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1998 * * * * * * * * * * * * * * * * * * * * * * *
ACCESSION NO.: AAG9813957
TITLE: THE ROLE OF MYCORRHIZAE IN SOYBEAN GROWTH IN P-DEFICIENT
SOIL IN THE HUMID TROPICS (GLYCINE MAX, PHOSPHORUS
DEFICIENT SOIL)
AUTHOR: ABDELGADIR, ABDELAZIZ HAMID
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: CORNELL UNIVERSITY; 0058
SOURCE: DAI, VOL. 58-11B, Page 5726, 00310 Pages
DESCRIPTORS: AGRICULTURE, SOIL SCIENCE; AGRICULTURE, AGRONOMY;
BIOLOGY, MICROBIOLOGY
ABSTRACT: Studies of four hundred and sixty-five soybean (Glycine
max (L.) Merr.) varieties from different parts of the
world were conducted to determine their ability to grow
in P-deficient soils and to determine the effect of
vesicular-arbuscular (VA) mycorrhizal fungi on the
ability of soybeans to grow in such P-deficient soils in
the humid tropics.
A field experiment was conducted to investigate the
effect of addition of 0 and 60 kg fertilizer P/ha on
soybeans. The results showed that soybean varieties
differed markedly in their response to P, the time of
response to P, grain yield potential, nodulation,
mycorrhizal colonization, P absorption, and N$sb2$
fixation. Phosphorus addition increased the grain yield
of some soybean varieties by $ge$200%, caused a decline
in grain yield of $ge$40% in other varieties, and had no
effect on grain yield in other soybean varieties. The
addition of P fertilizer consistently reduced
mycorrhizal infection in the twenty-four soybean
varieties tested. The results show that soybean
varieties can be obtained that produce reasonably high
yields in P-poor soils without P fertilizer.
The symbiosis of twelve different VA mycorrhizal fungi
with two soybean varieties was also investigated. The
results indicated that VA mycorrhizal fungi differed in
their infectivity as well as in their effects on plant
growth. Depending on plant variety, the fungi were
symbiotic, parasitic or had no effect on plant growth,
suggesting the importance of evaluating the
compatibility of VA mycorrhizal fungus and plant host.
Studies were conducted of the effect of spore densities
of mycorrhizal fungi, interactions between VA
mycorrhizal fungi and Bradyrhizobium strains, and fungal
inoculation methods on root colonization by the fungi
and soybean growth. Significant differences in root
colonization or plant growth responses among spore
densities were not observed. Three different
Bradyrhizobium strains had similar effects on root
colonization by two VA mycorrhizal fungi tested.
Measurements of plant fresh weight revealed synergistic,
antagonistic and no interactions between Bradyrhizobium
strains and Glomus species. Placing spores of
mycorrhizal fungi under the seeds gave better plant
growth, nodulation and root colonization than mixing
spores in the soil. The effect of spore-placement
methods depended on Bradyrhizobium strain and
mycorrhizal species. Phosphorus and N contents of
soybean variety V295 were consistently improved by VA
mycorrhizal inoculation in P-deficient soils.
ACCESSION NO.: AAG9836949
TITLE: ECOLOGICAL INTERACTIONS IN FOREST RESTORATION IN LOWER
MONTANE ECUADOR (DEFORESTATION, SETARIA SPHACELATA,
PHOSPHORUS, MYCORRHIZAL FUNGI)
AUTHOR: ECKERT, GREGORY ERIC
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: UNIVERSITY OF GEORGIA; 0077
ADVISER: Director: C. RONALD CARROLL
SOURCE: DAI, VOL. 59-06B, Page 2543, 00149 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY; AGRICULTURE, SOIL SCIENCE;
AGRICULTURE, FORESTRY AND WILDLIFE
ABSTRACT: This dissertation describes findings related to forested
ecosystems in the northern Andean region. Deforestation
is widespread here, threatening the biodiversity of
forests there, particularly in mid-elevation zones with
high rates of diversity and endemism. The mycorrhizal
symbiosis was studied along a vegetation successional
gradient, including pastures of Setaria sphacelata,
which has been adopted by farmers because of ease of
management. Trends were found among means for total and
arbuscular infection in the dry season with greater
infection in roots of more complex (woody) vegetation
patches. Proportion of arbuscules to total infection was
much lower in low diversity Setaria sphacelata patches.
Soil phosphorus fractions, pH and phosphatase activity
also were evaluated. Resin P and bicarbonate inorganic P
extracts were low ($<$10 $mu$g P g$sp{-1}$ soil) but
did not exhibit any successional or land-use trends.
Phosphatase activity was similar to that found in other
Andic soils, but did not have any relationships with any
of the labile P fractions. Phosphorus characteristics
were not correlated to field root infection. Findings
suggest that low mycorrhizal activity and fungal
speciation in widely used Setaria pastures may be
limiting to alternative land uses.
Setaria slows successional processes once abandoned.
Studies of barriers to establishing trees in Setaria
indicated that shading limits the density of the Setaria
root mat, and allows for the establishment of several
forest species. When Setaria is cleared, and forest
litter is applied to the area, transplanted trees grow
well, but do not outgrow the Setaria regrowth. Repeated
control of the grass is necessary until transplants grow
above the potential height of Setaria (ca. 2 m.). Forest
restoration in Setaria should be feasible, but will
require a mix of active control and plantings to
facilitate natural processes of ecosystem
reorganization.
Restoration efforts in Ecuador must address issues of
local livelihood for long-term sustainability. Methods
aimed to elicit common, but not clearly demonstrated or
articulated actions and knowledge were used in
interactions between ecological researchers and local
community members. Methods included the use of key
informants, open-ended interviews, resource maps,
timelines, and association studies. Local participation
aids restorationists in species identification and
interactions as well as successional dynamics.
Participants also provide important perspectives to land
management and other economic issues, such as forestry
and forest product potential for buffer zone management
surrounding protected areas.
