Fort Hood Military Reservation is a 900 km2 military installation located between Killeen, Copperas Cove, and Gatesville in central Texas. It supports two full armored divisions which require year-round, live-fire maneuvers and training (Ft. Hood, 2003). As a result of the constant foot traffic and use of heavy equipment, the soils on the training ranges have become increasingly compacted, eroded, and stripped of vegetation. This study evaluated the impact that selected soil amendments would have on soil aggregation, infiltration, and levels of glomalin. A field study was done on plots located inside Fort Hood on a Nuff silty clay (fine-silty, carbonatic, thermic Udic Calciustoll). The plots were amended with composted dairy manure, inorganic fertilizers, and native grass seed. Aggregate stability was determined using a wet sieving procedure and total glomalin values were quantified using a Bradford assay. Field measurements of infiltration rates were taken using a drip-type rainfall simulator. Aggregate stability exhibited decreased values over time for all treatments but two (Site Prep / No Seed and Site Prep / Compost / Seed). In addition, three treatments changed significantly over time (from before treatment application to after treatment application). These treatments were the Site Prep / Compost / No Seed, No Prep / No Seed, and No Prep / Seed treatments. Levels of glomalin increased significantly over time for all treatments (p-value <0.001). Glomalin was correlated to aggregate stability after treatments were applied (p-value <0.01) but not before (p-value 0.89). In addition, infiltration rates were not related to glomalin (p-value 0.9) or aggregate stability (p-value 0.09). Additional sampling of Fort Hood beyond the plot study demonstrates significant differences in aggregate stability, infiltration rates, and levels of glomalin. Measurements taken from ten sites showed no correlations between aggregate stability, infiltration rates, or glomalin. Organic C was correlated to percent water stable aggregates (%WSA) and levels of glomalin. These results illustrate the relationship between organic C and aggregate stability as well as glomalin levels in maintaining infiltration rates and reducing soil loss by erosion.

The thesis deals with quantitative characterization of glomaline in three localities (Hrušky, Bošovice and Zástřizly). We determine easily extractable glomalin by using Bradford´s method. We analyzed the dependence of glomaline on pH and physiological availability of soil nitrogen nitrogen (N/B). The glomalin content was relatively low but in view of the fact we analysed arable land it is standard. Furthermore we also reported that glomalin content was decreasing with soil depth. All these results correlate with other scientific publication. Our results show that glomalin content is one of the most sensitive biological parametr which response to soil disturbance.

This research is a two year study on the effects of endomycorrhizae on vegetable production using conventional vs. organic practices. Objective of this study was initiated to determine if mycorrhizae improve yield, available soil nutrients and soil quality from two different fertilizer sources. Measurements were taken on yield, available soil nutrients, and soil quality in comparison of glomalin production and soil loss percentage. Two plant species were chosen, Tomatoes (‘Big Beef’) and Bush Beans (‘Tenderette’). A randomized split block 2 x 3 factorial treatment arrangement was used with two crops and three different inputs: Mo- 0 mycorrhizae, M1- recommended rate, and M2- 2x recommended rate of mycorrhizae. Each mycorrhizal input was replicated three times in both the conventional and organic system. Results show there was no difference in yield based on mycorrhizae additions at any rate. There was a significant yield difference based on conventional production over organic production in tomatoes and snap beans in 2010 and tomatoes in 2011. Possible explanations for yield difference in the organic production system include: different insect controls and a slower release of nutrients from poultry litter. Available soil nutrients were not influenced in the study based on mycorrhizal inputs in inorganic or organic tomato production. Soil available nutrients were significantly influenced in organic tomato when compared to inorganic tomato production at selected sampling dates. Mycorrhizae did not influence soil fertility in inorganic snap bean or organic snap bean production. Soil available nutrients were significantly influenced in organic snap bean when compared to inorganic snap bean production at selected sampling dates. Glomalin production and soil loss percentage were not shown to be significantly different within organic or inorganic treatments based on mycorrhizae inputs. However, glomalin production was shown to be significantly greater in organic production compared to inorganic in 2011. An explanation of this could be due to the use of leaf mulch as organic weed control. Although a numerical decrease was observed in soil loss percentage in organic production compared to inorganic production from the first year to the second, it was not shown to be a significant amount.

