Mycorrhizal Theses and Dissertations

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1997 * * * * * * * * * * * * * * * * * * * * * * *

ACCESSION NO.: AAG9817970
TITLE: ROLE OF FUNGAL ROOT ENDOPHYTES IN ESTABLISHING FOURWING SALTBUSH (ATRIPLEX CANESCENS (PURSH) NUTT.) SEEDLINGS IN ARID ECOSYSTEMS
AUTHOR: AFZAL, JAVED
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: NEW MEXICO STATE UNIVERSITY; 0143
ADVISER: Chair: REX D. PIEPER
SOURCE: DAI, VOL. 58-12B, Page 6319, 00075 Pages
DESCRIPTORS: AGRICULTURE, RANGE MANAGEMENT; BIOLOGY, MICROBIOLOGY; AGRICULTURE, AGRONOMY
ABSTRACT: Native plants on arid rangelands are extensively colonized by non-destructive fungal root endophytes. Their proposed function in nutrient stressed environments is to access nutrients from recalcitrant organic and inorganic sources and supply them to the host. Four greenhouse and one field experiments were conducted to determine if these fungal endophytes enhanced growth for fourwing saltbush (Atriplex canescens) seedlings. A low nutrient sandy soil from the Jornada Experimental Range was compared with a nutrient free silica sand. Soils and plant litter were heated to eliminate soil fungi and bacteria and compared to nonheated materials. Seed was disinfested to eliminate seedborn fungi and compared with nondisinfested seed.

Neither seed disinfestation nor heating of soil or plant litter eliminated root colonization, but these treatments reduced fungal effects. Inoculation with fungal endophytes or isolates from roots of mature plants did not enhance seedling growth, neither were they pathogenic, but suggested that a suite of fungi colonize the host. Different fungi may favorably affect the host over different growth or seasonal stages. Significant growth response was observed in seedlings growing in soil vs. silica sand with roots being extensively colonized by septate fungi. Lesser, but significant responses were observed with supplemented plant litter. Roots of fourwing saltbush seedlings in Pakistan were extensively colonized by fungi and responded to supplemented sheep manure and wheat straw.

Ratios of VAM vs. septate fungi differed between Pakistan and New Mexico. This difference was likely due to differences in environmental conditions. It was concluded that septate fungi enhanced nutrient uptake from sandy soils and plant litter. Observed septate fungi are not currently classified as mycorrhiza, yet they bear similarities in colonization and function to classical mycorrhizas. It's presumed that they are adapted to specific environmental stresses and have a primary function of accessing nutrients from organic and inorganic substrates and transferring them to the host. In fourwing saltbush they apparently are seedborne and colonize seedling to insure nutrient uptake.

ACCESSION NO.: AAG1386838
TITLE: ARBUSCULAR MYCORRHIZAL FUNGI AND TRICHODERMA HARZIANUM IN RELATION TO BORDER CELL PRODUCTION AND FUSARIUM ROOT ROT OF ASPARAGUS (GLOMUS INTRARADICES, FUSARIUM OXYSPORUM)
AUTHOR: ARRIOLA, LAURA LYNN
DEGREE: M.S.
YEAR: 1997
INSTITUTION: MICHIGAN STATE UNIVERSITY; 0128
SOURCE: MAI, VOL. 36-01, Page 0109, 00068 Pages
DESCRIPTORS: BIOLOGY, BOTANY; AGRICULTURE, PLANT PATHOLOGY
ABSTRACT: Four species from the family Amaranthaceae were studied to determine border cell (sloughed root cap cells) production and arbuscular mycorrhizal colonization. Border cells were produced by all species studied and the number of border cells increased with increasing root length until a maximum was reached at 25 mm.

Arbuscular mycorrhizal root colonization was found in all the Amaranthaceae species and was positively correlated with maximum border cell production. In a second study, commercially available forms of the arbuscular mycorrhizal fungus Glomus intraradices and Trichoderma harzianum were investigated as biocontrol agents of Fusarium oxysporum f. sp. asparagi inoculated (at high and low concentrations) asparagus. Death rates of biocontrol treated plants were less than half those of plants inoculated only with F. oxysporum. Shoot height, weight and number of shoots produced was greater in biocontrol treated plants than in plants inoculated only with F. oxysporum.

ACCESSION NO.: AAG9824558
TITLE: ASSESSMENT OF ARBUSCULAR MYCORRHIZA INOCULUM POTENTIAL (MYCORRHIZAL FUNGI, FLORIDA)
AUTHOR: BAKARR, MOHAMED IMAM
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: UNIVERSITY OF MIAMI; 0125
ADVISER: Supervisor: DAVID P. JANOS
SOURCE: DAI, VOL. 59-02B, Page 0489, 00114 Pages
DESCRIPTORS: BIOLOGY, BOTANY; BIOLOGY, ECOLOGY; AGRICULTURE, SOIL SCIENCE
ABSTRACT: Arbuscular mycorrhizae (AM) are essential for plant growth in soils of low fertility, but mycorrhiza formation under natural conditions can be constrained by limited inoculum. Assessment of mycorrhiza inoculum potential (MIP), defined as the capacity of AM fungi existing at a site to form sufficient mycorrhizae to influence host plant growth, is crucial to understanding the potential importance of mycorrhizae in the field. AM fungal propagules that comprise inocula in field soils include spores, mycorrhizal fragments, and intact hyphal networks attached to living roots. Techniques for assessment of MIP are based on soil extraction and manipulation which fragments roots and excludes hyphal networks. Extractive bioassay measures of MIP cannot provide information on mycorrhiza formation and function under field conditions. This dissertation reports experiments conducted to examine (1) effects of manipulating mycorrhizal fragments on their efficacy as inoculum, (2) the extent to which extractive bioassays agree with one another and can predict plant performance in the field, and (3) host plant effects on infectivity of hyphal networks.Mycorrhizal fragments of 100 cm total length cut into 0.5 cm, 1.0 cm, 2.0 cm and 4.0 cm lengths produced different amounts of initial colonization in Psidium guajava seedlings roots. Colonization was maximized by the 1.0 cm and 2.0 cm fragments. Freshly collected root inoculum added to pots containing sterile soil and planted with Abutilon theophrasti seedlings at 0, 3, 6, 9, and 18 days after inoculation of pots showed a decline in infectivity after 6 days. These results suggest that manipulation of root fragments in extractive bioassays may affect their contribution to MIP.

The extent to which extractive bioassays agree with each other was determined in a field experiment on ten adjacent 6m x 6m plots established in a grassy field. I mowed five of the plots over a three month period to produce differences in the occurrence of AM fungi. I counted spores and sporocarps, performed extractive bioassays on soil samples, and examined colonization in root samples from the plots. Spore and sporocarp counts were not correlated with Most Probable Number estimates and direct bioassay measures. Extractive bioassays, however, were significantly correlated with each other. No MIP measure was correlated with growth of P. guajava seedlings transplanted to the plots and grown for ten weeks. Inocula in the plots may have exceeded the amount necessary to stimulate seedling growth, so that apparent variation in MIP was irrelevant. Host plants might encounter high MIP in the field because of the potential to attach to intact hyphal networks. I examined the inoculum potential of hyphal networks by removing shoots of mycorrhizal "donor" P. guajava plants growing in pots attached to established hyphal networks and assessing-consequent effects on mycorrhiza formation by "recipient" P. guajava seedlings. Mycorhiza formation was improved initially by donor decapitation, but growth of recipient seedlings was suppressed by the presence of just two donor shoots.