ACCESSION NO.: AAG9833776
TITLE: ECOLOGY OF ARBUSCULAR MYCORRHIZAS IN TALLGRASS PRAIRIE
(SYMBIOSIS)
AUTHOR: EOM, AHN-HEUM
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: KANSAS STATE UNIVERSITY; 0100
ADVISER: Major Professor: DAVID C. HARTNETT
SOURCE: DAI, VOL. 59-05B, Page 1978, 00130 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY; BIOLOGY, BOTANY
ABSTRACT: Arbuscular mycorrhizal (AM) symbiosis in tallgrass
prairie can be influenced by biotic and abiotic
environmental factors and interactions with both
belowground and aboveground processes. This study
examined the effects of environmental factors, prairie
management practices, and host plant species on
mycorrhizal symbiosis and species composition of AM
fungi. Tallgrass prairie sites subjected to ten years of
annual burning, mowing, fertilization (nitrogen or
phosphorus) were studied. Spring burning significantly
reduced fungal species diversity, while increasing spore
abundance. Burning and mowing had no significant effects
on fungal colonization of roots or extraradical
mycorrhizal hyphae (EMH). However, nitrogen
fertilization significantly increased root colonization
and EMH, and phosphorus amendment decreased EMH. There
was no significant effect of fertilizer amendment on
spore abundance, fungal species diversity or richness,
but nitrogen and phosphorus fertilization decreased
fungal species evenness.
To examine the effect of grazing, rhizosphere samples
were taken over a 2-year period in sites grazed for
several years by cattle at varying intensities and
inside and outside permanent 25-m$sp2$ exclosures. In
both years, moderate and intense grazing increased
mycorrhizal root colonization, and EMH was significantly
increased with intense grazing in 1995. AM fungal
species responded differently and individually to
grazing intensity and topography. Fungal species
diversity significantly decreased with both moderate and
intense grazing in both years and fungal species
richness was significantly higher on loamy uplands than
on rocky slopes.
To assess the influence of plant species on AM fungal
communities, the effects of five different tallgrass
prairie host plant species on AM fungal communities were
examined. Spore abundances and species composition of
fungal communities of soil samples collected from
tallgrass prairie were significantly influenced by plant
species. Results from sorghum trap cultures using soil
collected under different plant species showed
significant differences in AM fungal sporulations among
plant species. A greenhouse study showed that AM fungal
species composition grown in similar tallgrass prairie
soil were significantly different beneath each plant
species. These results indicate that AM fungi respond
differently to the host plant species and the different
host plant species may play an important role in the
maintenance of species composition and diversity in AM
fungal communities.
Title: Ecological Significance of Arbuscular Mycorrhizal Fungus-Plant Symbiosis in Saline Environment
Author: Gu Feng
Degree: PhD
Year: 1998
Institution: Plant nutrition department, College of Resources and Environmental Sciences, China Agricultural University, Beijing 100094
Advisor: Prof. Shengxiu Li, Prof. Xiaolin Li and Prof. Fusuo Zhang
Abstract: The arbuscular mycorrhizal fungus-plant association widely exists in nature. Although the symbiosis associate has been found in saline soil many years ago, the ecological significance of fungus-plant association is still unclear. In this study five plant species (soybean, corn, melon, cotton and bromus) and four arbuscular mycorrhizal fungal isolates (Glomus sp.) were used to investigate the effect of arbuscular mycorrhizal fungi on saline tolerance of plants and its mechanisms, the influence of saline stress on mycorrhiza formation under control conditions. The result and conclusions obtained are as follows:
1. AM fungus increased the saline tolerance of plant.
1.1 The biomass of plants were increased by 40%-70% in soybean, 10%-60% in bromus, 7%-60% in cotton and 10%-100% in maize respectively, when AM fungi were inoculated.
1.2 The effect of AM fungi on enhancing plant saline tolerance relied on some factors such as available phosphorus and salinity contents in soil, mycorrhizal dependency of plant, affinity of plant to fungus.
2.The mechanisms by which AM fungi alleviating saline stress are:
Firstly, AM fungi improved phosphorus status of plants.
Secondly, AM fungi colonization improved osmotic regulation in plant root .
Thirdly, AM fungi improved mineral elements composition by decreasing the relative concentration of sodium and chloride in plant.
And finally, the effect of AM fungus enhancing saline tolerance of plant is not an obligatory responsible for saline stress. It is determined by the characteristics of the symbiosis and the bio-characteristics of AM fungus.
3 Salinity affected the relationship between fungus and host.
3.1 Salinity restricted mycorrhiza formation. Mycorrhizal colonization was decreased with increasing of salt content in soil .
3.2 Salinity strengthened symbiotic association between host and fungus. Mycorrhizal dependency of plants were increased with salinity level increasing, which implied that the fungus-host association plays an important role for plant survival and growth in saline environment.
Key words: Saline environment, Arbuscular mycorrhizal fungus, Plant saline tolerance, Ecological significance
ACKNOWLEDEGMENT: We are greatly thank for the financial support by the Natural Science Foundation of China (Project 49961005).
ACCESSION NO.: AAG9902087
TITLE: ECOSYSTEM PERSPECTIVES ON CARBON AND NUTRIENT CYCLING
BELOW-GROUND (ANNUAL GRASSLAND, BISHOP PINE FOREST,
ALASKAN TUNDRA)
AUTHOR: GROGAN, PAUL
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: UNIVERSITY OF CALIFORNIA, BERKELEY; 0028
ADVISER: Chair: F. STUART CHAPIN, III
SOURCE: DAI, VOL. 59-08B, Page 3845, 00068 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY; BIOGEOCHEMISTRY
ABSTRACT: Primary production in most terrestrial ecosystems is
limited by below-ground resource availability. In this
dissertation, I describe studies that focus on
biological, chemical and physical influences regulating
carbon and nutrient transformations below-ground in
three different ecosystems.
In a Californian annual grassland community, the
influence of arbuscular mycorrhizal associations on
plant nutrient acquisition was investigated using
factorial combinations of nitrogen (N), phosphorus (P)
and benomyl fungicide. Plant production in control plots
was N-limited. However, production in plots treated with
fungicide was limited by both N and P supply. These
results suggest that effective P acquisition by
arbuscular mycorrhizae contributes to the strong N-
limitation of production observed in many terrestrial
ecosystems.
