Mycorrhizal Theses and Dissertations

| 2007 | 2006 | 2005 | 2004 | 2003 | 2002 | 2001 | 2000 |
| 1999 | 1998 | 1997 | 1996 | 1995 | 1994 | 1993 | 1992 | 1991 | 1990 |
| 1989 | 1988 | 1987 | 1986 | 1985 | 1984 | 1983 | 1982 | 1981 | 1980 |
| BEFORE 1980 |

2003 * * * * * * * * * * * * * * * * * * * * * * *

Author: Anabela Marisa Azul
Title: "Diversidade de fungos ectomicorrízicos em ecossistemas de montado"
Degree: PhD
Year: 2003
Language: Portuguese
E-Mail: amjrazul@ci.uc.pt

DAVID HAGERBERG: The Growth of External Ectomycorrhizal Mycelia in the Field in Relation to Host Nutrient Status and Local Addition of Mineral. PhD thesis, Microbial Ecology, Lund University, Sweden.

Author: Myrna F. Landim
Title: Brazilian Atlantic Rainforest Remnants and Mycorrhizal Symbiosis - Implications for Reforestation. A case study in Sergipe, Northeast Brazil
Degree: PhD
Year: 2003
Language: English
Institution: University of Bremen (UFT), Plant Physiology and Plant Anatomy, Leobener Strasse, D-28359 Bremen, Germany
Key-Words: Arbuscular Mycorrhiza, Ectomycorrhiza, Atlantic rainforest, Forest fragments, Reforestation, Sergipe, Brazil Supervisor: Heyser, W.
E-Mail: landim@ufs.br
Summary: This work presents results of several aspects of the ecology of two Brazilian Atlantic rainforest remnants. Both forests are situated in the Sergipe state of the Brazilian northeast region. The region is characterized by a marked rainfall seasonality, which is likely to affect soil nutrient dynamics and plant reproduction and recruitment. Sampling was therefore carried out in the two periods. One of the forest fragments (Crasto forest) was a coastal tableland forest on Red-Yellow Podzols, the other, a restinga forest (Caju forest) on quartziferous sands. Soils, as typical tropical soils, are moderately to strongly acidic, with relatively high Al levels and nutrient-poor. The Crasto site presented generally higher nutrient levels, maybe due to the higher clay content in its soils, but in both, nutrients were generally concentrated in the soil upper layers. Collections were also carried out in the adjacent region of each fragment, occupied by a coconut plantation in both sites. With some minor variation, these regions presented lower nutrient levels than the forest plots. Soil properties are, therefore, probable to hinder tree seedling establishment and, consequently, forest restoration in these areas. The mycorrhizal symbiosis is also equally important to plant growth, particularly during the seedling phase, and may have been similarly affected by disturbance. Aiming to investigate the potential of native mycorrhizal species on forest regeneration, the assessment of mycorrhizal symbiosis in roots of seedling and trees was performed as well as the analysis of the spatial distribution of inoculum (spores and roots). Arbuscular mycorrhizal fungi (AMF) was, like in all tropical ecosystems, dominant. AMF inoculum was not, contrary to the expectation, excluded from the plantation plots. In fact, spore species richness was higher than in the forest plots. Disturbance in these areas was therefore not enough to eliminate the occurrence of the mycorrhizal symbiosis. However, both sites differed in its response. In the Caju forest, roots in plantation sites presented higher colonization levels than in the Crasto site. Difference in soil properties and/or management practices may be responsible for these results and will be further examined. AMF spore species richness and root colonization levels were higher in the upper layers of the soil, similarly to the nutrient and root biomass. Disturbance that involve active removal of the top soil or increasing of soil erosion will therefore remove also the native AMF inoculum important for plant growth and survival, particularly under stressed conditions. Seedling recruitment was lower in the plantation than in forest plots. However, forest fringe plots presented also similarly low values. Seedling root mycorrhizal colonization was spatially uneven. Analysis of seedling roots from four different native tree species revealed a very variable picture of colonization type and intensity between species. An important finding was the high colonization levels of roots of some of these seedling species by dark septate endophyte (DSE), group of fungi supposed to have diverse phylogenetic origins and at present being tentatively placed in the Deuteromycotina, or Fungi Imperfecti. Both pathogenic and positive effects have been reported for plants in culture with these fungi, and it is not clear whether the analyzed seedlings benefit from them. As all the seedlings seemed to be healthy, without any noticeable signal of disease or nutrient deficiency, and as this root endophyte was also found in roots of some tree species analyzed, it is probable that these unexpected root partner may have a positive effect in enhancing plant growth and survival. This is an important issue for tree seedling recruitment and will be considered in subsequent studies. The analysis of native tree roots revealed also that ectomycorrhizal inoculum, although rare, is present in these forests, as one of the selected species, Cocoloba rosea (Polygonaceae), presented ectomycorrhizal roots. The family is already described in the literature as presenting ectomycorrhizal tropical species, suggesting an important taxonomic, more than biogeographical, component determining the distribution and occurrence of ectomycorrhizas in tropical regions. For recomposition of these tropical forests, however, arbuscular mycorrhizas are far more important. Contrary to some studies relating mycorrhizal colonization and host successional status, roots from pioneer species, Cecropia pachystachya and Vismia guianensis, were strongly colonized and will be subject of future investigations. Preliminary experiments intending to test the ability of native AMF inoculum in promoting seedling growth and survival were performed with a native legume tree species, Bowdichia virgilioides. These experiments aimed to compare native mixed inoculum from plantation and forest plots as well as pure inoculum (Glomus clarum) under different P levels or sources (KH2PO4 and phytate). The observed positive effects of AMF inoculation on plant growth, even with native mixed inoculum, suggests native inoculum can be successfully used on restoration of these deforested regions. Moreover, the high AMF colonization of the pioneer species, C. pachystachya and V. guianensis, should be managed to maximize the effects of inoculation of B. virgilioides seedlings in field conditions.