These studies suggest that MIP measures by extractive bioassay may not be reliable for management purposes because of potentially altered infectivity of propagules, and lack of correlation with plant performance under field conditions. Because mycorrhiza formation and effect on host plants can be difficult to predict in the field, the use of field bioassays to assess MIP is essential for management purposes.

ACCESSION NO.: AAG9735866
TITLE: PATTERNS OF ROOT COLONIZATION BY THE ARBUSCULAR MYCORRHIZAL FUNGUS GLOMUS INTRARADICES AND HOST PLANT RESPONSES (PHASEOLUS VULGARIS)
AUTHOR: BLEE, KRISTOPHER ALLEN
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: UTAH STATE UNIVERSITY; 0241
ADVISER: Major Professor: ANNE J. ANDERSON
SOURCE: DAI, VOL. 58-06B, Page 2854, 00129 Pages
DESCRIPTORS: BIOLOGY, MOLECULAR; BIOLOGY, CELL; AGRICULTURE, PLANT PATHOLOGY; BIOLOGY, ECOLOGY
ABSTRACT: Mycorrhizal hyphae were directed in their growth pattern in roots. Arbuscules produced by a single isolate of Glomus intraradices Schenck & Smith in roots of corn, wheat, carrot, clover, mung bean, and bean (Phaseolus vulgaris L.) were consistently limited to cortical cells immediately adjacent to the endodermis.

Two hypotheses for controlled growth of arbuscular mycorrhizal fungi in plants were examined: (1) activation of plant defenses by the fungus, and (2) availability of host-derived carbon to the fungus. Accumulations of mRNAs for the defense-related genes phenylalanine ammonia-lyase (PAL), chalcone synthase, chitinase (CHT), glucanase, and hydroxyproline-rich glycoprotein were examined in the roots of P. vulgaris colonized by G. intraradices. In situ hybridizations of colonized roots using probes for PAL and CHT showed accumulations of both transcripts changed only in arbusculated cells. Both young, finely branched arbuscules and older, clumped arbuscules displayed PAL and CHT message accumulations. PAL and CHT mRNA accumulations were greater in cortical cells containing young arbuscules than in cells containing clumped arbuscules. Intercellular hyphae and vesicles elicited no defense response. Because arbuscules in cells surrounding the endodermis are uniquely positioned to intercept the lateral movement of photosynthate out of the vascular cylinder, transcript levels for sucrose-metabolizing enzymes were examined in arbusculated cells. A cDNA was cloned from roots of P. vulgaris encoding a soluble acid invertase with potential vacuolar targeting. This clone and cDNAs for a Rhizobium-responsive sucrose synthase of soybean and a cell wall acid invertase of carrot were used as nucleic acid probes in in situ hybridizations of mycorrhizal roots. Transcript levels for cell wall acid invertase in arbusculated cells of carrot remained unchanged. Sucrose synthase mRNA levels were high in phloem tissues of the vascular cylinder of nonmycorrhizal and mycorrhizal roots of P. vulgaris. Strong endodermal cell-specific expression of the soluble acid invertase cDNA was observed in noncolonized and arbuscular mycorrhizal P. vulgaris roots. In addition, mycorrhizal roots of P. vulgaris showed increased transcript accumulation for the sucrose synthase and soluble acid invertase cDNAs that was limited to arbusculated cells.

ACCESSION NO.: AAG9734111
TITLE: LIPIDS: THEIR VALUE AS MOLECULAR MARKERS AND THEIR ROLE IN THE CARBON CYCLE OF ARBUSCULAR FUNGI (MYCORRHIZAE, RHIZOCTONIA, PYTHIUM)
AUTHOR: CALDERON, FRANCISCO JOSE
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: MICHIGAN STATE UNIVERSITY; 0128
SOURCE: DAI, VOL. 58-05B, Page 2230, 00154 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY; BIOLOGY, BOTANY
ABSTRACT: Arbuscular mycorrhizae are associations between fungi and the roots of vascular plants. Part of this dissertation is devoted to analyzing the fatty acid and sterols of mycorrhizal and non-mycorrhizal Sorghum with the aim of identifying universal molecular markers of mycorrhizal infection. The mycorrhizal fungi contain high amounts of unusual lipids that may be used to mark their presence in infected roots. My results show that phospholipid fatty acid 16:1, as well as campesterol are molecules that can be used to consistently identify mycorrhizal infection. In addition, lipid profiles may provide insight as to which fungal species is present in the roots.

In a second experiment, the fatty acids and sterols of several isolates of root pathogenic fungi were surveyed to assess the taxonomic value of lipid profiles. My results show that the genera Rhizoctonia and Pythium can be reliably identified because of their characteristic lipid composition. Another question that I address in this work is: What is the C turnover time of mycorrhizal lipids? For this purpose, I carried out a pulse-chase experiment in which I followed the incorporation and subsequent turnover of C in mycorrhizal lipids. Mycorrhizal and non-mycorrhizal plants were subjected to a pulse exposure to $sp{14}$CO$sb2$, followed by sequential harvesting. Infected plants assimilated more $sp{14}$C than non-mycorrhizal plants, and had a higher absolute and percentage allocation of $sp{14}$C to root tissue, below ground respiration, and soil. Despite the increased fixation of C by mycorrhizal plants, mycorrhizal shoots had reduced biomass. This indicates that the C drain imposed by the fungus results in a reduced shoot growth, suggesting that the mycorrhizal fungus was acting as a parasite. The pulse-chase experiment demonstrated that the lipids of mycorrhizal roots are a dynamic pool of C with measurable turnover of $sp{14}$C. The C turnover time of the mycorrhizal fatty acid 16:1 $omega$5 was calculated at 210 h$sp{-1}$. The lipids of non-mycorrhizal roots incorporated less radiolabel, underscoring the difference in the lipid C cycle between the arbuscular mycorrhizae and non-mycorrhizal roots. To my knowledge, this is the first measurement of the C turnover of a biomass component of the mycorrhizal fungus.

ACCESSION: 38983179
AUTHOR: Colgan, Wesley.
TITLE: Diversity, productivity, and mycophagy of hypogeous mycorrhizal fungi in a variably thinned Douglas-fir forest
YEAR: 1997
PUB TYPE: Book
FORMAT: 95 leaves, bound : ill. ; 29 cm.
NOTES: Typescript (photocopy) Thesis (Ph. D.)--Oregon State University, 1998. Includes bibliographical references (leaves 89-95).
SUBJECT: Truffles -- Washington (State) Forest thinning -- Washington (State) Hypogeous fungi -- Washington (State)

TITLE: Effect of mychorrhizae and rhizobacteria applications on plantlets development of forest species: Cordia alliodora and Tabebuia rosea.