In a recently burned Californian Bishop Pine (P.
muricata) forest, the influence of surface ash on soil,
microbial and plant N pools was examined. Primary
production and ecosystem N retention were significantly
enhanced by the presence of ash in the first growing
season after fire. Analyses of ash samples indicated
that production was stimulated by direct ash N inputs to
soils and indirect physico-chemical effects on soil N
availability to plants. Comparisons of isotopic
$rmsp{15}N$ natural abundance values in burned and
mature P. muricata forest stands indicate that
fractionation of plant N sources increases as surface
organic layers develop after fire. This study suggests
that post-fire dispersal of ash by wind and rain can
result in marked heterogeneity in soil N availability
and may be an important mechanism contributing to
vegetation patchiness in fire-prone ecosystems.
In arctic Alaskan tundra, the impact of season on
climate and vegetation influences over CO$sb2$ release
from below-ground was assessed. Climate had strong
effects on CO$sb2$ efflux from below-ground in both
seasons, whereas differences in vegetation-type had
greatest effect in summer. A major finding from this
study is that below-ground CO$sb2$ release in winter
will be sensitive to the increases in temperature and
precipitation predicted by General Circulation Models.
These results demonstrate that seasonality is a critical
factor controlling regional patterns of below-ground
CO$sb2$ release and modulating feedbacks from arctic
ecosystems to global warming.
TITLE: EFFECTS OF ARBUSCULAR MYCORRHIZAL FUNGUS ON PHOTOSYNTHESIS OF PLANTAGO LANCEOLATA AT INCREASING LEVELS OF PHOSPHORUS
SUPPLY.
AUTHOR: ISTVÁN, PARÁDI
DEGREE: M.Sc.
YEAR: 1998
INSTITUTION: DEPARTMENT OF PLANT PHYSIOLOGY, EÖTVÖS LORÁND UNIVERSITY OF SCIENCES, MÚZEUM KRT. 4/A, H-1088 BUDAPEST,
HUNGARY. Email: para@ludens.elte.hu.
ADVISER: ZOLTÁN BRATEK, FERENC LÁNG
DESCRIPTORS: BIOLOGY, PLANT PHYSIOLOGY
ASTRACT: Influences of arbuscular mycorrhizal symbiosis and phosphorus supply on growth and photosynthetic parameters of
Plantago lanceolata were studied in a greenhouse pot experiment. Plants were grown for three months on a mixture of
c-irradiated loam and sand. Phosphorus was provided initially as 33, 196 and 1176 ppm KH2PO4 per pot. No extra phosphorus
was added to the control pots. Inoculum of Glomus fasciculatum (BEG 53) was used. Chlorophyll content, in vivo 14CO2
fixation, and chlorophyll fluorescence kinetics were measured. While the growth parameter values of nonmycorrhizal (NAM)
plants correlated with the phosphorus content, the amount of phosphorus had only a limited effect on the same parameters of
the mycorrhizal (AM) plants. At low phosphorus levels (0-33 ppm), the fresh and dry weights of the NAM plants were lower
compared to the AM ones, however, at high levels (196-1176 ppm), the opposite tendencies were observed. Mycorrhiza
formation increased the yield of CO2 fixation calculated either to unit leaf weight, unit leaf area or chlorophyll content
basis, and also the specific leaf area at all phosphorus levels. There was no significant difference between chlorophyll
a+b concentration and chlorophyll fluorescence kinetic parameters (Fv/Fm, Rfd) of AM and NAM plants.
Results support the hypothesis, that mycorrhiza enhance plant photosynthesis irrespectively of soil phosphorus content and
plant mycorrhizal dependency.
Kĺrén, O.
Effects of air pollution and forest regeneration methods on the community structure of ectomycorrhizal fungi. (full thesis online) Doctor's dissertation.
ABSTRACT:
This thesis describes the ectomycorrhizal community and how it is affected by nitrogen fertilization and forest regeneration methods. Fertilizer treatments included
ammonium sulphate (NS), lime +P+K+Ca+Mg+S (N-free) and ammonium nitrate, applied in spruce (Picea abies) stands in south Sweden and a pine (Pinus sylvestris)
stand in north Sweden. None of the fertilizers decreased the proportion of short-roots colonized by ectomycorrhizal fungi. Estimations of fungal biomass of short-roots in
NS and N-free treatments confirmed this. These results contrast with the 60-100% decreases in sporocarp production of ectomycorrhizal fungi reported by other
investigators. Molecular methods were used to identify ectomycorrhizal fungi on short-roots after testing their applicability in a separate study. N fertilization had a
pronounced effect on the species composition on mycorrhizal roots. The decreased sporocarp production of ectomycorrhizal fungi was suggested to depend on a
decreased abundance of species sensitive to N, decreased total allocation of carbohydrates to the fungi, and a changed carbohydrate allocation within the fungi.
A second study investigated the community structure of ectomycorrhizal fungi in 11 pine stands in central Sweden. Three stands ("O") consisted of 150-year-old,
unmanaged forests, and the remaining were 30-40 years old. Of the latter, four were the result of regeneration by planting on clear-cuts ("P"), and four developed under
shelterwood trees that were successively removed ("S"). Mycorrhizal roots, sampled in 1995 and sporocarps (in 1995-96) were identified. The number of species found
as mycorrhizas or as sporocarps was lowest in P, whereas species richness was similar in S and O. The species compositions of mycorrhizas or sporocarps were
least similar between P and O, but more similar between S and O. Between 45-90% of the mycorrhizas were formed by species not observed in the sporocarp inventory.
Multivariate analyses indicated that species composition of ectomycorrhizal fungi was correlated with the age of the forest, soil factors which were partly correlated with
age and to some extent also type of regeneration method.
It is suggested that nitrogen deposition and N-fertilization reduce the diversity of ectomycorrhizal fungi. Effects of forest regeneration methods appear less pronounced,
but fungi restricted to old forests may need protection.