Author: Michelle Shawn Schroeder
Title: PHOSPHORUS AVAILABILITY AND PLANT DENSITY ALTER FACULTATIVELY MYCOTROPHIC PLANT SPECIES RESPONSES TO ARBUSCULAR MYCORRHIZAS
Degree: Ph.D.
Year: 2003
Language: English
Institution: University of Miami
Supervisor: David P. Janos
e-mail: michelle_schroeder@ncsu.edu
Abstract: Although phosphorus availability and plant density independently have been demonstrated to alter plant growth, little is understood regarding how these factors interact to alter plant responses to arbuscular mycorrhizas (AM). In this study, I examined the effects of AM, phosphorus availability, and density on growth responses of five crop species (Capsicum annuum, Coriandrum sativum, Cucurbita pepo, Lycopersicon esculentum, and Zea mays). I grew these facultatively mycotrophic species (capable of growth without AM in fertile soil) in pots using tropical soils low in available phosphorus. I also quantified root morphological and phosphorus uptake responses to AM, phosphorus fertilization, and intraspecific density for C. annuum, C. pepo, and Z. mays. Lastly, I examined AM effects on intra-and interspecific interactions among the latter three species with a complete-additive design experiment. Despite investigating unrelated host species and different suites of AM fungus species, I consistently found increased phosphorus and intraspecific density diminished plant responses to AM. Although AM increased specific root lengths and root branching of Z. mays and C. annuum, reduced Z. mays fine root diameters, and increased C. annuum and C. pepo shoot phosphorus concentrations, increased phosphorus and density diminished these effects. Specific results, however, depended on phosphorus availability and each plant species' ability to acquire phosphorus on its own. At high phosphorus, increased density diminished AM effects on plant growth, reducing AM benefit to C. annuum and L. esculentum and reducing AM detriment to C. sativum. In contrast, for a second C. annuum variety, increased density diminished AM growth benefits at low phosphorus. I attribute these density-dependent effects of AM to increased root density causing increased overlap of root and hypha phosphorus depletion zones, which may reduce phosphorus uptake benefits of AM at low phosphorus, but may enhance uptake of phosphorus by AM at high phosphorus. Lastly, I found AM reduced both intra- and interspecific competition when AM caused growth detriment to C. pepo and Z. mays. These results suggest that similar AM effects on plant species that recruit densely may be important determinants of plant competition with consequences for community composition and plant species diversity.