Soil organic N (SON) comprises 90% of all N in surface soils, yet as much as half remains in forms which are chemically unknown or, at best, poorly understood. Analytical methods such has pyrolysis field-ionization mass spectrometry (Py-FIMS) and 15N cross polarization magic-angle spinning nuclear magnetic resonance (CPMAS-NMR) spectroscopy are widely used for the characterization of SON; however, these methods have limitations which contribute to the gaps in our understanding of SON chemistry. For example, Py-FIMS may produce heat-induced secondary compounds, and 15N-NMR may lack sensitivity and resolution for experiments at natural 15N abundance. X-ray absorption near edge structure (XANES) spectroscopy probes the bonding environment of individual elements. The application of this technique to complex environmental samples such as soil is still in its infancy, but early studies suggest that this technique may help resolve SON molecular structure. This dissertation sought to develop and apply synchrotron-based N and C K-edge XANES spectroscopy to the study of soil and soil extracts to determine the structures in which SON is bound. In these studies, Py-FIMS was coupled with XANES as a corroboratory technique.<p> Initial methodological development resulted in a calibration method whereby N2 gas generated in ammonium-containing salts was used to calibrate a soft X-ray beamline at the N K-edge. Although XANES can produce secondary compound artifacts, contrary to early assertions that it is a non-destructive technique, it was shown in a second study that beam-induced decomposition can be minimized by moving the beam to a fresh spot between scans.<p> Three applied studies exploring SON composition were conducted. These studies followed a spatial gradient ranging from the landscape scale, through a rhizosphere study, and ended with a study of glomalin-related soil protein (GRSP). Glomalin-related soil protein is a persistent soil glycoprotein of arbuscular mycorrhizal origin (AMF) implicated in aggregation and long-term C and N storage. Nitrogen and C K-edge XANES and Py-FIMS were used in all studies, and GRSP was further characterized using proteomics techniques.<p> Soil organic N composition was largely controlled by topographic position, and to a lesser degree, by cultivation. Divergent (i.e., water shedding) positions were enriched in carbohydrates and low molecular weight lignins, whereas convergent, depressional and level positions showed enrichment in lipid-type compounds. These differences were attributed to tillage-induced redistribution of soil, and water movement from upper to lower slope positions. Nitrogen XANES revealed a unique form of organic N, identified as N-bonded aromatics, particularly in the divergent positions.<p> Rhizosphere soil was enriched in higher molecular weight lipid-type materials and depleted in low molecular weight polar compounds. This was attributed to increased input of fresh plant material and higher microbial turnover in the rhizosphere. Nitrogen-bonded aromatics also were detected in the rhizosphere.<p> The GRSP extracts were characterized as mostly proteinaceous, but also contained many co-extracted, non-protein compounds. Despite being previously described as a glycoprotein, only weak carbohydrate signals were observed. Proteomics-based assessment of GRSP showed no homology to any proteins of AMF origin, instead showing homology with thioredoxin and with heat-stable soil proteins. This may be because protein databases do not yet contain glomalin-related sequences, or that glomalin is homologous to non-AMF soil proteins.<p> This dissertation demonstrated that N XANES is a sensitive and novel method for characterizing SON, and can be used complementarily with other analytical techniques such as Py-FIMS and proteomics. The continued development of XANES will provide a useful tool for SOM research into the future.

