Arbuscular mycorrhizal fungi (AMF) provide numerous services to their plant symbionts. Understanding the effects of climate change on AMF, and the resulting plant responses, is a crucial factor in predicting ecosystem responses on a global scale. We used a manipulative climate change experiment embedded within a natural climate gradient in Oregon and Washington to examine how the effects of future climate change on AMF-plant symbioses are mediated by soil water availability, soil nutrient availability, and vegetation dynamics. Using structural equation modeling, we found that the direct effect of increasing temperatures was to decrease AMF colonization. Indirect effects of temperature, mediated through other variables, canceled each other out. However, future shifts in these relationships could either exacerbate or mitigate the negative direct effect of temperature. As ecosystems in Mediterranean climates experience more intense droughts and heavier rains, decreases in AMF colonization could have substantial consequences for plant communities and ecosystem function.

Arbuscular mycorrhizal (AM) fungi are important symbionts to most of the terrestrial plants. Recent genome sequencing projects revealed that many AM fungi have repetitive genetic elements in their genomes and among these repetitive genetic elements, cut-and-paste DNA transposable elements were very prevalent. For example, in Rhizophagus irregularis, up to 21% of the genome assembly content was associated with cut-and-paste DNA transposable elements. In Diversispora epigaea, up to 23% of the genome content can also be attributed to cut-and-paste DNA transposable elements. While cut-and-paste DNA transposable elements are very abundant in AM fungi, detailed studies on these repetitive elements have been lacking. In this study, we revealed the diversity of cut-and-paste DNA transposable elements in Claroideoglomus claroideum and identified many potentially autonomous transposable elements in the genome assembly of C. claroideum. The evolutionary relationship between the DNA transposons we identified and the established sequences in public databases were also investigated.

The present study was aimed to find out if there is any symbioses between C.australe roots and mycorrhizal fungi. This research also aimed to investigate the effect of Arbuscular mycorrhizal fungi on the growth of C.australe and the yield of alkaloid castanospermine. The rhizosphere soil and roots of C.australe from various sites in Sydney were collected. Roots were stained with vital and non-vital stains for assessment of mycorrhizal infection. The result indicated that AM fungi symbiotic associations with the roots of C.australe, producing arbuscules and vesicles in the root cortices. By wet sieving and decanting of rhizosphere soil, spores and sporocarps of AM fungi, were recovered. The spores mainly belonged to the genus Glomus. A correlation study was conducted to determine the relationship between the AM infection percentage in the roots and the Castanospermine amount in the leaves and seeds of the field grown trees. The results showed that there is a positive relationship between the castanospermine amount in the seeds and AM infection percentages in the roots. The effect of phosphorus on the yield of castanospermine was also investigated. The results indicated that phosphorus do enhance castanospermine at certain levels, but a further increase in phosphorus application resulted in reduced AM infection. It was found that AM has a great effect on the growth and production of C.australe and biosynthesis of castanospermine. / Master of Science

The present study was firstly aimed at producing the AM fungal inocula by using soil-based and soil-less culture techniques, including the in-vitro axenic technique, and secondly to assess the infectivity and effectiveness of the inocula so produced in glasshouse and field conditions. Indigenous AM fungi from 5 different sites of New South Wales were successfully propagated and multiplied using the pot-culture and atomizing disc aeroponic culture techniques, and their infectivity was measured using the MPN bioassay method. The coarse and fine sand mix was proven to be very effective for the production of AM fungal inocula. The findings indicated that aeroponic culture technique is far superior to that of conventional pot-culture technique, and could possibly substitute the most commonly used pot-culture technique of AM fungal inoculum production. The ultra-sonic nebulizer technology could possibly be an alternative to conventional aeroponic systems for producing AM fungal isolates in commercial quantities. The introduction of the sheared-root inoculum of Glomus intraradices, produced by the ultra-sonic nebulizer technique, into agricultural soils can substantially reduce the intake of P-fertilizers as much as 50% of the recommended level. The study also indicated that soil phosphorus is a critical factor in limiting mycorrhizal colonization, possibly limiting mycorrhizal responses.The research suggests that various commercially produced single or 'cocktail' inocula may work on mycorrhiza dependent plants in soils where the indigenous AM flora is either not abundant and/or efficient. Furthermore, ecophysiology of the same AM species have different effects on plant growth. / Doctor of Philosophy (PhD)