AUTHOR: CUERVO, JAIRO
DEGREE: Magister Scientiae
YEAR: 1997
INSTITUTION: CENTRO AGRONOMICO TROPICAL DE INVESTIGACION Y ENSEÑANZA (CATIE) (Costa Rica)
ADVISER: GONZALO GALILEO RIVAS-PLATERO

The objective of this research was to increase Tabebuia rosea and Cordia alliodora growth at nursery level using for this purpose mychorrihizae. This research involved four experiments: 1) Use of Glomus occultum, (LOCT), Glomus manihotis (LMNH) and Entrophospora colombia (ECLB) mycorrhizae and the application of Bacillus cereus (Bc), Serratia marcescens (Sm) and Pseudomonas fluorescens (Pf) rhizobacteria, at the nursery stage of two forest species; 2) Identification of Bacillus serratia and Pseudomonas in soil samples where T. rosea and C. alliodora were growing; 3) Detection and quantification of mycorrhizae soil samples from several T. rosea and C. alliodora sites and 4) Use of organic fertilizers on soils with G. occultum at the nursery stage of T. rosea. The application of mycorrhizae fostered growth of T. rosea and C. alliodora plantlets. The variables height, leaves number, foliar area and dry weight, showed superior values than the control (p < 0.01). From all variables, LMNH presented the best results for T. rosea and ECLB for C. alliodora. The interaction mycorrhizae*rhizobacteria fostered plantlets development, but the values resulted were not superior to those obtained using only mycorrhizae inoculations. Furthermore, a higher number of spores was achieved as well as a higher percentage of mycorrhizae colonization. Soil samples obtained from places where T. rosea and C. alliodora grow presented chitinolytic, fluorescent and Gram negative bacteria as well as the mycorrhiza fungus Glomus and Gigaspora which have enormous research potential as growth promoters of these forest species. LOCT application in combination with organic fertilizers favored their own efficiency and promoted T. rosea growth. Organic fertilizers served as native mycorrhizae carriers; this condition makes them attractive for plants production.

Key words: mycorrhiza, rhizobacteria, Entrophospora colombiana, Glomus occultum, Glomus manihotis, Pseudomonas fluorescens, Serratia marcescens.

Gonzalo Galileo Rivas-Platero, M.Sc. Investigador

CATIE-Area de Agricultura Tropical Sostenible
7170 Turrialba, Costa Rica. C.A.
Tfno: (506) 556 0232 Ext. 391, 382
Fax : (506) 556 6480
Tfno (Habitación): (506) 556 1247
E-mail: grivas@computo.catie.ac.cr

ACCESSION NO.: AAG9824062
TITLE: ABSORBING SURFACE AREA OF SOUTHERN PINE ROOT SYSTEMS: PHOSPHORUS AND POTASSIUM UPTAKE BY ROOT SYSTEMS OF TWELVE-YEAR-OLD SLASH PINE TREES (HYPOXIC SOIL, PINUS ELLIOTTII)
AUTHOR: ESCAMILLA-BENCOMO, JOSE A.
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: UNIVERSITY OF FLORIDA; 0070
ADVISER: Chairman: NICHOLAS B. COMERFORD
SOURCE: DAI, VOL. 59-02B, Page 0476, 00158 Pages
DESCRIPTORS: AGRICULTURE, FORESTRY AND WILDLIFE; AGRICULTURE, PLANT PHYSIOLOGY
ABSTRACT: Our understanding of ion uptake by pine trees is principally based on studies of white roots of seedlings. However, root systems of trees consist of white, brown (woody and nonwoody) and mycorrhizal roots including external hyphae. It is unclear whether brown roots are functional in nutrient absorption. However, brown and woody roots may contribute over 80% of the fine-root system of slash pine (Pinus elliottii Engelm. var. elliotii). The aim of this research was to study P and K uptake by root systems of twelve-year-old slash pine growing under field conditions.

The first objective of my research was to develop a field method for measuring nutrient uptake by roots of trees. The design included (i) a root chamber, (ii) a system for controlling the O$sb2$ level of the root chamber, and (iii) a Mariotte flask system. The second objective was to (i) compare P and K depletion by lateral root systems of slash pine when the roots are subjected to a short-term, hypoxic treatment, and (ii) to document the ability of roots to absorb P and K following the removal of the hypoxic treatment.

N$sb2$ gas was used to achieve hypoxic conditions during the experiments $({<}50 mu$M O$sb2).$ Slash pine is grown extensively on soils where surface horizons are subject to short-term hypoxic conditions due to seasonal, fluctuating watertables. I demonstrated that that pine roots grown in aerobic soil conditions were capable of P uptake during short-duration hypoxic conditions. In contrast, K depletion was totally inhibited. Once the hypoxic condition was corrected, uptake of both P and K resumed.

The final objective of my research was to compare P and K influx rates between whole and woody roots of slash pine, while evaluating the mechanism of nutrient uptake by woody roots through the use of N$sb2$ gas as a metabolic inhibitor of ion absorption. I concluded that woody roots absorb P and K and that rates of ion uptake were similar to whole roots. I also documented an active K uptake mechanism by woody roots. The results indicated that estimates of the surface area of woody roots and sensitivity of K uptake under aerobic and hypoxic conditions, should be included in nutrient uptake models of slash pine ecosystems.

ACCESSION NO.: AAG9818802
TITLE: ADAPTATION RESPONSES OF TROPICAL FORAGE GRASS AND LEGUME SPECIES TO DEGRADED NUTRIENT-POOR ACID SOILS OF HILLSIDES AGROECOLOGICAL ZONE OF COLOMBIA
AUTHOR: GOMEZ-CARABALI, ARNULFO
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: NEW MEXICO STATE UNIVERSITY; 0143
ADVISER: Chair: RELDON F. BECK
SOURCE: DAI, VOL. 58-12B, Page 6289, 00211 Pages
DESCRIPTORS: AGRICULTURE, AGRONOMY; BIOLOGY, ECOLOGY
ABSTRACT: An evaluation (whether in monoculture or in mixture) of one C$sb4$ grass (Brachiaria dictyoneura) and two C$sb3$ tropical legumes (Arachis pintoi and Centrosema macrocarpum) under 2 fertilization levels was carried out. Adaptation responses of plant materials during the establishment period were measured in terms of their morphological, chemical and microbiological differences for above ground and below ground conditions.

Harvests were done at 16, 29, 38, and 55 weeks after planting. Also, an additional harvest was made after 6weeks of regrowth by mowing all plots at the end of the 55-week collection. Dry matter yield was closely related to fertilization level; thus the highest yield coincided with the higher fertilization rate. The grass B. dictyoneura alone recorded the highest dry matter yield followed by the two mixtures B. dictyoneura + C. macrocarpun and B. dictyoneura + A. pintoi which in turn were more productive than the legumes in monoculture and the native vegetation.

The growth analysis indicated that B. dictyoneura had the highest leaf area index at older stages and at high fertilization rates (6.61 at 38 weeks of age) and A. pintoi had the highest leaf area index at young stage of regrowth at high fertilization rate (2.76 at 6 weeks of regrowth). Leaf stem ratio was greater in the grass than in legumes and greater under the high fertilization rate.

Crude protein content and in vitro dry matter digestibility for either leaves or stems were higher at an early stage of regrowth than at an older age. The B. dictyoneura and the native vegetation had the lowest protein content, while the legumes C. macrocarpum and A. pintoi had highest protein content. A. pintoi had the lowest neutral and acid detergent fiber contents.