There is accumulating evidence that arbuscular mycorrhizal fungi (AMF) produce a glycoprotein called glomalin, which has the potential to increase soil carbon (C) and nitrogen (N) storage, thereby reducing soil emissions of carbon dioxide (CO2) and nitrous oxide (N2O) into the atmosphere. However, other soil microorganisms such as plant growth-promoting rhizobacteria (PGPR) that interact with AMF could indirectly influence glomalin production. The objectives of this study were to determine the effects of AMF and PGPR interactions on glomalin production and identify possible combinations of these organisms that could enhance C and N storage in the rhizosphere. The effects of AMF and PGPR interactions on pea (Pisum sativum L.) growth and correlations between glomalin production and plant growth also were assessed.<p> A series of growth chamber and laboratory experiments were conducted to examine the effect of fungal and host plant species on glomalin production by comparing the amounts of glomalin produced by Glomus clarum, G. intraradices, and G. mosseae in association with corn (Zea mays L.), in addition to examining differences in the ability of corn, pea, and wheat (Triticum aestivum L.) to support glomalin production by G. intraradices. There were no significant differences in glomalin production [measured in the rhizosphere as Bradford-reactive soil protein (BRSP)] by the three AMF species, whereas host plant significantly affected glomalin production. Specifically, higher BRSP concentrations were found in the rhizosphere of corn as compared to pea and wheat.<p> Additionally, the effect of long-term storage on the growth promoting traits of the PGPR strains selected; namely, Pseudomonas cepacia R55 and R85, P. aeruginosa R75, P. putida R105, and P. fluorescence R111 were investigated. These bacterial strains previously had been identified as PGPR, but had since undergone approximately twenty years of storage at -80¢ªC; thus, it was necessary to confirm that these strains had retained their plant growth promoting characteristics. Apparently, long-term storage had no significant adverse effect on the PGPR strains as all strains increased the total biomass of wheat significantly and demonstrated antagonism against fungal pathogens.<p> The possibility that spore-associated bacteria (SAB) could influence AMF associations, thereby affecting glomalin production, and subsequent crop yield potential was assessed. This was achieved by first isolating bacteria from disinfested spores of the AMF species and determining their potential as PGPR for wheat. According to fatty acid methyl ester (FAME) profiles, four genera of bacteria were isolated from AMF spores namely; Arthrobacter, Bacillus, Micrococcus, and Paenibacillus, of which Bacillus species were the most common SAB. None of these isolates, however, showed growth promoting abilities on wheat.<p> Based on the preliminary findings, the combined effects of the three AMF species and the five PGPR strains were examined on plant growth and glomalin production under gnotobiotic conditions using pea as the host plant. Interactions between G. intraradices and R75, R85, or R105 resulted in increased BRSP concentration in the mycorrhizosphere of pea. Additionally, significant interactions were observed between the AMF species and PGPR strains on BRSP concentration in pea rhizosphere under non-sterile conditions. As observed under sterile conditions, the co-inoculation of pea with G. intraradices and R75 or R85 increased BRSP concentrations in the rhizosphere of pea grown in non-sterile soil, although interaction effects were not significantly different from the control or when G. intraradices was applied alone. Significant AMF and PGPR interactions were observed to affect AMF colonization; however, the combination of these organisms did not significantly affect pea growth, nutrient uptake, and C and N storage in the plant rhizosphere. No correlations were detected between glomalin-related soil protein (GRSP), pea growth, nutrient concentrations in the plant tissue, and soil organic C and N content. This study demonstrated that although the potential exists to manipulate certain AMF and PGPR to enhance glomalin production, co-inoculation of AMF and PGPR did not enhance plant growth or C and N storage beyond that achieved by inoculation of either organism.

Soil organic N (SON) comprises 90% of all N in surface soils, yet as much as half remains in forms which are chemically unknown or, at best, poorly understood. Analytical methods such has pyrolysis field-ionization mass spectrometry (Py-FIMS) and 15N cross polarization magic-angle spinning nuclear magnetic resonance (CPMAS-NMR) spectroscopy are widely used for the characterization of SON; however, these methods have limitations which contribute to the gaps in our understanding of SON chemistry. For example, Py-FIMS may produce heat-induced secondary compounds, and 15N-NMR may lack sensitivity and resolution for experiments at natural 15N abundance. X-ray absorption near edge structure (XANES) spectroscopy probes the bonding environment of individual elements. The application of this technique to complex environmental samples such as soil is still in its infancy, but early studies suggest that this technique may help resolve SON molecular structure. This dissertation sought to develop and apply synchrotron-based N and C K-edge XANES spectroscopy to the study of soil and soil extracts to determine the structures in which SON is bound. In these studies, Py-FIMS was coupled with XANES as a corroboratory technique.