Graduation date: 1999

Thesis (doctoral)--Technische Universität Darmstadt, 2005. / Title from PDF title page (viewed on Apr. 25, 2007). Includes bibliographical references (p. 95-115).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on Feb. 6, 2007). PDF text: iii, 121 p. : ill. UMI publication number: AAT 3216344. Includes bibliographical references. Also available in microfilm and microfiche format.

High bicarbonate (HCO3-) content and associated high pH of irrigation water is detrimental to plant growth. Sustain ableagricultural/horticultural production will increasingly have to rely on economically feasible and environmentally sound solutions to the problems associated with high levels of HCO3- in irrigation water. The ability of a mixed Glomus Tulasne & Tulasne species inoculum of arbuscular mycorrhizal fungi (AMF), Glomus ZAC-19 (containing Glomus albidum Walker & Rhodes, Glomus claroideum Schenck & Smith, and Glomus diaphanum Morton & Walker), to enhance plant tolerance to HCO3- was tested on the growth and nutrient uptake of Rosa multiflora Thunb. ex J. Murr. cv. Burr (rose). Arbuscular mycorrhizal colonized and non-inoculated (non-AMF) R. multiflora cv. Burr were treated with 0, 2.5, 5, and 10 mM HCO3-. Increasing HCO3- concentration and associated high pH reduced R. multiflora cv. Burr growth, nutrient uptake, and acid phosphatase activity (ACP), while increasing alkaline phosphatase activity (ALP). Inoculation with AMF enhanced plant tolerance to HCO3- as indicated by greater growth, nutrient uptake, leaf chlorophyll content, higher mycorrhizal inoculation effect (MIE), lower root iron reductase activity, and generally lower soluble and wall-bound ALP activity. While AMF colonization (arbuscules, vesicles, and hyphae formation) was reduced by increasing HCO3- concentration, colonization still occurred at high HCO3- concentration. At 2.5 mM HCO3-, AMF plant growth was comparable to plants at 0 mM HCO3-, further indicating the beneficial effect of AMF for alleviation of HCO3- plant stress.

High bicarbonate (HCO3-) content and associated high pH of irrigation water is detrimental to plant growth. Sustain ableagricultural/horticultural production will increasingly have to rely on economically feasible and environmentally sound solutions to the problems associated with high levels of HCO3- in irrigation water. The ability of a mixed Glomus Tulasne & Tulasne species inoculum of arbuscular mycorrhizal fungi (AMF), Glomus ZAC-19 (containing Glomus albidum Walker & Rhodes, Glomus claroideum Schenck & Smith, and Glomus diaphanum Morton & Walker), to enhance plant tolerance to HCO3- was tested on the growth and nutrient uptake of Rosa multiflora Thunb. ex J. Murr. cv. Burr (rose). Arbuscular mycorrhizal colonized and non-inoculated (non-AMF) R. multiflora cv. Burr were treated with 0, 2.5, 5, and 10 mM HCO3-. Increasing HCO3- concentration and associated high pH reduced R. multiflora cv. Burr growth, nutrient uptake, and acid phosphatase activity (ACP), while increasing alkaline phosphatase activity (ALP). Inoculation with AMF enhanced plant tolerance to HCO3- as indicated by greater growth, nutrient uptake, leaf chlorophyll content, higher mycorrhizal inoculation effect (MIE), lower root iron reductase activity, and generally lower soluble and wall-bound ALP activity. While AMF colonization (arbuscules, vesicles, and hyphae formation) was reduced by increasing HCO3- concentration, colonization still occurred at high HCO3- concentration. At 2.5 mM HCO3-, AMF plant growth was comparable to plants at 0 mM HCO3-, further indicating the beneficial effect of AMF for alleviation of HCO3- plant stress.

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