Mineral composition varied with time. P, Ca, and Mg decreased as the plants aged. The root study indicated that root length density and biomass production were higher at 0-10 cm depth than other depths at all ages. B. dictyoneura had the highest root length density at all depths and ages. While A. pintoi and C. macrocarpum, respectively, had lowest root length density. Nutrient acquisition and utilization measurements showed B. dictyoneura with the highest nutrient uptake and nutrient use efficiency of N and P. Slight increase in soil available P, Ca, Mg and S and a slight decrease in Al saturation as a result of fertilization was observed. Total soil N increased to about 700 ppm compared to the pre treatment status. All plant materials formed symbiotic relationships with mycorrhizal fugi. The numbers of spores in the soil and the percentage of infection of vesicular arbuscular mycorrhiza increased with age and varied with the species and season. (Abstract shortened by UMI.)

Harikumar, V.S. 1997. Endomycorrhizal Studies in Sweet Potato(Ipomoea batatas L.) Kerala University, Trivandrum, Kerala, India.

ACCESSION NO.: AAG9820297
TITLE: INSIGHTS INTO N DYNAMICS DURING SUCCESSION: LINKING ISOTOPIC EVIDENCE AND MODELING (PRIMARY SUCCESSION, NITROGEN DYNAMICS, ALASKA, ISOTOPIC SIGNATURES, ALNUS SINUATA)
AUTHOR: HOBBIE, ERIK ALAN
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: UNIVERSITY OF VIRGINIA; 0246
ADVISER: Advisers: HERMAN H. SHUGART; STEPHEN A. MACKO
SOURCE: DAI, VOL. 58-12B, Page 6354, 00159 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY; BIOGEOCHEMISTRY
ABSTRACT: The successional sequence of forests that have developed over the past 250 years at Glacier Bay, Alaska after glacial retreat are an ideal environment in which to study the development of nitrogen (N) dynamics. Nitrogen cycles rapidly during the early successional dominance of the N-fixing tree Alnus sinuata (Sitka alder) and cycles slowly during the late successional dominance of Picea sitchensis (Sitka spruce). Across sites representing different post-deglaciation ages, ecological parameters related to carbon (C) and nitrogen cycling were measured, with an emphasis on natural abundance isotopic measurements of soil, vegetation, and mycorrhizal fungi. To better understand the observed patterns, a computer model of N dynamics during succession was created (NIFTE: Nitrogen Isotope Fluxes in Terrestrial Ecosystems) and then used to test hypothesized relationships that guide ecosystem behavior. Comparison of initial model results with patterns of isotopic signatures led to the following hypotheses: (1) Spruce does not obtain most of its nitrogen directly from mineral N in the soil. (2) Mycorrhizae play an important role in transferring N to spruce. (3) Fractionating processes within mycorrhizae account for some isotopic patterns previously observed in ecosystem studies. (4) The contribution to the N budget of spruce by mycorrhizae increases in later succession with the decline in N availability and the increase in refractory pools of soil N.

A revised model incorporating these hypotheses reproduced the general patterns observed in fungi, plants, soil, and mineral N for isotopic results. Alternative explanations were also modeled for consistency with the data. The results suggested that modeling allows a more rigorous use of natural abundance measurements, which should increase the power of isotopic measurements to provide insight into N dynamics of terrestrial ecosystems. Negative correlations between C/N and $deltasp{15}$N in foliage at N-limited sites suggested that patterns of leaf nitrogen allocation were strongly influenced by the degree of mycorrhizal utilization for N supply on an evolutionary time-scale. Similar correlations within individual species across sites of differing nitrogen availabilities indicated the high plasticity of the mycorrhizal-plant interaction to environmental conditions, and its key role in regulating plant carbon and nitrogen balances.

ACCESSION NO.: AAG9803226
TITLE: THE BELOW GROUND VIEW OF ECTOMYCORRHIZAL FUNGI IN THREE CONIFER COMMUNITIES (PINUS MURICATA, PSEUDOTSUGA MENZIESII, PINUS RADIATA, RHIZOPOGON PARKSII, SUILLUS, AMANITA, RUSSULA BREVIPES, TUBER CALIFORNICUM)
AUTHOR: HORTON, THOMAS ROSCOE
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: UNIVERSITY OF CALIFORNIA, BERKELEY
ADVISER: Chair: THOMAS D. BRUNS
SOURCE: DAI, VOL. 58-08B, Page 4017, 00096 Pages
ABSTRACT: Ectomycorrhizal fungi of Pinus muricata (bishop pine), Pseudotsuga menziesii (Douglas-fir) and Pinus radiata (monterey pine) were investigated. Fungi were identified from field collected roots utilizing PCR based methods. The frequency and abundance of ectomycorrhizae were used to measure the contribution of each fungal species to ectomycorrhizal communities.

In the first study, a stand of bishop pine and Douglas- fir was investigated. The most frequent and abundant fungi in the stand were generalists. Twelve of sixteen fungi, making up 90% of the ectomycorrhizal biomass, associated with both hosts. Rhizopogon parksii was the only host specific fungus, associating with Douglas-fir. Three remaining species of fungi were too infrequent to assess their specificity. The results indicate that individual fungi may have linked the competing tree hosts below ground.

In the second study, first year bishop pine seedlings establishing after a wildfire were investigated. The frequency of seedlings colonized by fungi in burned ectomycorrhizal forest and burned VAM coastal scrub was compared. Seedlings from both locations were colonized by VAM, dark septate and ectomycorrhizal fungi. Seedlings in the scrub were only colonized by two Rhizopogon spp. and Suillus pungens. In contrast, a diverse group of ectomycorrhizal fungi colonized seedlings in the forest, including three Amanita spp., the two Rhizopogon spp. found in the scrub, Russula brevipes, Tuber californicum, and a cantharelloid species. The results indicate that most of the ectomycorrhizal fungi did not disperse into the area after the fire but were resident as spores in the scrub and spores and hyphae in the forest.

Finally, the ectomycorrhizal community of monterey pine plantations growing at about 3500 m in Salinas, Ecuador was investigated. Suillus luteus sporocarp production in these plantations was estimated to be over 100 kg ha$rmsp{-1} yrsp{-1},$ dry weight. Suillus luteus and T. terrestris were the only fungi observed as ectomycorrhizae in the plantations, each colonizing about 50% of the root tips down to 30 cm. These results indicate that the abnormally high S. luteus sporocarp production is correlated with, and may be a function of, a simplified ectomycorrhizal community in these plantations.

ACCESSION NO.: AAGMM16672
TITLE: GINSENG GARDEN FUMIGATION, AND PHOSPHATE EFFECTS ON THE MYCORRHIZAL ASSOCIATIONS OF AMERICAN GINSENG (PANAX QUINQUEFOLIUS L.)
AUTHOR: HOVIUS, JACOB PETER
DEGREE: M.SC.
YEAR: 1997
INSTITUTION: UNIVERSITY OF GUELPH (CANADA)
ADVISER: Adviser: R. L. PETERSON
SOURCE: MAI, VOL. 35-05, Page 1291, 00107 Pages
ISBN: 0-612-16672-4
ABSTRACT: The association between American ginseng grown in monoculture, and vesicular-arbuscular mycorrhizae (VAM) was investigated. Field fumigation significantly reduced soil levels of mycorrhizal fungal inoculum (MFI), whereas bed shaping had no effect on MFI levels across the bed width. Maximum percent ginseng root colonization was reached by mid-August for all plants with the exception of first-year plants growing in a second year garden, which increased until the end of the growing season. Arbuscular colonization peaked in August and was greater than hyphal colonization until mid-September. Plant growth did not always follow the same pattern of development for first and second-year plants, or between the 1995 and 1996 growing seasons, except for root to shoot ratios which increased over the entire season. Phosphate amendments had little direct effect on plant growth, but reduced VAM colonization by 10% at the highest phosphate level compared to the control. Differences in VAM colonization levels may have contributed to differences in plant growth.