<p> Initial methodological development resulted in a calibration method whereby N2 gas generated in ammonium-containing salts was used to calibrate a soft X-ray beamline at the N K-edge. Although XANES can produce secondary compound artifacts, contrary to early assertions that it is a non-destructive technique, it was shown in a second study that beam-induced decomposition can be minimized by moving the beam to a fresh spot between scans.<p> Three applied studies exploring SON composition were conducted. These studies followed a spatial gradient ranging from the landscape scale, through a rhizosphere study, and ended with a study of glomalin-related soil protein (GRSP). Glomalin-related soil protein is a persistent soil glycoprotein of arbuscular mycorrhizal origin (AMF) implicated in aggregation and long-term C and N storage. Nitrogen and C K-edge XANES and Py-FIMS were used in all studies, and GRSP was further characterized using proteomics techniques.<p> Soil organic N composition was largely controlled by topographic position, and to a lesser degree, by cultivation. Divergent (i.e., water shedding) positions were enriched in carbohydrates and low molecular weight lignins, whereas convergent, depressional and level positions showed enrichment in lipid-type compounds. These differences were attributed to tillage-induced redistribution of soil, and water movement from upper to lower slope positions. Nitrogen XANES revealed a unique form of organic N, identified as N-bonded aromatics, particularly in the divergent positions.<p> Rhizosphere soil was enriched in higher molecular weight lipid-type materials and depleted in low molecular weight polar compounds. This was attributed to increased input of fresh plant material and higher microbial turnover in the rhizosphere. Nitrogen-bonded aromatics also were detected in the rhizosphere.<p> The GRSP extracts were characterized as mostly proteinaceous, but also contained many co-extracted, non-protein compounds. Despite being previously described as a glycoprotein, only weak carbohydrate signals were observed. Proteomics-based assessment of GRSP showed no homology to any proteins of AMF origin, instead showing homology with thioredoxin and with heat-stable soil proteins. This may be because protein databases do not yet contain glomalin-related sequences, or that glomalin is homologous to non-AMF soil proteins.<p> This dissertation demonstrated that N XANES is a sensitive and novel method for characterizing SON, and can be used complementarily with other analytical techniques such as Py-FIMS and proteomics. The continued development of XANES will provide a useful tool for SOM research into the future.

There is accumulating evidence that arbuscular mycorrhizal fungi (AMF) produce a glycoprotein called glomalin, which has the potential to increase soil carbon (C) and nitrogen (N) storage, thereby reducing soil emissions of carbon dioxide (CO2) and nitrous oxide (N2O) into the atmosphere. However, other soil microorganisms such as plant growth-promoting rhizobacteria (PGPR) that interact with AMF could indirectly influence glomalin production. The objectives of this study were to determine the effects of AMF and PGPR interactions on glomalin production and identify possible combinations of these organisms that could enhance C and N storage in the rhizosphere. The effects of AMF and PGPR interactions on pea (Pisum sativum L.) growth and correlations between glomalin production and plant growth also were assessed.<p> A series of growth chamber and laboratory experiments were conducted to examine the effect of fungal and host plant species on glomalin production by comparing the amounts of glomalin produced by Glomus clarum, G. intraradices, and G. mosseae in association with corn (Zea mays L.), in addition to examining differences in the ability of corn, pea, and wheat (Triticum aestivum L.) to support glomalin production by G. intraradices. There were no significant differences in glomalin production [measured in the rhizosphere as Bradford-reactive soil protein (BRSP)] by the three AMF species, whereas host plant significantly affected glomalin production. Specifically, higher BRSP concentrations were found in the rhizosphere of corn as compared to pea and wheat.<p> Additionally, the effect of long-term storage on the growth promoting traits of the PGPR strains selected; namely, Pseudomonas cepacia R55 and R85, P. aeruginosa R75, P. putida R105, and P. fluorescence R111 were investigated. These bacterial strains previously had been identified as PGPR, but had since undergone approximately twenty years of storage at -80¢ªC; thus, it was necessary to confirm that these strains had retained their plant growth promoting characteristics. Apparently, long-term storage had no significant adverse effect on the PGPR strains as all strains increased the total biomass of wheat significantly and demonstrated antagonism against fungal pathogens.