ACCESSION NO.: AAG9900668
TITLE: EFFECTS OF SOIL HEAVY METAL CONTAMINATION AND
REMEDIATION ON THE SIZE, ACTIVITY, AND STRUCTURE OF SOIL
MICROBIAL COMMUNITIES
AUTHOR: KELLY, JOHN JOSEPH
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: RUTGERS THE STATE UNIVERSITY OF NEW JERSEY - NEW
BRUNSWICK; 0190
ADVISER: Director: ROBERT L. TATE, III
SOURCE: DAI, VOL. 59-08B, Page 3881, 00239 Pages
DESCRIPTORS: BIOLOGY, MICROBIOLOGY; AGRICULTURE, SOIL SCIENCE;
ENVIRONMENTAL SCIENCES; BIOLOGY, ECOLOGY
ABSTRACT: Heavy metal contamination and remediation of sites
impacted by heavy metals are significant environmental
issues, due to the fact that heavy metal contamination
can result in losses in soil quality. To prevent
ecosystem degradation and to determine the effectiveness
of remediation, sensitive methods are needed to assess
the impacts of heavy metals. Due to their sensitivity to
heavy metals, soil microbial communities could be useful
as indicators of heavy metal impacts. In this
dissertation, two techniques for analysis of microbial
community structure, BIOLOG and the Phospholipid Fatty
Acid (PLFA) assay, were applied in conjunction with
measures of microbial community size (plate counts and
biomass) and activity (dehydrogenase activity) to
several metal impacted soils. The application of these
assays to soils in the vicinity of a zinc smelter
indicated that high level metal contamination had
resulted in decreases in microbial population size and
activity, and changes in BIOLOG and PLFA profiles,
including decreases in indicator fatty acids for fungi,
actinomycetes, gram positive bacteria, and arbuscular
mycorrhizal fungi. The analysis of remediated soils from
this smelter site indicated that remediation had
resulted in increases in microbial population size and
activity, as well as increases in indicator fatty acids
for fungi, actinomycetes and gram positive bacteria,
suggesting recovery of microbial populations with
remediation. The addition of zinc to soils in the
laboratory did not have a similar long term impact on
microbial population size. However, zinc amendment in
the laboratory did result in a long term decrease in
microbial community activity and long term shifts in
BIOLOG and PLFA profiles similar to the shifts seen for
the zinc smelter soils. Analysis of microbial
communities from a sludge application study site
indicated that the elevated metal levels caused by
sludge application had resulted in changes similar to
those observed for the smelter soils: decreased
microbial activity, shifts in PLFA profiles, and
decreases in indicator fatty acids for fungi,
actinomycetes, and arbuscular mycorrhizal fungi.
However, sludge applied metals did not result in shifts
in BIOLOG metabolic profiles. These results indicate the
utility of microbial community analysis for assessing
the impacts of soil heavy metal contamination.
ACCESSION NO.: AAG9823054
TITLE: DEVELOPMENT OF ECTOMYCORRHIZAL MODEL SYSTEM FOR
IDENTIFICATION AND CHARACTERIZATION OF
"SYMBIOSIS" ASSOCIATED GENES FROM LACCARIA
BICOLOR X PINUS RESINOSA (MALATE SYNTHASE,
GLUCOSE, MRNA, RAS SIGNALING)
AUTHOR: KIM, SUNG-JAE
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: MICHIGAN TECHNOLOGICAL UNIVERSITY; 0129
ADVISER: Adviser: GOPI K. PODILA
SOURCE: DAI, VOL. 59-01B, Page 0080, 00178 Pages
DESCRIPTORS: BIOLOGY, MOLECULAR; AGRICULTURE, PLANT
PHYSIOLOGY;
BIOLOGY, BOTANY
ABSTRACT: An ectomycorrhiza is the complex symbiotic interaction between a plant's roots and a compatible ectomycorrhizal fungus. To better utilize the ectomycorrhizal fungi for increased yield of trees and improved forest health, we need to understand how the fungus perceives plant signals and affects fungal gene expression during ectomycorrhiza formation. An in vitro model system has been developed to study the changes in gene expression associated with the establishment of the symbiotic relationship. mRNA differential display was used to identify and facilitate the cloning of fungal genes induced during the very early stages of ectomycorrhiza formation. One of these differentially expressed cDNAs contained unusually large numbers of evolving repeats in its predicted protein sequence and shares similarity to other proteins known to be involved in signal transduction during the establishment and maintenance of
mycorrhiza, cDNAs encoding the signal transduction proteins, ras, and glucose regulated protein
(GRP) were cloned and characterized from L. bicolor. Northern blot results suggest the ras signaling pathway which includes GRP, ras and the ras-related r48PF gene may take part in ectomycorrhizae colonization and differentiation.
Because other ectomycorrhizal systems show induction of biosynthetic, metabolic genes and cell wall
synthesis genes, the glyoxal malate synthase cDNA and chitin synthase genomic fragment were also cloned and characterized from L. bicolor. Changes in gene expression may occur by developmental and
metabolic changes for the symbiotic initiation and function. The connection among cytoskeleton/cell wall
reorganization, biosynthetic, metabolic genes and signal transduction pathway was used to propose a hypothetical signal transduction model for L. bicolor in response to host plant (red pine). Genomic southern results of ras, GRP, malate synthase and chitin synthase indicated that these are single copy genes. These symbiosis-related genes can be tested for their functional significance for
the establishment of red pine mycorrhizae through gene displacement in the near future.
ACCESSION NO.: AAG9823444
TITLE: ECOLOGY OF GLOMALEAN FUNGI IN A 45 YEAR OLD FIELD ON
BRUNSWICK SHALE SOILS IN EASTERN PENNSYLVANIA
(ENDOMYCORRHIZAE, FUNGAL SUCCESSION)
AUTHOR: KYDE, MARION M.
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: RUTGERS THE STATE UNIVERSITY OF NEW JERSEY - NEW
BRUNSWICK; 0190
ADVISER: Director: ANN BROOKS GOULD
SOURCE: DAI, VOL. 59-02B, Page 0480, 00133 Pages
DESCRIPTORS: AGRICULTURE, PLANT PATHOLOGY; BIOLOGY, ECOLOGY
ABSTRACT: Endomycorrhizal diversity and colonization patterns and plant community indices were investigated in a 45 yr old field successional sere on Brunswick Formation red shale soil in eastern Pennsylvania. The site was dominated by Juniperus virginiana L. (eastern redcedar), Lonicera maackii Maxim (Amur honeysuckle), and Lindera benzoin (L.) Bloom (spice bush). Acer saccharum Marsh. (sugar maple), Fraxinus pennsylvanicus Marsh. (green ash), and Prunus serotina Ehrh. (black cherry) seedlings shared the understory with annual and perennial forbs and ferns. A 7.6 ha research plot was established on the site, divided into eight subplots, and diagonal transects were marked across each subplot as benchmarks for random sampling. Soil samples removed from each benchmark were assayed for endomycorrhizal activity in 1991 December and 1992 June and September. The host plant associated with each soil sample was recorded.