ACCESSION NO.: AAG1386285
TITLE: THE EFFECT OF VARYING RATES OF METHAM AND APPLICATION METHOD ON PURPLE NUTSEDGE CONTROL AND COTTON VIGOR (CYPERUS ROTUNDUS)
AUTHOR: JIMENEZ, MANUEL REFUGIO
DEGREE: M.S.
YEAR: 1997
INSTITUTION: CALIFORNIA STATE UNIVERSITY, FRESNO; 6050
ADVISER: Chair: MAHLON M. S. HILE
SOURCE: MAI, VOL. 36-01, Page 0093, 00051 Pages
DESCRIPTORS: AGRICULTURE, AGRONOMY; AGRICULTURE, PLANT CULTURE
ABSTRACT: Metham applied with three different application methods at varying rates was investigated for control of Cyperus rotundus (purple nutsedge) and its effect on cotton vigor. Three rates of metham (25, 45, and 65 gallons per treated acre) were applied pre-plant using three different application methods: a single spray blade, a triple spray blade, and three-tiered fertilizer knives. Plots were arranged in a randomized complete block, with four replications. There were no significant differences in cotton plant density. Cotton seedlings from metham-treated soil were slightly taller than those grown in untreated soil. Metham reduced the severity of seedling disease. Mycorrhizal root infection and cotton seedling phosphate uptake were greatly reduced in all metham-treated plots. All metham treatments exhibited excellent control of purple nutsedge for 21 days (92 to 100% control). There were minor statistical differences in tuber counts among treatments. There were no significant differences among treatments in lint yield.

ACCESSION NO.: AAGC634437
TITLE: EFFECTS OF AIR POLLUTION AND FOREST REGENERATION METHODS ON THE COMMUNITY STRUCTURE OF ECTOMYCORRHIZAL FUNGI (PICEA ABIES, PINUS SYLVESTRIS, FERTILIZATION)
AUTHOR: KAREN, OLA
DEGREE: AGR.DR
YEAR: 1997
INSTITUTION: SVERIGES LANTBRUKSUNIVERSITET (SWEDEN); 0697
SOURCE: DAI, VOL. 59-02C, Page 0313, 00001 Pages
DESCRIPTORS: AGRICULTURE, FORESTRY AND WILDLIFE; AGRICULTURE, SOIL SCIENCE; BIOLOGY, MICROBIOLOGY; ENVIRONMENTAL SCIENCES; BIOLOGY, ECOLOGY
ISBN: 91-576-5317-8
PUBLISHER: SVERIGES LANTBRUKSUNIVERSITET, S-750 07 UPPSALA, SWEDEN
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: 37668688
AUTHOR: Kerbow, Dawn De.
TITLE: Some effects of soil on vesicular-arbuscular mycorrhizal fungal colonization and phosphorus accumulaltion in purple loosestrife (Lythrum Salicaria L.)
YEAR: 1997
PUB TYPE: Book
FORMAT: ix, 82 leaves, bound : col. map ; 28 cm.
NOTES: Thesis (M.S.)--University of Connecticut, 1997. Includes bibliographical references.

ACCESSION: 37270285
AUTHOR: Lerner, Jeffrey M., 1959-
TITLE: Mycorrhizal interactions of selected species of endangered New England flora
YEAR: 1997
PUB TYPE: Book
FORMAT: xviii, 209 leaves, bound : ill., maps ; 28 cm.
NOTES: Typescript. Thesis (M.S.)--University of Massachusetts at Amherst, 1997. Includes bibliographical references (leaves 191- 209).
SUBJECT: Endangered plants -- New England. Mycorrhizas -- New England. Plant diversity conservation -- New England.
ABSTRACT: Current strategies geared towards the preservation of floral biodiversity emphasize offsite propagation for the reestablishment of endangered plants. In this study a mycorrhizal inoculum containing a non-indigenous VAMF isolate (Glomus etunicatum) incorporated into a compost-based germination and transplant medium was effective at enhancing growth and transplant survival and reducing root disease (caused by soil-borne pathogens Rhizoctonia, Pythium, and Fusarium) in three (New England) endangered native species, including Gentianopsis crinita. These beneficial effects occurred without mycorrhizal colonization, indicating that they resulted from a suppressive microflora in the inoculum rather than mycorrhization of the plant host. In pathogen suppression and dilution and plating experiments this inoculum demonstrated a suppressive effect on soil microflora in general and on soil-borne fungal pathogens in particular. VA mycorrhizae, which first formed in G. crinita in late autumn, lasted throughout dormancy and were present at reemergence. The timing and morphology of mycorrhization in G. crinita indicate that it is a phenologically-based and functionally-defined symbiosis under the control of the gentian host. Mycorrhizae appear to play a role in the perennialization, dormancy, overwintering and reemergence of G. crinita. This study has demonstrated that VAM inoculum shows great potential as a biologically active pathogen-suppressant and plant enhancement agent in sustainable, ecologically-based horticultural production systems.

ACCESSION NO.: AAG9824518
TITLE: ARBUSCULAR MYCORRHIZAE ALTER INTRASPECIFIC COMPETITION
AUTHOR: MAFFIA, BLASE
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: UNIVERSITY OF MIAMI; 0125
ADVISER: Supervisor: DAVID P. JANOS
SOURCE: DAI, VOL. 59-02B, Page 0502, 00180 Pages
DESCRIPTORS: BIOLOGY, ECOLOGY; AGRICULTURE, PLANT PHYSIOLOGY; AGRICULTURE, PLANT CULTURE
ABSTRACT: By taking advantage of facultative mycotrophs' ability to grow with or without mycorrhizae at moderate soil nutrient levels, I investigated the role arbuscular mycorrhizae play in the growth, survivorship and size inequality development of even-aged monocultures (i.e., populations) of eight plant species grown over a range of densities. Mycorrhizae influence plant response to density in several ways. For Sunflower grown at very high density (160 plants/100 cm$sp2$), mycorrhizae reduced shoot biomass, but improved survival by delaying self-thinning. When grown at low density (23 plants/100 cm$sp2$) in a regular planting pattern, mycorrhizae retarded the growth of individuals in the large-size classes as compared to the large-size classes of controls grown without mycorrhizae. While hyphae may aid in the uptake of nutrients at a greater rate than control individuals of the same size, this uptake comes at the cost of photosynthate. This photosynthate cost decreases the overall competitive ability of large-sized individuals, and so results in reduced growth of individuals of large size. The net result is greater size uniformity in mycorrhizal populations than control populations. Species respond to mycorrhizae and density in a predictable fashion as shown by the six response types that I have recognized. Response type I plants exhibit a mycorrhiza growth advantage at low density going to mycorrhiza growth disadvantage at high density.