<p> The possibility that spore-associated bacteria (SAB) could influence AMF associations, thereby affecting glomalin production, and subsequent crop yield potential was assessed. This was achieved by first isolating bacteria from disinfested spores of the AMF species and determining their potential as PGPR for wheat. According to fatty acid methyl ester (FAME) profiles, four genera of bacteria were isolated from AMF spores namely; Arthrobacter, Bacillus, Micrococcus, and Paenibacillus, of which Bacillus species were the most common SAB. None of these isolates, however, showed growth promoting abilities on wheat.<p> Based on the preliminary findings, the combined effects of the three AMF species and the five PGPR strains were examined on plant growth and glomalin production under gnotobiotic conditions using pea as the host plant. Interactions between G. intraradices and R75, R85, or R105 resulted in increased BRSP concentration in the mycorrhizosphere of pea. Additionally, significant interactions were observed between the AMF species and PGPR strains on BRSP concentration in pea rhizosphere under non-sterile conditions. As observed under sterile conditions, the co-inoculation of pea with G. intraradices and R75 or R85 increased BRSP concentrations in the rhizosphere of pea grown in non-sterile soil, although interaction effects were not significantly different from the control or when G. intraradices was applied alone. Significant AMF and PGPR interactions were observed to affect AMF colonization; however, the combination of these organisms did not significantly affect pea growth, nutrient uptake, and C and N storage in the plant rhizosphere. No correlations were detected between glomalin-related soil protein (GRSP), pea growth, nutrient concentrations in the plant tissue, and soil organic C and N content. This study demonstrated that although the potential exists to manipulate certain AMF and PGPR to enhance glomalin production, co-inoculation of AMF and PGPR did not enhance plant growth or C and N storage beyond that achieved by inoculation of either organism.

Made available in DSpace on 2016-04-28T14:58:36Z (GMT). No. of bitstreams: 1 2008 - Diego Campana Loureiro.pdf: 2157788 bytes, checksum: f03d9840bbd1a3cb93e49a59ea0309a6 (MD5) Previous issue date: 2008-02-27 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The objective of this work was to study the spatial variability of microbial biomass (BMS) and labile soil organic matter pools (MOS), under different systems of management and plant cover. The experiment was conducted in a Haplic Planosol soil on an Integrated Agroecological Production System (SIPA) at Embrapa Agrobiology Center/UFRRJ/Pesagro, Serop?dica, Rio de Janeiro. The evaluated management systems were: alley cropping, pasture, and forest garden as a reference area. It was used as sampling system three grids of regular spacing of 2.5 meters, consisting of 25 georeferentiated points, where soil samples at 10cm depth were taken. The following labile constituents were determined: free light fraction (FLL), water soluble C and N, C and N of BMS, and glomalin content. The areas of alley cropping and pasture showed spatial dependence to the attributes of MOS. The occurrence of larger spatial dependence of the parameters associated to microbial biomass in the alley cropping system (Corg, FLL, BMS-N and respiration), probably was due to external factors related to management, such as: intensive rotational cropping system, diversity of cultures and different inputs of organic matter to soil (pruning material and organic compost). / O objetivo do trabalho foi estudar a variabilidade espacial da biomassa microbiana (BMS) e os constituintes l?beis da mat?ria org?nica do solo (MOS), sob diferentes sistemas de manejo e cobertura vegetal. O experimento foi instalado em um Planossolo H?plico no Sistema Integrado de Produ??o Agroecol?gica (SIPA) da Embrapa Agrobiologia/UFRRJ/Pesagro, Serop?dica/RJ. Os sistemas de manejo avaliados foram: cultivo em al?ias, pastagem e horto florestal como ?rea de refer?ncia. Para a amostragem utilizou-se 3 grades regulares com espa?amento de 2,5 metros, composta de 25 pontos georreferenciados para cada grade, onde coletou-se amostras de solo na profundidade de 0-10 cm. Em cada amostra determinou-se os teores de C e N associados ? BMS e os seguintes constituintes l?beis da MOS: fra??o leve livre, formas de C e N sol?veis em ?gua e teor de glomalina. Determinaram-se tamb?m as fra??es granulom?tricas areia, silte, argila, umidade gravim?trica, bem como os atributos qu?micos c?lcio, magn?sio, f?sforo, pot?ssio, carbono org?nico, nitrog?nio total, alum?nio, CTC e pH em ?gua. Somente as ?reas de cultivo em al?ias e pastagem apresentaram depend?ncia espacial para os atributos da MOS. A ocorr?ncia de maior depend?ncia espacial dos par?metros associados ? BMS nas al?ias (Corg, fra??o leve livre da MO, BMS-N e respira??o) deveu-se provavelmente a fatores extr?nsecos relacionados ao manejo, tais como: intensa rota??o e diversidade de culturas e aporte diferenciado de adubos org?nicos (material de poda e aplica??o de compostos org?nicos).