Mycorrhizal colonization of bioassay roots was highest in September, lowest in December, and differed
among subplots at each sample date. Mycorrhizal activity was poorly correlated with soil edaphic factors.
Plant diversity was highest in June (due to the presence of summer annuals), lowest in December, and differed among subplots only at the June sampling date. Plant species highest in mycorrhizal infectivity included eastern redcedar, sugar maple, and Amur honeysuckle. In 1993 June, six known (Acaulospora spinosa, Gigaspora gigantea, Glomus aggregatum, G. constrictum, G. occultum, and Scutellospora calospora) and two unidentified (Glomus sp. and Scutellospora sp.) Glomalean species were recovered from trap cultures grown in rhizosphere soil sampled from the root systems of host plants within each subplot. Of these, S. calospora was the most abundant. This is the first report of Glomalean species from Eastern Pennsylvania.
The number of abundant species and diversity in the total plot were high, dominance was low, and
evenness was intermediate. Weak, but significant correlations were evident between mycorrhizal infectivity and plant dominance (negative relationship) and plant diversity and number of abundant species (positive relationships). A consistent association of A. spinosa with Alliaria officionalis (garlic mustard), an introduced cruciferous biennial, was noted and suggested for further study.
Mankani, Shrinivas. 1998. Response of Papaya (Carica papaya L.) to vesicular arbuscular mycorrhizal fungi at graded levels of Phosphorous. University of Agricultural Sciences, Dharwad- 580 005 Karnataka state, India.
ACCESSION NO.: AAG9836335
TITLE: THE DYNAMICS OF THE GRASS-MYCORRHIZAL FUNGI ASSOCIATION
IN NUTRIENT-POOR WETLANDS (MYCORRHIZAL FUNGI, PANICUM
HEMOTIOMON, LEERSIA HEXANDRA, PHOSPHORUS, NITROGEN)
AUTHOR: MILLER, SUSAN PAULETTE
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: UNIVERSITY OF GEORGIA; 0077
ADVISER: Director: REBECCA R. SHARITZ
SOURCE: DAI, VOL. 59-06B, Page 2548, 00151 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY; BIOLOGY, BOTANY; AGRICULTURE, SOIL
SCIENCE
ABSTRACT: The arbuscular mycorrhizal fungi are important symbionts
in terrestrial plants; by infecting plant roots and
extending hyphae into the soil they increase the
absorptive area of the root system and the delivery of
nutrients to the plant. The fungi are obligate aerobes
and therefore their ability to form associations with
wetland and aquatic plants has long been in question,
although many investigators have found the fungi in
these plants. This research examines the interaction of
flooding with levels of fungal infection in two semi-
aquatic grasses (Panicum hemitomon and Leersia hexandra)
in wetlands of the southeastern U.S. Coastal Plain.
The first chapter showed that growth of P. hemitomon and
L. hexandra in the Carolina bays was limited by a lack
of soil nutrients. Phosphorus was the primary limiting
nutrient and nitrogen was secondary. The field study in
Chapter 2 showed that the two grasses were mycorrhizal
in the natural wetland habitats, and the infection rates
were strongly correlated to relative water depth. While
mycorrhizal infection rates decreased with increasing
water depth, active infection occurred in the plants
from the wettest portions of the bay. The experiment
described in Chapter 3 showed that controlled water
regimes were a large factor in determining the levels of
mycorrhizal infection in the grasses. Plants growing in
soil that remained wet for the course of the experiment
developed almost no infection, while plants in soil that
remained free-draining developed high levels of
infection. Intermediate levels of infection were found
in plants that had water regimes that shifted from 'wet-
to-dry', and from 'dry-to-wet'. The experiment also
showed that plant-fungal associations that formed while
the soil was dry were maintained after flooding.
Colonization by mycorrhizal fungi had a positive
influence on plant size and phosphorus content in every
water level treatment. Chapter 4 surveyed the
distribution of mycorrhizal species present along a dry-
to-wet gradient in two Carolina bays. Although the exact
pattern differed between the two bays, zonation of the
mycorrhizal species along a dry-to-wet gradient occurred
in both, and certain fungal species were more abundant
in either the wetter or drier areas.
ACCESSION NO.: AAGC632354
TITLE: THE EXTERNAL MYCORRHIZAL MYCELIUM: GROWTH AND
INTERACTIONS WITH SAPROPHYTIC MICROORGANISMS
AUTHOR: OLSSON, PAL AXEL
DEGREE: FIL.DR
YEAR: 1998
INSTITUTION: LUNDS UNIVERSITET (SWEDEN); 0899
SOURCE: DAI, VOL. 59-02C, Page 0328, 00099 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY
ISBN: 91-7105-091-4
PUBLISHER: DEPARMENT MICROBIAL ECOLOGY, ECOLOGY BUILDING,
LUND UNIVERSITY, S-223 62 LUND, SWEDEN
ABSTRACT: The interactions between external mycorrhizal mycelia and saprophytic microorganisms were studied in experiments with growth chambers specially designed to enable the mycelia to develop in root-free soil compartments. The growth of the mycorrhizal mycelia was estimated by use of biochemical signature compounds. It was shown possible to estimate the biomass of the external mycelium of different arbuscular mycorrhizal fungi by use of the signature fatty acid 16:1$omega$5 in an agricultural soil and in dune sand. The amount of fatty acid 16:1$omega$5 was estimated as indicator both of phospholipids (as PLFA) and neutral lipids (as NLFA). The results indicated that PLFAs reflect mycellum structures of the AM fungi and NLFAs storage structures.
The amounts of NLFA 16:1$omega$5 correlated well with the number of spores formed by a mycelium, but results indicated that accumulation of neutral lipids may occur before sporulation. It is suggested that the ratio between neutral lipids and phospholipids indicates the carbon allocation to storage structures in AM fungi. No effects of the AM mycellum on the bacterial community were recorded in an agricultural soil, even though the AM mycellum constituted a large part of the biomass. In a study involving calcareous dune sand, the growth of the external AM mycellum decreased the amount of PLFA 18:2$omega$6,9, indicating negative effects on growth of saprophytic fungi.