Response type II plants exhibit a mycorrhiza growth disadvantage at low density going to mycorrhiza growth advantage at high density. Response type III plants exhibit a consistent mycorrhiza advantage over the densities examined. Response type IV plants exhibit a consistent mycorrhiza disadvantage over the densities examined. Response type V plants exhibit no affect of mycorrhiza. Response type VI plants do not exhibit an affect of density. Response types demonstrate that the outcome of mycorrhiza and density interactions is dependent on the plant host-fungus-soil combination used.

Mycorrhizal impact on size inequality appears to be a function of size. Slopes of regression lines for mean shoot mass indicate that at high mean shoot mass, mycorrhizal populations exhibit smaller coefficients of variation and less skewing than for the control populations. Although species may respond to density and mycorrhizae with any of several response types, there seems to be a common, possibly allometrically-based plant size inequality response to mycorrhizae.

ACCESSION NO.: AAGNQ25119
TITLE: MOLECULAR IDENTIFICATION OF ERICOID MYCORRHIZAL FUNGI (GAULTHERIA SHALLON, OIDIODENDRON, HYMENOSCYPHUS)
AUTHOR: MONREAL, MARCIA AMELIA
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: THE UNIVERSITY OF BRITISH COLUMBIA (CANADA); 2500
ADVISER: Advisers: SHANNON BERCH; MARY BERBEE
SOURCE: DAI, VOL. 59-02B, Page 0534, 00130 Pages
DESCRIPTORS: BIOLOGY, MOLECULAR; BIOLOGY, BOTANY
ISBN: 0-612-25119-5
ABSTRACT: Molecular techniques facilitated the identification of ericoid mycorrhizal fungi associated with an ericaceous plant, salal (Gaultheria shallon Purch), dominant in some reforestation sites in the Canadian West Coast. The polymerase chain reaction (PCR) was used to amplify the DNA coding for the internal transcribed spacers (ITS1 and ITS2) of the nuclear ribosomal repeat of 28 fungal isolates. Restriction fragment length polymorphism (RFLP) patterns of these isolates obtained using a set of four restriction enzymes were compared and a synaptic key that differentiates these isolates into 14 groups was created. A fungal specific primer (ITS1-F) was used to amplify DNA of salal mycorrhizae obtained under axenic conditions with specific combinations of salal plants and fungal inoculum. Comparison among RFLP patterns of the fungal isolates with salal mycorhizae showed that the fungal specific primer (ITS1-F) allowed the preferential amplification of the fungal component of the mycorrhizal association. RFLPs of fungal isolates and salal mycorrhizae were identical. Mycorrhizal root fragments from a salal plant were collected at a reforestation site on Vancouver Island.

From one set of root fragments, DNA was extracted and amplified by PCR Subsequent RFLP patterns obtained indicated the presence of a selection of various fungi. A second set of 5 mm mycorrhizal roots fragments were plated on Petri dishes and 20 fungal isolates were obtained. The in vitro capacity to form mycorrhizae with salal was tested for all isolates and only five were confirmed mycorrhizal with salal. Known RFLP patterns were detected from two new isolates: one matched the RFLP pattern produced by Oidiodendron species and the other matched a nonsporulating fungus (Unknown 2) described from previous work. The RFLP patterns of the other 18 newly isolated sterile fungi, including three isolates that formed in vitro mycorrhizae with salal, were different from those of all known ericoid mycorrhizal fungi. The fifteen new isolates that did not form ericoid mycorrhizae in vitro corresponded with seven RFLP patterns and their roles in association with salal roots is unknown.

To create a method that would allow the direct assessment of the presence of known ericoid mycorrhizal fungi in salal roots collected from the field, the internal transcribed spacer ITS2 region and 3$spprime$ end of the 5.8S rRNA gene (400 base pairs) of 24 fungal isolates were amplified and sequenced. Sequence data analysis segregated the mycorrhizal isolates into two main groups, one including species of Oidiodendron, and the second including Hymenoscyphus and allied taxa.

Accordingly, three different specific primers were designed, the first to amplify Oidiodendron species, and the second and third, to identify clusters of isolates from the Hymenoscyphus group. Tests performed using the new primers with fungal DNA mixtures of known mycorrhizal isolates and non-mycorrhizal fungal isolates detected only the fungal DNA.

ACCESSION: 38913308
AUTHOR: Page, Jennifer Marie.
TITLE: The effects of habitat fragmentation on the mycorrhizal association of Phlox pilosa L., prairie phlox
YEAR: 1997
PUB TYPE: Book
FORMAT: vii, 58 leaves, bound ; 28 cm.
NOTES: Typescript (photocopy). Thesis (M.S.)--University of Iowa, 1997. Includes bibliographical references (leaves 52-58).

ACCESSION: 37477251
AUTHOR: Pratt, Heather A.
TITLE: Effects of flooding on mycorrhizae in cottonwoods and tamarisk in the Rio Grande Bosque
YEAR: 1997
PUB TYPE: Book
FORMAT: xi, 53 leaves : ill., map ; 29 cm.
NOTES: Thesis (M.S.)--University of New Mexico, 1997. Includes bibliographical references (leaves [19]- 26).
SUBJECT: Mycorrhizas. Plant-fungi relationships. Cottonwood -- Ecology. Tamarix -- Ecology.

ACCESSION NO.: AAG9802743
TITLE: ECOLOGY, PHYSIOLOGY AND GENETICS OF ZINC NUTRITION IN SRI LANKAN EXACUM HYBRIDS (GENTIANACEAE) (SRI LANKA, MYCORRHIZAE)
AUTHOR: RISEMAN, ANDREW LEE
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: THE PENNSYLVANIA STATE UNIVERSITY; 0176
ADVISER: Adviser: RICHARD CRAIG
SOURCE: DAI, VOL. 58-07B, Page 3395, 00152 Pages
DESCRIPTORS: AGRICULTURE, PLANT CULTURE; BIOLOGY, GENETICS; AGRICULTURE, PLANT PHYSIOLOGY; BIOLOGY, ECOLOGY
ABSTRACT: Exacum species native to the tropical island of Sri Lanka were collected and used as part of a breeding program at The Pennsylvania State University, U.S.A. Interspecific hybrids of these species display genotype specific zinc deficiency development under uniform environmental conditions. Three areas of research, ecological, physiological and genetic, were initiated to understand the development and exhibition of zinc deficiency in these plants. The ecological studies evaluated both the edaphic conditions of the native habitats of the species and the involvement of mycorrhizal formation as they affect zinc nutrition. The edaphic components which were determined to be significant in differentiating the species habitats were base saturation (Ca, Mg, and K content), zinc content and textural classification (sand, silt, and clay proportions). Using principal component analysis, these variables were able to distinguish 5 of the 6 species soil samples including samples from two sub-species, E. trinervium and E. ritigalensis. Exacum macranthum was not discernible from E. trinervium samples. In evaluating mycorrhizal formation, 9 interspecific accessions were inoculated with a single Glomus species. Hyphal growth was observed but no structures associated with a functional symbiosis or growth response was recorded.