La germination des spores est une étape essentielle dans le cycle de vie de la majorité des champignons filamenteux. Les champignons mycorhiziens à arbuscules (CMA) forment un certain nombre de propagules infectieuses différentes qui augmentent leur potentiel à coloniser les racines. Parmi elles se trouvent les spores extraracinaires et intraracinaires. La paroi cellulaire des spores joue un rôle majeur dans la survie de ces propagules en étant une barrière physique et osmotique. Puisque une cellule peut faire des ajustements considérables dans la composition et la structure de sa paroi, en réponse aux conditions environnementales, il est possible que les parois des spores intraracinaires et extraracinaires montrent des propriétés mécaniques et osmotiques différentes affectant leur germination et leur survie. Pourtant, contrairement à la connaissance de la génétique moléculaire et de la formation de la paroi cellulaire des CMA, peu d’information est disponible au sujet de ces propriétés mécaniques. Les informations sur la germination des CMA dans des conditions hypertoniques sont aussi rares, et les modèles expérimentaux ne séparent généralement pas les effets directs de la forte pression osmotique externe sur la germination des champignons et les effets attribuables aux plantes. Cette étude avait pour but de répondre à deux importantes séries de questions concernant le comportement des spores mycorhiziennes. Nous avons d'abord déterminé la relation entre la composition de la paroi cellulaire, la structure et les propriétés mécaniques du champignon modèle Glomus irregulare (isolat DAOM 197198). La micro-indentation a été utilisée pour mesurer quantitativement les propriétés mécaniques de la paroi cellulaire. La composition (contenu de chitine et de glomaline) de la paroi cellulaire a été quantifiée par immunofluorescence tandis que la microscopie optique a été utilisée pour mesurer l'épaisseur de la paroi cellulaire. La densité locale en glomaline et l’épaisseur de la paroi étaient significativement plus élevées pour les parois des spores extraracinaires alors que la densité locale en chitine et la rigidité n’ont pas montré de variations entre les spores extraracinaires et intraracinaires. La grande variabilité dans les paramètres étudiés nous a empêchés de cibler un facteur principal responsable de la force totale de la paroi lors de la compression. La diminution des concentrations de chitine et de glomaline a été corrélée à l'évolution de la paroi du champignon au cours de son cycle de vie. On a aussi observé une composition différentielle des couches de la paroi: les polymères de chitine et de glomaline furent localisés principalement dans les couches externes et internes de la paroi, respectivement. Dans la deuxième partie de notre travail, nous avons exploré les effets directs d'engrais, par rapport à leur activité de l'eau (aw), sur la germination des spores et la pression de turgescence cellulaire. Les spores ont été soumises à trois engrais avec des valeurs de aw différentes et la germination ainsi que la cytorrhyse (effondrement de la paroi cellulaire) des spores ont été évaluées après différents temps d'incubation. Les valeurs de aw des engrais ont été utilisées comme indicateurs de leurs pressions osmotiques. L'exposition des spores de Glomus irregulare au choc osmotique causé par les engrais dont les valeurs de aw se situent entre 0,982 et 0,882 a provoqué des changements graduels au niveau de leur cytorrhyse et de leur germination. Avec l'augmentation de la pression de turgescence externe, la cytorrhyse a augmenté, tandis que le taux de germination a diminué. Ces effets ont été plus prononcés à des concentrations élevées en éléments nutritifs. La présente étude, bien qu’elle constitue une étape importante dans la compréhension des propriétés mécaniques et osmotiques des spores de CMA, confirme également que ces propriétés dépendent probablement de plusieurs facteurs, dont certains qui ne sont pas encore identifiés. / Spore germination is an essential developmental stage in the life cycle of many filamentous fungi. Arbuscular mycorrhizal fungi (AMF) form a number of different infectious propagules that increase their potential to colonize roots. Among them are extraradical and intraradical spores. The spore cell wall plays a major role in the survival of these propagules by being a physical and osmotic barrier. Because a cell can make considerable adjustments to the composition and structure of its wall in response to environmental conditions, it is possible that intraradical and extraradical spore walls show different mechanical and osmotic properties affecting their survival and germination. However, in contrast to the knowledge on the genetics and molecular composition of AMF cell wall, little is known about its mechanical properties. Information on the germination of AMF