Ectomycorrhizal mycelia of six different species reduced bacterial activity, estimated as thymidine incorporation, in experiments with a sandy soil. In these experiments no negative effect on bacterial biomass was observed. In a study on pines growing for eight months in a peat/sand mixture, both bacterial activity and biomass were lowered due to mycorrhizal inoculation. However, in the soils to which primary minerals as apatite and biotite had been added, the growth of Suillus variegatus increased bacterial activity. This demonstrated that, under certain circumstances, ectomycorrhizal fungi may contribute to a significant carbon input to the soil which stimulates bacterial growth plant shoots or roots was detected in either the field or greenhouse studies.
ACCESSION NO.: AAG9907519
TITLE: INTERACTIONS OF ARBUSCULAR MYCORRHIZAL FUNGI WITH HEAVY
METALS (GLOMUS ETUNICATUM, CADMIUM, LEAD, ZINC, METAL
TOLERANCE)
AUTHOR: PAWLOWSKA, TERESA ELZBIETA
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: UNIVERSITY OF MINNESOTA; 0130
ADVISER: Adviser: IRIS CHARVAT
SOURCE: DAI, VOL. 59-09B, Page 4582, 00156 Pages
DESCRIPTORS: BIOLOGY, BOTANY; BIOLOGY, ECOLOGY; BIOLOGY, MICROBIOLOGY
ABSTRACT: Arbuscular mycorrhizal (AM) fungi (Glomales,
Zygomycetes) may have a significant role in ameliorating
heavy metal toxicity in plants as well as in
contributing to the enhancement of detrimental metal
effects. Different aspects of interactions of AM fungi
with heavy metals were studied to elucidate the
mechanisms of metal tolerance in glomalean fungi.
The results of a study on the effects of
phytoremediation practices on a community of AM fungi
indigenous to the metal contaminated Pig's Eye landfill,
St. Paul, MN, indicated that use of nonmycorrhizal plant
species may negatively affect survival of glomalean
fungi.
Monoxenic cultures of Glomus etunicatum in association
with excised Ri T-DNA transformed carrot roots were
established as a research tool to study the responses of
glomalean fungi to metal stress. To elucidate whether AM
fungi synthesize intracellular metal chelators,
phytochelatins, germinating chlamydospores of G.
etunicatum and G. intraradices were exposed to elevated
concentrations of Cd, Cu, Pb and Zn. A gel
electrophoresis assay of cell-free extracts from
chlamydospores germinated in Cd-enriched environment
revealed presence of peptide species that migrated at a
similar rate to phytochelatin standards. No such
peptides were detected in response to Cu, Pb, or Zn, or
under control conditions.
The effects of Cd, Pb and Zn exposure on different
stages of the glomalean life cycle were examined in
vitro. Despite long term culturing under similar low-
metal conditions, ecotypes of the two studied species,
G. etunicatum and G. intraradices, exhibited intrinsic
species-specific levels of metal tolerance. A unique
response involving increased germ tube extension was
observed in G. intraradices exposed to Cd and Pb stress.
Moreover, germ tube elongation was negatively correlated
with formation of vegetative spores by germ tubes
arising from resting spores of G. intraradices exposed
to Cd and Pb. Inhibitory metal effects on extraradical
mycelium and sporulation in G. intraradices were
localized to the metal enriched portions of the fungal
habitat. Patterns observed in Glomus intraradices germ
tube elongation and vegetative spore formation, as well
as extraradical mycelium growth and sporulation in
habitats with elevated metal concentrations may be
considered as functional equivalents of a metal
avoidance strategy.
Author: Ryan, Megan
Title: The ecology of VAM fungi in contrasting Australian agricultural systems
University: Australian National University, Canberra, ACT, Australia
Degree: PhD
Year: 1998
Supervisor: Julian Ash
More Details: Megan Ryan, CSIRO plant industry, GPO Box 1600, Canberra, ACT,
Australia, 2601; m.ryan@pican.pi.csiro.au
Abstract
The thesis presents the results of a field-orientated project that examined
the ecology of VAM fungi in agricultural systems in SE Australia between
1993 and 1996. Ecological trends involving VAM fungi, phosphorus (P) and
plant growth were investigated using 23 farm pairs consisting of adjacent
commercial farms under contrasting farm management strategies; conventional
and alternative. The conventional farmers applied large inputs of soluble P
fertilisers, while the alternative farmers either applied no P fertilisers
or applied the relatively insoluble rock phosphate. This design allowed the
long term effects of variations in P inputs to be examined on replicated
sites. The paired farms were located in two contrasting agricultural
commodity production systems; a dryland (mixed) cereal-livestock system
which alternated between annual pasture and annual crops, and a dairy system
which consisted of permanent, perennial, irrigated pasture. Farms of the
same commodity production system and farm management strategy were regarded
as replicates. The project was designed to test hypotheses about the
ecology of VAM fungi at both the scale of the VAM fungi-plant relationship
and, more broadly, at the scale of ecosystem-level processes. A major aim
was also to test the hypothesis that the biological processes in
conventional and alternative agricultural systems are fundamentally different.
For both wheat crops and subterranean clover in pastures on the mixed
farms, and the three major species (rye grass, paspalum and white clover) in
the pastures on the dairy farms, VAM colonisation levels were consistently
strongly negatively correlated with soil extractable P and plant P
concentrations. The negative influence of P was confirmed in glasshouse
trials. Total soil N and plant N concentrations were positively correlated
with VAM colonisation in some instances. On the mixed farms, a severe
drought markedly reduced VAM colonisation in annual crops in 1994 and
appeared to reduce the VAM inoculum potential of the soil. On individual
dairy farms, VAM colonisation levels in pasture did not vary greatly over a
four year period.
Due to the addition of fertilisers containing soluble P, conventional
farms consistently had higher soil extractable P concentrations and
significantly lower VAM colonisation levels than alternative farms. No
other farm management practices specific to conventional or alternative
management were found to significantly affect VAM colonisation levels.
Thus, VAM fungi made a greater contribution towards nutrient uptake on the
alternative farms, however, in terms of yield, this did not compensate for
the non-application of soluble P fertilisers.
Studies on the effect of mycorrhizal fungi on the growth of Acacia nilotica seedlings in the nursery.