The physiological investigations utilized two interspecific, clonaly propagated genotypes contrasting in zinc efficiency. No significant genotypic differences were observed for tissue zinc content or dry matter production under zinc stress, although the efficient genotype had higher mean value for dry matter production. Significant differences were identified for root to shoot ratio, root CEC, rhizosphere acidification, zinc uptake, and zinc translocation. The genetic studies utilized both hybrid progenies and self-pollinated progenies from the zinc efficient and zinc inefficient genotypes used in the physiological research. The hybrid progeny was used confirm the genetic basis of zinc efficiency and to evaluated parental contributions for specific deficiency symptoms. Deficiency symptom development was proven to be dependent on specific parental combination. The self-pollinated progeny were used to elucidate segregation patterns for physiological traits associated with zinc efficiency. Traits identified as important include zinc uptake on a root length basis, rhizosphere acidification, and specific root weight.

ACCESSION NO.: AAG9807487
TITLE: AN EXAMINATION OF THE INTERACTIONS BETWEEN GARLIC MUSTARD (ALLIARIA PETIOLATA (BEIB.) CAVARA & GRANDE) AND VESICULAR-ARBUSCULAR MYCORRHIZAL (VAM) FUNGI (GIGASPORA ROSEA)
AUTHOR: ROBERTS, KARL JOSEPH
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: ILLINOIS STATE UNIVERSITY
ADVISER: Chair: ROGER C. ANDERSON
SOURCE: DAI, VOL. 58-08B, Page 4021, 00087 Pages
ABSTRACT: In this study, I examined the mycorrhizal relationships of garlic mustard (Alliaria petiolata) in central Illinois, USA. Garlic mustard, an invasive nonmycorrhizal plant species, is naturalized in portions of the United States and Canada where it often displaces native herbaceous forest understory. I found little evidence for a direct effect of mycorrhizal fungi on the growth of garlic mustard. Total biomass production was not significantly different between plants grown in autoclaved soil with or without added vesicular- arbuscular mycorrhizal (VAM) fungal spores. However, garlic mustard root growth was reduced in the presence of VAM fungal inoculum. Root growth of garlic mustard was also less in nonautoclaved soil than in autoclaved soil. This difference may have been caused by greater competition from soil microbes for nutrients in nonautoclaved than autoclaved soil. Nevertheless, leachates of garlic mustard tissue suppressed spore germination of the VAM fungus Gigaspora rosea, depressed seed germination of tomato, and root growth of tomato and sorghum. When garlic mustard, mycorrhizal tomato, or no plants were grown in soil for sixty days, the decline in mycorrhizal inoculum potential (MIP) was significantly greater with garlic mustard than tomato. There was no significant difference in MIP decline between soil containing no plant or garlic mustard. There was a significant negative correlation between the density of garlic mustard plants in 10 cm x 10 cm quadrats, and the MIP of soil extracted from the upper 15 cm of soil within the quadrats. These results suggest that garlic mustard's success in invading forest understories where a high percentage (75%) of plant species are mycorrhizal may be partially due to its ability to interfere with the production of mycorrhizae.

ACCESSION NO.: AAGNQ25159
TITLE: PLANT GROWTH PROMOTING RHIZOBACTERIA (PGPR) FOR INTERIOR SPRUCE (PICEA ENGELMANNII X P. GLAUCA) SEEDLINGS (PICEA GLAUCA, MYCORRHIZAL FUNGI, BACILLUS, PSEUDOMONAS)
AUTHOR: SHISHIDO, MASAHIRO
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: THE UNIVERSITY OF BRITISH COLUMBIA (CANADA); 2500
ADVISER: Adviser: C. P. CHANWAY
SOURCE: DAI, VOL. 59-02B, Page 0521, 00324 Pages
DESCRIPTORS: BIOLOGY, MICROBIOLOGY; AGRICULTURE, FORESTRY AND WILDLIFE; AGRICULTURE, PLANT PHYSIOLOGY
ISBN: 0-612-25159-4
ABSTRACT: The relationship between interior spruce (Picea engelmannii Parry x P. glauca (Moench) Voss) and plant growth promoting rhizobacteria (PGPR) was studied under controlled environments and in the field. Large, statistically significant biomass increases were detected in spruce seedlings after PGPR inoculation, but seedling growth responses were variable. Co-adaptation involving host plants, PGPR and forest floor soils did not appear to explain such variability.

Synergistic effects of PGPR and mycorrhizal fungi on seedling growth were detected, but growth promotion also occurred in the absence of mycorrhizae, which suggests that bacteria x mycorrhizae interactions were unrelated to seedling growth response variability. PGPR colonization of seedling tissues was assessed using immunofluorescent microscopy and dilution plate counts.

When three Bacillus and three Pseudomonas strains were inoculated onto spruce seedling roots under gnotobiotic conditions, only Bacillus Pw2R and Pseudomonas Sm3RN were detected inside stem vascular tissues four months later. A field experiment was performed to evaluate differences in root colonization and seedling growth promotion between these endophytic and non-endophytic PGPR. Relative growth rates of spruce seedlings in the field suggested that once induced in the greenhouse, seedling growth promotion persisted under field conditions for at least four months. However, endophytic PGPR offered no apparent advantage over non-endophytes as growth promoters.

Mechanistic studies of plant growth promotion in sterile microcosms suggested that strains L6-16R, Pw2R, S20R, Sm3RN and Sw5RN did not depend on the presence of other deleterious microorganisms to promote seedling growth, but that strain Ss2RN might. However, addition of sterilized forest soil extracts facilitated seedling growth promotion by most PGPR. These results suggest that abiotic soil compounds may act as precursor substrates for PGPR production of plant growth stimulating substances, possibly, but not restricted to, phytohormones. Patchy distribution of such precursors in soil could cause seedling growth variability in response to PGPR inoculation. Finally, PGPR were observed to change soil microbial community population sizes and carbon substrate utilization patterns. Seedlings buffered these effects in only one of two forest soils evaluated, indicating that the origin of the soil microbial community is important in determining microfloral responses to PGPR introduction.

ACCESSION NO.: AAG9804339
TITLE: ASYMBIOTIC IN VITRO SEED GERMINATION, MICROPROPAGATION AND SCANNING ELECTRON MICROSCOPY OF SEVERAL TEMPERATE TERRESTRIAL ORCHIDS (ORCHIDACEAE)
AUTHOR: SZENDRAK, ERIKA
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: THE UNIVERSITY OF NEBRASKA - LINCOLN
ADVISER: Adviser: PAUL E. READ
SOURCE: DAI, VOL. 58-08B, Page 3987, 00213 Pages
ABSTRACT: Twenty-five different orchid species were successfully asymbiotically germinated and raised on a modified FAST medium (Fast, 1976; Szendrak and R. Eszeki, 1993). The development of germinating protocorms and young plantlets were recorded and compared among species. Spontaneous vegetative proliferation was also observed. Natural dispersed daylight and prevailing day-length were more favorable than 16-hour cool white fluorescent light for plantlet development. After two to three years of culture, the young plants were suitable for transfer ex vitro.

The effects of organic compounds most commonly used for orchid micropropagation (peptone, coconut water, casein+lactalbumin and glucose) and medium consistencies were investigated for the development of temperate orchid protocorms from five species. Medium consistency had an important role in protocorm proliferation and development. In most cases, the liquid medium increased proliferation and the size of the protocorms. The media supplemented with the undefined organic compounds led to a greater proliferation rate and larger protocorms than the medium supplemented with glucose. In general, peptone and coconut water resulted in best development and proliferation of protocorms, but this varied with species.