under hypertonic conditions is scarce, and experimental designs and methodologies have generally not allowed the direct effects of high external osmotic pressure on fungal germination to be separated from plant-mediated effects. This study had the goal to address two important sets of questions regarding the behavior of mycorrhizal spores. We first determined the relationship between cell wall composition, structure and mechanical properties of the model fungus Glomus irregulare. Micro-indentation was used to quantitatively measure the cell wall mechanical properties. Cell wall composition (chitin and glomalin content) was studied by immunofluorescence whereas optical microscopy was used to measure the cell wall thickness. Glomalin local density and wall thickness were both significantly higher for extraradical spore walls while chitin local density and rigidity were unaffected by origin of spores. High variability in results prevented us from identifying a primary factor responsible for overall wall strength during compression. Decreases of chitin and glomalin concentrations were correlated to the development of the fungal wall throughout its life-cycle. There was also differential association within the wall layers: The chitin and glomalin polymers were localized mostly in the outer and inner walls, respectively. In the second part of our work, we explored the direct effects of fertilizers, in relation to their water activity (aw), on spore germination and cellular turgor pressure. Spores were exposed to three fertilizers with different aw and spore germination and cytorrhysis of spores were assessed after different times of incubation. Water activities of the fertilizers were used as indicators of their osmotic pressures. Osmotic shock exposure of the Glomus irregulare spores to fertilizers at aw values between 0.982 and 0.882 caused gradual changes in cytorrhysis and germination. With the increase of external turgor pressure, cytorrhysis increased while the rate of germination decreased. These effects were most pronounced at high nutrient concentrations. The present investigation, while likely representing a significant step forward in understanding the mechanical and osmotic properties of AMF spores, also confirms that they might depend on many, as yet unidentified factors. Future research should examine differences in the physiology to discern reasons for such differences in spore properties.

La germination des spores est une étape essentielle dans le cycle de vie de la majorité des champignons filamenteux. Les champignons mycorhiziens à arbuscules (CMA) forment un certain nombre de propagules infectieuses différentes qui augmentent leur potentiel à coloniser les racines. Parmi elles se trouvent les spores extraracinaires et intraracinaires. La paroi cellulaire des spores joue un rôle majeur dans la survie de ces propagules en étant une barrière physique et osmotique. Puisque une cellule peut faire des ajustements considérables dans la composition et la structure de sa paroi, en réponse aux conditions environnementales, il est possible que les parois des spores intraracinaires et extraracinaires montrent des propriétés mécaniques et osmotiques différentes affectant leur germination et leur survie. Pourtant, contrairement à la connaissance de la génétique moléculaire et de la formation de la paroi cellulaire des CMA, peu d’information est disponible au sujet de ces propriétés mécaniques. Les informations sur la germination des CMA dans des conditions hypertoniques sont aussi rares, et les modèles expérimentaux ne séparent généralement pas les effets directs de la forte pression osmotique externe sur la germination des champignons et les effets attribuables aux plantes. Cette étude avait pour but de répondre à deux importantes séries de questions concernant le comportement des spores mycorhiziennes. Nous avons d'abord déterminé la relation entre la composition de la paroi cellulaire, la structure et les propriétés mécaniques du champignon modèle Glomus irregulare (isolat DAOM 197198). La micro-indentation a été utilisée pour mesurer quantitativement les propriétés mécaniques de la paroi cellulaire. La composition (contenu de chitine et de glomaline) de la paroi cellulaire a été quantifiée par immunofluorescence tandis que la microscopie optique a été utilisée pour mesurer l'épaisseur de la paroi cellulaire. La densité locale en glomaline et l’épaisseur de la paroi étaient significativement plus élevées pour les parois des spores extraracinaires alors que la densité locale en chitine et la rigidité n’ont pas montré de variations entre les spores extraracinaires et intraracinaires. La grande variabilité dans les paramètres étudiés nous a empêchés de cibler un facteur principal responsable de la force totale de la paroi lors de la compression. La diminution des concentrations de chitine et