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Has files: YesSubject: search.filters.subject.Mycorrhizas in agriculture

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    Dual mutualistic associations in sainfoin (Onobrychis viciifolia Scop.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Agronomy at Massey University
    (Massey University, 1982) Kon, Kee Fui
    Recent studies established that many legumes, when infected with the appropriate Rhizobium spp. and arbuscular fungi, nodulated better and exhibited greater dinitrogen fixation than plants infected with only the rhizobia. A similar study, therefore, was carried out in a glasshouse using sainfoin (Onobrychis viciifolia Scop.), a legume that is rapidly gaining recognition as a potential forage crop in New Zealand and other parts of the world. Pre-germinated seeds (cv. Fakir) were planted in sterilized soils and incubated with an effective Rhizobium spp. (strain NZP 5301), a mixture of endophytes (Gigaspora magarita Becker & Hall, Glomus fasciculata (Thax. sensu Gerd.) Gerdemann & Trappe and Glomus tenuis (Greenall) Hall), or both eht rhizobia and endophytes. The experiment also included a control, without any inoculation. Endophyte infection, nodulation and dinitrogen fixation, total nitrogen and phosphorus concentrations, and plant growth and development were determined on eleven sequential samplings over about twenty weeks, up to the stage of green inflorescence. Arbuscular mycorrhiza formation did not occur with the first endophyte inoculation, containing Gigaspora magarita Becker & Hall, even after 93 days of growth. This is probably because the inoculum used consisted of a low quantity of viable spores and mycelia. The second inoculation, containing the three endophyte species, produced only a low degree of infection between day 115 and 137, possibly because the extensive root lignification and relatively higher root phosphorus concentration (0.50%) restricted fungal invasion and establishment within the root cortex. Mycorrhiza formation did not increase phosphate uptake, improve nodulation and dinitrogen fixation, or increase plant growth. This is due probably to the already well-developed root systems that were efficiently exploiting the small soil volume within the bags. Rhizobia-inoculated plants produced more nodules, larger nodules and consequently, a greater nodule dry weight than the uninoculated plants. The nodules produced in the inoculated plants were red instead of green as in the uninoculated plants, and exhibited a greater dinitrogen fixation. As a result, these inoculated plants contained a higher concentration of shoot, root and nodule nitrogen, and a greater dry weight accumulation in the shoots and nodules. The shoot and nodule phosphorus concentrations, however, were lower in the rhizobia-inoculated than in the uninoculated plants due to the greater amount of shoot and nodule tissues which caused a dilution effect. These rhizobia effects on nodulation and dinitrogen fixation, nitrogen and phosphorus concentrations, and plant growth and development became more prominent with time. The relatively higher nodule phosphorus concentration when compared with the shoot and root phosphorus concentrations suggests that phosphorus was presumably required in large quantities by the dinitrogen-fixing system.
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    An analysis of the effects of field-soil disturbance treatments on arbuscular mycorrhizal fungi : a thesis presented in partial fulfilment of the requirements for the degree of Master of Sciences in Plant Biology, Massey University
    (Massey University, 2001) Graves, Donald Wayne
    In soil and root ecosystems the partitioning of carbon is ubiquitously affected by interactions with heterotrophic rhizosphere micro organisms, including the potentially mutually beneficial (+,+) arbuscular mycorrhizal (AM) fungi. However, the existence and sustainable management of AM fungi is threatened by prolonged and or intensive disturbances of soil. Therefore this study set out to explore the relationships between plants, soil fungi and soil disturbance treatments. A containerised bioassay of maize seedlings was used to assess root inhabitation of arbuscular mycorrhizal fungi from samples of Manawatu silt loam pasture field soils, methods were adapted from Brundrett et al (1996). Development of a rapid method to visualise the AM fungal inhabited maize seedling roots was enhanced by an alternative light source on an Olympus SZIII dissection microscope. A 100W-equivalent fluorescent light tube produced less heat, but provided approximately five-fold more illumination than the original 20W Olympus incandescent light bulb. It was found that propagation of maize seedlings during mid to late winter and greenhouse environments with relatively limited light day-length and irradiance levels may have resulted in 'parasitic' (+,-) soil-fungal interactions, or reduced growth of maize seedling plant biomass. Soil fungal parasitism of plant growth was attributed to mutual competition (-,-) for carbon photosynthate resources shared between soil fungi and plant host symbionts. In addition, a Venn-diagram model is proposed with three entities depicting fungal and plant population interactions that include mutual costs and benefits derived from bidirectional exchange of mineral and carbon nutrients as follows; mutualism and protocooperation (+,+); neutralism (0,0); and competition (-,-). Intersecting sets of these entities depict a three-way continuum of population interactions; parasitism or predation (+,-), and prey or host escape (-,+); amensalism (0,- or -,0); and commensalism (0,+ or +,0).