (0, 20 and 40 kg P2O5 ha-1) application to alfalfa monoculture and alfalfa-Russian wildrye (RWR) dual culture modified the soil microbial community structure. Low levels of phosphorus (0 and 20 kg P2O5 ha-1) fertilization in alfalfa-RWR dual culture increased the abundance of fungivorous nematodes and grazing of AMF hyphae thus increasing the carbon drain from plants and ultimately reducing plant biomass.<p> In a sub-humid region of Saskatchewan on a a Black Chernozem soil, mineral N (0, 20 or 40 kg N ha-1) was applied for 10 years to pea grown continuously or in rotation with wheat. Lower yields in continuous-pea were associated with reduced abundance of beneficial Gram positive bacteria and AMF, and an increase in uptake of plant available Fe to toxic levels. These differences in soil properties were related to root rot which increased with years in continuous-pea. The soil environment in the continuous-pea rotation further led to lower organic carbon inputs, and to reduced soil microbial biomass and soil enzyme activity indicating a negative impact on nutrient cycling.<p> In the south coastal region of Agassiz, British Columbia, dairy manure slurry (DMS) and ammonium nitrate (AN) had been applied on a Regosol at the same annual rate of mineral N (50 or 100 kg mineral N ha-1) for nine years to perennial tall fescue, followed by one year of stand renovation through reseeding without fertilization. The multi-year application of DMS improved soil organic C, soil organic N, light fraction of organic matter, microbial biomass and enzyme activity as compared to mineral fertilization but the DMS-related increase in soil yield potential was lost in the process of stand rejuvenation. Dairy manure slurry application based on the crop N requirement also increased soil phosphate indicating increased environmental hazard. In conclusion, long-term use of DMS in multi-cut tall fescue can increase soil quality parameters but can also increase the risk of eutrophication of water bodies.<p> Overall, data showed that higher levels of soil nutrients can select for certain bacteria while AMF and other bacteria are more abundant under low soil fertility. On the other hand, different soil microbial groups were associated with different soil enzyme activities. From this study, I succeded in proving my hypothesis that practice of fertilization and choice of crop influence soil microbial community structure which further affect soil functioning.

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains vii, 57 p. : ill. Vita. Includes abstract. Includes bibliographical references.

The aim of this PhD was to investigate major gaps in our understanding of how mycorrhizal fungi and aphids interact via their effects on plants, and how these interactions regulate emission of plant volatiles and consequently aphid and parasitoid host location. A series of experiments was designed using broad bean (Vicia faba L.), pea aphids (Acyrthosiphon pisum) and their parasitoid wasp, Aphidius ervi and mixed or single spore cultures of AM fungi as a model system. This PhD has determined that arbuscular mycorrhizal fungi are more important drivers of above-ground ecological interactions than ever considered before. They have key roles in specialist aphid host location and in influencing their development. The antagonistic effect of aphids on functioning of mycorrhizal association suggests that the interactions operate in both directions. However, if plants were supplied with phosphorus the aphids did not affect mycorrhizal colonisation suggesting that at sufficient phosphorus availability plants can tolerate the effect of aphids on mycorrhizal colonisation. This demonstrates how dynamic the multi-trophic systems are and that their outcomes are also influenced by soil nutrient availability, with implications for agricultural practices. This PhD has discovered that underground signals carried through common mycelial networks warn neighbouring plants of aphid attack. This signalling allows plants that receive the signal to initiate their defence system by changing their profiles of volatiles emissions and repel aphids and attract their parasitoids so that they may prevent the attack. Because the signal transfer is rapid it incurs the greatest fitness benefit for the receiving plant and potentially also for the donor of the signal and for the fungi. We now need to determine the wider ecosystem implications of this phenomenon, how the signalling is regulated in nature and in agroecosystems and what the fitness consequences are for each component organism.

published_or_final_version / Botany / Doctoral / Doctor of Philosophy

No description available.

Development and functioning of arbuscular mycorrhizal (AM) symbiosis in the soil-plant system are required in sustainable agriculture. AM development of maize genotypes and uptake of nutrients as influenced by soil P levels were studied. Several experiments were conducted both in the greenhouse and in the field. / In greenhouse trials, pasteurized substrates were inoculated with Glomus intraradices as mycorrhizal treatments. Mycorrhizal development varied widely among maize hybrids and inbreds. Leafy normal stature (LNS) had the highest root colonization and shoot:root ratio and was the most responsive to AM fungi. Mycorrhizal development was generally reduced at high soil P and micronutrient levels. The percentage of root colonization was correlated with the ratio of plant tissue N/P only when soil N level was intermediate. Mycorrhizal plants increased uptake of Zn and Cu only at low P and low micronutrient levels, but decreased Mn uptake at higher micronutrient level. / In field trials, soil fumigation was used to eliminate AM fungi in control plots. Again LNS was most responsive to indigenous AM fungi, closely followed by Non-leafy normal stature (NLNS). Mycorrhizae increased uptake of K, Ca and Mg only when these nutrients and available P were low in soil. Correlations between extraradicular hyphae and plant concentrations of K, Ca and Mg suggested that uptake of K was more dependent on extraradicular hyphae than uptake of Ca and Mg. Total P uptake was higher in plots where the AM symbiosis was not repressed, but soil available P was not always reduced. / There is potential for development of mycorrhiza efficient maize hybrids performing well under low input management in sustainable agriculture.

Bibliography: leaves 169-193. / xxi, 193 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study investigated whether both S. Calospora and Glomus sp. "City Beach" WUM 16 both increase the rate of transfer of phosphate (P) to the plant Allium porrum, and whether the addition of P to the soil has any effect on the uptake rates. The main experiment compared the fungi under two P levels in soils. It was found that in soil with no added P, S. calospora depressed plant growth in the early stages, but was increased in later harvests. G. sp. "City Beach" increased plant growth throughout. In soil with added P, both sets of plants produced growth depressions at early stages. The effect on growth due to mycorrhizal symbiosis was greater in plants grown in soil with no phosphate added. There were no significant differences between the two fungi with reflexes of P across the interfaces. There were however temporal differences. The isolate of S. calospora did promote a positive plant growth response in A. porrum and transfer P to the plant. Mycorrhizal arbuscules were examined and visualised using Laser Scanning Confocal Microscope and 3D reconstructions performed. This allowed the surface area and volume of the arbuscules to be quantified in order to investigate differences between the fungi. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2000?

Bibliography: leaves 106-132. / iv, 132 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This project investigated the role of VAM fungi in the growth and nutrition of Linum usitatissimum L. in agricultural soils in southern Australia. It had two general aims: (1) to examine the role of indigenous VAM fungi in the growth and nutrition of linseed in field soil collected near Clare, South Australia; and (2) to examine the effect of VAM fungi on the Zn nutrition of Linola. / Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 2001

Thesis (Ph.D.)--University of Adelaide, School of Earth and Environmental Sciences, Discipline of Soil and Land Systems, 2005? / "August, 2004" Title from t.p. on PDF file; viewed 29 June 2005. Includes bibliographical references. Also available in a print form.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "December 2007." Includes bibliographical references. Online version available on the World Wide Web.