de glomaline a été corrélée à l'évolution de la paroi du champignon au cours de son cycle de vie. On a aussi observé une composition différentielle des couches de la paroi: les polymères de chitine et de glomaline furent localisés principalement dans les couches externes et internes de la paroi, respectivement. Dans la deuxième partie de notre travail, nous avons exploré les effets directs d'engrais, par rapport à leur activité de l'eau (aw), sur la germination des spores et la pression de turgescence cellulaire. Les spores ont été soumises à trois engrais avec des valeurs de aw différentes et la germination ainsi que la cytorrhyse (effondrement de la paroi cellulaire) des spores ont été évaluées après différents temps d'incubation. Les valeurs de aw des engrais ont été utilisées comme indicateurs de leurs pressions osmotiques. L'exposition des spores de Glomus irregulare au choc osmotique causé par les engrais dont les valeurs de aw se situent entre 0,982 et 0,882 a provoqué des changements graduels au niveau de leur cytorrhyse et de leur germination. Avec l'augmentation de la pression de turgescence externe, la cytorrhyse a augmenté, tandis que le taux de germination a diminué. Ces effets ont été plus prononcés à des concentrations élevées en éléments nutritifs. La présente étude, bien qu’elle constitue une étape importante dans la compréhension des propriétés mécaniques et osmotiques des spores de CMA, confirme également que ces propriétés dépendent probablement de plusieurs facteurs, dont certains qui ne sont pas encore identifiés. / Spore germination is an essential developmental stage in the life cycle of many filamentous fungi. Arbuscular mycorrhizal fungi (AMF) form a number of different infectious propagules that increase their potential to colonize roots. Among them are extraradical and intraradical spores. The spore cell wall plays a major role in the survival of these propagules by being a physical and osmotic barrier. Because a cell can make considerable adjustments to the composition and structure of its wall in response to environmental conditions, it is possible that intraradical and extraradical spore walls show different mechanical and osmotic properties affecting their survival and germination. However, in contrast to the knowledge on the genetics and molecular composition of AMF cell wall, little is known about its mechanical properties. Information on the germination of AMF under hypertonic conditions is scarce, and experimental designs and methodologies have generally not allowed the direct effects of high external osmotic pressure on fungal germination to be separated from plant-mediated effects. This study had the goal to address two important sets of questions regarding the behavior of mycorrhizal spores. We first determined the relationship between cell wall composition, structure and mechanical properties of the model fungus Glomus irregulare. Micro-indentation was used to quantitatively measure the cell wall mechanical properties. Cell wall composition (chitin and glomalin content) was studied by immunofluorescence whereas optical microscopy was used to measure the cell wall thickness. Glomalin local density and wall thickness were both significantly higher for extraradical spore walls while chitin local density and rigidity were unaffected by origin of spores. High variability in results prevented us from identifying a primary factor responsible for overall wall strength during compression. Decreases of chitin and glomalin concentrations were correlated to the development of the fungal wall throughout its life-cycle. There was also differential association within the wall layers: The chitin and glomalin polymers were localized mostly in the outer and inner walls, respectively. In the second part of our work, we explored the direct effects of fertilizers, in relation to their water activity (aw), on spore germination and cellular turgor pressure. Spores were exposed to three fertilizers with different aw and spore germination and cytorrhysis of spores were assessed after different times of incubation. Water activities of the fertilizers were used as indicators of their osmotic pressures. Osmotic shock exposure of the Glomus irregulare spores to fertilizers at aw values between 0.982 and 0.882 caused gradual changes in cytorrhysis and germination. With the increase of external turgor pressure, cytorrhysis increased while the rate of germination decreased. These effects were most pronounced at high nutrient concentrations. The present investigation, while likely representing a significant step forward in understanding the mechanical and osmotic properties of AMF spores, also confirms that they might depend on many, as yet unidentified factors. Future research should examine differences in the physiology to discern reasons for such differences in spore properties.