R.S. Saravanan email. PhD. University of Madras, August 1998. Supervisor: Prof. K. Natarajan, CAS in Botany, University of Madras, Guindy Campus, Chennai 600 025, India.
Populations of ectomycorrhizal basidiomycetes of the genus Laccaria, introduced or indigenous, under
Douglas fir (Pseudotsuga menziesii).
Marc-André SELOSSE, email, website. PhD. F. Le
Tacon (major professor), Institut National de la Recherche Agronomique in Nancy (France).
ABSTRACT: Laccaria are basidiomycetes that form symbiosis with trees (mycorrhizas) and are inoculated in nurseries under trees
like Douglas fir (Pseudotsuga menziesii). The outplanting of trees raises the questions of the fate of the inoculant as well as its effect
on natural populations. We studied a plantation from the Ničvre (France). In 1987, it received in separate plots trees that were (1)
inoculated by the American strain L. bicolor S238N or (2) inoculated by the French strain, L. bicolor 81306 or (3) uninoculated
(controls).
1100 sporophores of Laccaria spp. were collected in 1994 to 1997 over 1000 m2. Genetic markers amplified by PCR were
obtained: (1) nuclear and mitochondrial ribosomal DNA (2) RAPD markers, whose meiotic segregation was followed. The two
inoculant persist on inoculated plots 10 years after outplanting. None of the other genets suggested any selfing of the inoculants
(P<8.10-4). For L. bicolor S238N, no introgression was detected, in spite of its interfertility with European genets. For L. bicolor
81306, that is not divergent from the European genets, this question is not solved.
Inoculant strains do not invade uninoculated plots, except one that is invaded by both inoculants. The strain 81306 colonized this plot
vegetatively, at a rate of 1.1 m/yr. Indigenous genets are small and not fragmentated (<3,3 m across, density 500 genets/ha) and are
not affected by the presence of inoculant strains. This persistence, that improves tree growth but does not disturb indigenous
populations, strongly supports the use of ectomycorrhizal strains in nursery.
ACCESSION NO.: AAGNQ28376
TITLE: ROLE OF ARBUSCULAR MYCORRHIZAL FUNGUS (GLOMUS
INTRARADICES SCHENCK AND SMITH) COLONIZATION IN DROUGHT
TOLERANCE OF MAIZE (ZEA MAYS L.)
AUTHOR: SUBRAMANIAN, KIZHAERAL S.
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: UNIVERSITY OF OTTAWA (CANADA); 0918
ADVISER: Adviser: CHRISTIANE CHAREST
SOURCE: DAI, VOL. 59-07B, Page 3282, 00198 Pages
DESCRIPTORS: BIOLOGY, PLANT PHYSIOLOGY; AGRICULTURE, PLANT
PHYSIOLOGY; BIOLOGY, ECOLOGY; AGRICULTURE, AGRONOMY;
AGRICULTURE, PLANT CULTURE; BIOLOGY, BOTANY
ISBN: 0-612-28376-3
ABSTRACT: The purpose of this thesis was to study the potential
factors involved in mycorrhizae-assisted drought
tolerance in maize (Zea mays L.). We hypothesized that
the AM colonization promotes drought tolerance of the
host plant. This may be as a consequence of altered
water relations, metabolism or nutritional status of the
host plant. These changes enable the host plant to
sustain water deficit conditions and recover more
rapidly when irrigation is restored. To test these
hypotheses, the five objectives were: (i) To measure the
physiological responses in maize plants in the absence
or presence of AM colonization; (ii) To examine the
metabolic changes in these plants; (iii) To determine
the host plant nutritional status in order to assess the
ability of AM plants to support kernel development; (iv)
To evaluate the drought recovery of maize and (v) To
examine the effects of AM colonization on nitrogen
assimilation in maize as a potential factor in drought
tolerance.
The AM colonization in maize had a beneficial effect on
the water relations and leaf enlargement under water
deficit conditions. In comparison to non-AM plants, the
AM colonized plants maintained higher (less negative)
leaf water potential (LWP) and lower stomatal resistance
even after 3 wks of withholding water at the tasselling
stage.
Mycorrhizal colonization improved the nutritional status
of maize through the enhanced uptake of N, P and other
micronutrients. This indirectly helps the AM plants to
utilize the soil available moisture more effectively.
Our data indicated that the total N content in drought-
stressed maize plants were nearly doubled in the
presence of AM association.
The overall results support the hypothesis that the AM
colonization assists the two tropical maize cultivars to
withstand under moderate drought conditions. The drought
tolerance was achieved due to the physiological,
metabolic and nutritional modifications in the host
plant. These changes can be primarily related to the
improved host plant water relations and the nutritional
status, especially N and P. This thesis has provided new
insights into the changes in N acquisition and
assimilation of mycorrhizal plants under drought
conditions. The findings of this thesis support the idea
that AM fungi are one of the major biological components
in the rhizosphere needed to accomplish the goal of
sustainable agriculture in arid and semiarid areas.
(Abstract shortened by UMI.)
ACCESSION NO.: AAGC630315
TITLE: DYNAMICS AND FUNCTIONS OF THE MICROBIAL
COMMUNITIES WITHIN PINE MYCORRHIZOSPHERES (PINUS SYLVESTRIS,
ECTOMYCORRHIZAL FUNGI, SOIL BACTERIA)
AUTHOR: TIMONEN, SARI SINIKKA
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: HELSINGIN YLIOPISTO (FINLAND); 0592
SOURCE: DAI, VOL. 59-02C, Page 0336, 00128 Pages
DESCRIPTORS: BIOLOGY, MICROBIOLOGY; AGRICULTURE, FORESTRY AND
WILDLIFE; BIOLOGY, ECOLOGY; AGRICULTURE, SOIL SCIENCE
ISBN: 951-45-8030-3
PUBLISHER: GUMMERUS KIRJAPAINO OY, SAARIJARVEN LATOMO JA
PAINO, P.O. BOX 25, SF-431 01 SAARIJARVI, FINLAND
ABSTRACT: Forests are complex biological systems constructed of interacting organisms from all trophic levels. In order to sustainably manage and manipulate forest ecosystems we need to know the key interplayers in the system as well as have an outline of their functions. Characterising both the fungi and the bacteria associated with Scots pine roots in their natural environment and gaining some information about nutrient uptake and defence related enzymes in intact pine ectomycorrhizospheres is a beginning of a better understanding of boreal forest ecosystems. In this study the activities and microbial diversity of the functionally distinct compartments of intact ectomycorrhizospheres grown in natural forest
soil were comprehensively investigated for the first time.