Anatomical structures and developmental patterns of seventeen temperate orchid species were observed by scanning electron microscopy (SEM). New information was recorded about the early stages of seed germination and protocorm development, the structural details of roots with mycorrhiza, stored materials (calcium oxalate crystals and starch), leaf/stem stomatal structure and anatomical details of the generative organs and ovule/seed development.

Extensive SEM observations were also conducted on the seeds of more than 120 temperate orchid species. The length of the smallest seeds was $sim$200 mm (Spiranthes spp.) and the largest ones reached $sim$1700 mm (Cypripedium, Epipactis spp.) in length. Both quantitative and qualitative data were collected and detailed descriptions of the seeds of the different orchids were prepared. Several fascinating surface patterns and shapes were found, which were specific not only on the level of higher taxonomic units, but sometimes were distinctive even for the species or subspecies.

ACCESSION NO.: AAG9803374
TITLE: THE EVOLUTION OF MYCO-HETEROTROPHY AND SPECIFICITY IN SOME NORTH AMERICAN ORCHIDS (ECTOMYCORRHIZAE, CORALLORHIZA, CEPHALANTHERA, EPIPARASITE)
AUTHOR: TAYLOR, DONALD LEE
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: UNIVERSITY OF CALIFORNIA, BERKELEY; 0028
ADVISER: Co-chairs: THOMAS D. BRUNS; JOHN W. TAYLOR
SOURCE: DAI, VOL. 58-07B, Page 3414, 00164 Pages
DESCRIPTORS: BIOLOGY, BOTANY; BIOLOGY, ECOLOGY; BIOLOGY, MICROBIOLOGY
ABSTRACT: North American nonphotosynthetic orchids were used to study the evolution of myco-heterotrophy. The goals were to determine the trophic niches of associated fungi, and to explore patterns of specialization in plant populations, species, and higher levels. DNA sequence based techniques allowed identification and phylogenetic analysis of the fungi. Typical orchids associate with free-living fungi which do not form mycorrhizae with other plants. In contrast, five Corallorhiza species and Cephalanthera austinae were associated with fungi which simultaneously formed ectomycorrhizae: these orchids are thus epiparasites. The myco-heterotroph, Hexalectris spicata, was associated primarily with fungi allied to the Sebacinaceae, which have unknown trophic niches.

Specialization in Cephalanthera and Corallorhiza was striking, compared to photosynthetic hosts of the same fungi. Each orchid species was associated with fungi from only one family. In the most specialized orchids, where associations were restricted to few species, the fungi belonged to tight clades within families. This clustering implies that plant targeting, rather that ecological pressures, control which fungal species colonize each orchid. Corallorhiza maculata had wider associations than its congeners, but many populations were restricted to one or a few fungal species. Habitat and orchid genotype were correlated with this population-level specialization in some cases. C. maculata and C. mertensiana were associated with fungi in overlapping clades, and yet never shared the same species, even when growing at the same site. The restricted associations of C. mertensiana were likely derived from C. maculata via narrowing of specificity. Published intra-generic relationships show that narrowing cannot explain specialization in all species, however. The closest photosynthetic relative of Corallorhiza, Oreorchis, had both ectomycorrhizal and free-living fungal associates, as did the distant relative Tipularia. However, evidence was found only for association with free-living fungi in the more basal, photsynthetic relatives Aplectrum and Cremastra. Therefore, at least one "jump" to associations with ectomycorrhizal fungi happened prior to the loss of photosynthesis in Corallorhiza. The switch to ectomycorrhizal fungal associations was a key event in the evolution of Corallorhiza, and was followed by striking, evolutionarily dynamic specialization similar to that of conventional parasite lineages.

ACCESSION: 38214234
AUTHOR: Terwilliger, John Robert.
TITLE: Small mammals, Ectomycorrhizae, and conifer succession in beaver meadows
YEAR: 1997
PUB TYPE: Book
FORMAT: vii, 65 leaves : ill. ; 28 cm.
SERIES: University of Minnesota, Duluth. Theses (Master).
NOTES: Computer printout. Thesis (M.S.)--University of Minnesota, 1997. Includes bibliographical references.
SUBJECT: Mammals -- Minnesota -- Habitat. Conifers -- Minnesota. Ectomycorrhizas -- Minnesota.

ACCESSION NO.: AAGNQ24787
TITLE: SOIL FERTILITY EFFECTS ON YIELD, PESTS, WEEDS AND SYMBIONTS OF FABABEAN (VICIA FABA L.) IN ECOLOGICAL FARMING SYSTEMS
AUTHOR: YANG, CHENGZHI
DEGREE: PH.D.
YEAR: 1997
INSTITUTION: DALHOUSIE UNIVERSITY (CANADA); 0328
ADVISER: Adviser: DAVID PATRIQUIN
SOURCE: DAI, VOL. 59-01B, Page 0003, 00203 Pages
DESCRIPTORS: AGRICULTURE, AGRONOMY; ENVIRONMENTAL SCIENCES
ISBN: 0-612-24787-2
ABSTRACT: Yield instability in fababean is a limitation to more widespread use of this potentially high yielding, N$sb2$-fixing crop. I hypothesized that high levels of residual N and P from other crops could reduce yields by stimulating pests, diseases, and weeds, and by suppressing rhizobial and mycorrhizal symbionts; also that deficiencies of K would increase susceptibility to pests and diseases. There were three components to the research: (1) A correlational study involving observations of soil and plant variables (yields, roots, symbionts, leaf nutrients) on manually weeded plots and unweeded plots was conducted on farmer-grown crops on 8 farms in Prince Edward Island (PEI). These farmers had eliminated or were reducing use of synthetic fertilizers and chemical controls of weeds, pests and diseases. (2) Prior to seeding fababean, N, P, K and Ca fertilizers were added to replicated plots on two farms in PEI (except for Ca) and two in Nova Scotia (NS) and to large concrete cylinders containing soils of low (LF) and high (HF) background fertility. All plots were weeded manually except at NS1 where non-weeded treatments were also included. Rock-P was included as an additional treatment in the cylinders. (3) Rhizobial and mycorrhizal isolates from each of two farms were inoculated individually and in different combinations onto plants grown on artificial medium in a growth chamber. Plant variables were observed in (2) and (3). Grain yields varied widely in the 8-farm study, and were highly correlated with leaf K, but not with nodulation, mycorrhizal levels or weeds. Positive responses to K were observed in the fertilizer experiments.

Adding N suppressed nodulation, but not yields. All fertilizers suppressed mycorrhizae at all sites except for N, P and K in the LF cylinders. Super-P increased nodulation and yield in the LF cylinders, but rock-P did not. At farm NS1, adding N increased losses of yield due to weeds. N increased levels of an insect pest in the HF but not in the LF cylinders. In the growth chamber experiments, inoculants that included mycorrhizae effected increases in grain + pod yield at levels of infection below those observed in the field. It is concluded that variation in soil K is a major factor in yield variation of fababean in PEI and NS. The critical and maximum normal leaf K levels appear to be higher than in other grain legumes. It is suggested that the high requirement for K is related to high yield and drought susceptibility of fababean. Nutrient suppression of mycorrhizal infection appears not to have negative effects on the crop, however complete elimination of mycorrhizae could have negative effects.