Dry pine forest humus was shown to contain a lot of viable propagules of different ectomycorrhizal
fungi. Ectomycorrhizal fungi of different species as well as distinct strains of the same species coexisted
regularly in the roots of one seedling. Both inter- and intra-specific interactions between ectomycorrhiza
forming fungi in Scots pine rhizosphere were beneficial, rather than detrimental, to the survival or growth of Scots pine seedlings.
The isozyme expression of nutrient mobilising and defence related enzymes of Scots pine and mycorrhizal
fungi in intact ectomycorrhizospheric systems was affected by the specific environment of each compartment and under local regulatory control. An example of the polarised functions of intact ectomycorrhizal fungi was demonstrated e.g., by showing that the fine outermost hyphae were more efficient in the uptake of phosphorus than strands. Different fungal species displayed dissimilar activities.
Bacterial populations of Scots pine mycorrhizospheres varied in their numbers and composition according
to the fungal species, soil type and specific mycorrhizospheric location. A great micro scale heterogeneity was observed also within superficially similar locations.
ACCESSION NO.: AAG9836846
TITLE: CAUSES AND CONSEQUENCES OF MONODOMINANCE IN TROPICAL
LOWLAND FORESTS (GILBERTIODENDRON DEWEVREI, CONGO)
AUTHOR: TORTI, SYLVIA DENISE
DEGREE: PH.D.
YEAR: 1998
INSTITUTION: THE UNIVERSITY OF UTAH; 0240
ADVISER: Adviser: PHYLLIS COLEY
SOURCE: DAI, VOL. 59-06B, Page 2550, 00122 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY
ABSTRACT: This dissertation explores the causes and consequences
of tropical monodominant forests. Monodominant forests
are defined as forests in which >60% of the canopy
is comprised of a single tree species. I studied the
monodominant Gilbertiodendron dewevrei forest of
northeastern Congo.
I performed the first test of the ectomycorrhizal
hypothesis for monodominance by surveying the
mycorrhizal status of dominant, as well as other common,
but not dominant, species in the forest. The survey
revealed that two dominant species form both
ectomycorrhizae (EM) and vesicular-arbuscular
mycorrhizae (VAM), whereas another dominant, forms only
vesicular-arbuscular mycorrhizae. These results, along
with those of the other species in this forest,
demonstrate the relationship between EM and tropical
monodominance is complex and show that EM cannot explain
all cases of tropical monodominance.
I also tested the hypothesis that dominant species
experience an advantage over other plant species because
they invest heavily in defenses and suffer relatively
less herbivory and pathogen damage when they are
seedlings and saplings. I found no support for this
hypothesis, as the dominant species in the Congo
suffered the heaviest rates of damage.
In addition to the ectomycorrhizal and herbivory
hypotheses, I tested for differences in the rates of
decomposition, the availability of nitrogen and the
amount of light penetration to the understory in both
forest types. In all of these cases, there were striking
differences between the two forest types with slower
decomposition, less nitrogen availability and deeper
shade in the Gilbertiodendron forest.
My results suggest that the Gilbertiodendron maintains
its dominance by creating an understory environment that
is inhospitable to other species. Moreover, saplings of
Gilbertiodendron seem well adapted to survive in the
understory of the Gilbertiodendron forest and hence, a
positive feedback loop is created wherein the juveniles
of the dominant species are the only species able to
tolerate the stressful environment created by the adult.
In general, all tropical monodominant species share a
suite of traits in both the adult and juvenile stages
that allow them to establish and maintain dominance. In
addition, historical factors affect the ability of a
potentially dominant species to achieve dominance.
ACCESSION: 39220227
AUTHOR:
Walker, John F., 1966-
TITLE: The inhibitory effect of Rhododendron
maximum L. (Ericaceae) thickets on mycorrhizal colonization
of canopy tree seedlings
PLACE: [Blacksburg, Va. :
PUBLISHER: University Libraries, Virginia
Polytechnic Institute and State University,
YEAR: 1998
PUB TYPE: Machine-readable data
NOTES: Title from electronic submission form.
Vita.
Abstract.
Thesis (M.S.)--Virginia Polytechnic Institute and State
University, 1998.
Includes bibliographical references.
Author's abstract: Thickets of Rhododendron maximum (Rm) in
the southern Appalachians impose severe limitations on the
regeneration of hardwood and coniferous seedlings.
Interactions between Rm thickets and ectomycorrhizal
colonization were examined to explain seedling inhibition.
Experimental blocks were established in and out of Rm
thickets in a mature, mixed hardwood/conifer forest in Macon
County, North Carolina. Planted seedlings of red oak (Quercus
rubra) and hemlock (Tsuga canadensis) were harvested at the
end of the first and second growing seasons. Litter
manipulation had no effect on total mycorrhizal colonization.
Mycorrhizal colonization and ramification index (#
mycorrhizae cm-1) were depressed and colonization by
Cenococcum geophilum increased in blocks with versus without
Rm. After the first year, percent colonization of T.
canadensis not in Rm thickets (62 %) was three times higher
than in Rm thickets (19%), and the ramification index was
increased by more than a factor of four (2.83 versus 0.61).
Mycorrhizal colonization levels were correlated with root
weight and shoot weight in both hemlock and oak seedlings,
but did not explain most of the variation observed.
Sporocarps of 69 putatively ectomycorrhizal species were
collected on the blocks. Species diversity and overall
community structure was similar in and out of Rm thickets.
Individual species, i.e. Lactarius speciosus and Russula
krombholzii, were significant indicators of forest without Rm
thickets. Rhododendron maximum thickets probably affect the
process of mycorrhization. The reduced level of mycorrhizal
capacity under Rm thickets could be a factor in the increased
seedling failure in Rm thickets.
System requirements: PC, World Wide Web browser and PDF
reader.
Available electronically via Internet.
SUBJECT:
ectomycorrhizae -- mycorrhizal colonization --
fungus community -- rhododendron -- tree seedling
ACCESS: http://scholar.lib.vt.edu/theses/delayed/etd-42198-15118/etd-title.html
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