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Symbiotic associations with arbuscular mycorrhizal fungi (AMF) offer an effective indirect mechanism to reduce heavy metal (HM) stress; however, it is still not clear which AMF species are more efficient as bioremediating agents. We selected different species of AMF: Rhizoglomus custos (Custos); Rhizoglomus sp. (Aznalcollar); and Rhizophagus irregularis (Intraradices), in order to study their inoculation in wheat grown in two soils contaminated with two levels of HMs; we tested the phytoprotection potential of the different AMF symbioses, as well as the physiological responses of the plants to HM stress. Plants inoculated with indigenous Aznalcollar fungus exhibited higher levels of accumulation, mainly in the shoots of most of the HM analyzed in heavily contaminated soil. However, the plants inoculated with the non-indigenous Custos and Intraradices showed depletion of some of the HM. In the less-contaminated soil, the Custos and Intraradices fungi exhibited the greatest bioaccumulation capacity. Interestingly, soil enzymatic activity and the enzymatic antioxidant systems of the plant increased in all AMF treatments tested in the soils with both degrees of contamination. Our results highlight the different AMF strategies with similar effectiveness, whereby Aznalcollar improves phytoremediation, while both Custos and Intraradices enhance the bioprotection of wheat in HM-contaminated environments.

Emerging insights on the role of microbiomes in the sustainability of ecosystems and plant cover are transforming knowledge-driven agro-environmental management practices. For more than a century, the Brazilian pepper tree -BP (Schinus terebinthifolius), a category 1 invasive plant in Florida has defied numerous conventional control measures directed at its well-known ecology. This dissertation is one of the pioneer studies designed to determine whether microorganisms play a role in the aggressive invasion of BP in Florida and examine potential mechanisms with the goal of creating supplemental restoration tools. To test the hypothesis that enhanced mutualism of Brazilian pepper tree with microbes, compounded by relatively low biotic resistance of Florida soils is a critical driver of its invasion, plant biomass indices, metagenomics analysis of microbial community shifts, electron microscopy of endomycorrhizal infection and qPCR of key rhizobacterial taxa were measured. A multifactorial grow-room experiment was conducted simulating invasion with BP and two Florida natives (Pinus elliottii and Bidens alba) in a sterile, bioinoculant supplemented, and non-sterile control soils with various plant combinations., 2022, Includes bibliography., Degree granted: Dissertation (Ph.D.)--Florida Atlantic University, 2022., Collection: FAU Electronic Theses and Dissertations Collection

Arbuscular mycorrhizas (AM) are mutualistic symbioses occurring between the vast majority of land plant roots and a reduced group of soilborne fungi, the arbuscular mycorrhizal fungi (AMF). The fungus provides the plant of water and mineral and organic nutrients acquired very efficiently from the soil via fungal hyphae, which enhances plant nutritional status and physiological equilibrium, and results in higher yield and a healthier and more sustainable crop production. However, the obligate biotrophic status of AMF has hampered up to recently the large-scale production and application of AMF as inoculants. Conventional AMF inoculants consist of solid grain or powder substrates mainly containing dormant fungal spores, usually in a too-low percentage and often difficult to detect and verify for their vitality. These inoculants are difficult to apply homogeneously via watering systems, slow to establish symbiosis and, what is worst, usually contain non-desired microorganisms, due to their non-in vitro production and formulation. This situation gave a U-turn ten years ago with the presentation of the first ultrapure, gel-type mycorrhizal inoculant in the world, MYCOGEL®, produced and commercialized in vitro to preserve all its quality and traceability from the lab to the field. MYCOGEL® promotes a very quick and specific AM response to the plant, thus exerting all AM benefits from the beginning of its lifespan, to finally enhance fruit production in terms of amount and quality. In this paper we present the first results obtained in Japan on MYCOGEL® application to different crops in agronomic conditions. Rice, green onion, lettuce, tomato, onion, green pepper, celery and grape were the crops tested, with important increases in crop productivity, quality and yield value. The relative importance of the percentage of mycorrhizal colonization of the roots vs. the agronomic effects observed is also discussed.

Substantial amounts of nutrients are lost from soils via leaching and as gaseous emissions. These losses can be environmentally damaging and expensive in terms of lost agricultural production. Plants have evolved many traits to optimize nutrient acquisition, including the formation of arbuscular mycorrhizas (AM), associations of plant roots with fungi that acquire soil nutrients. There is emerging evidence that AM have the ability to reduce nutrient loss from soils by enlarging the nutrient interception zone and preventing nutrient loss after rain-induced leaching events. Until recently, this important ecosystem service of AM had been largely overlooked. Here we review the role of AM in reducing nutrient loss and conclude that this role cannot be ignored if we are to increase global food production in an environmentally sustainable manner.

Symbioses between plants and beneficial soil microorganisms like arbuscular-mycorrhizal fungi (AMF) are known to promote plant growth and help plants to cope with biotic and abiotic stresses. Profound physiological changes take place in the host plant upon root colonization by AMF affecting the interactions with a wide range of organisms below- and above-ground. Protective effects of the symbiosis against pathogens, pests, and parasitic plants have been described for many plant species, including agriculturally important crop varieties. Besides mechanisms such as improved plant nutrition and competition, experimental evidence supports a major role of plant defenses in the observed protection. During mycorrhiza establishment, modulation of plant defense responses occurs thus achieving a functional symbiosis. As a consequence of this modulation, a mild, but effective activation of the plant immune responses seems to occur, not only locally but also systemically. This activation leads to a primed state of the plant that allows a more efficient activation of defense mechanisms in response to attack by potential enemies. Here, we give an overview of the impact on interactions between mycorrhizal plants and pathogens, herbivores, and parasitic plants, and we summarize the current knowledge of the underlying mechanisms. We focus on the priming of jasmonate-regulated plant defense mechanisms that play a central role in the induction of resistance by arbuscular mycorrhizas.

Most plants grow in association with arbuscular mycorrhizal (AM) fungi in their roots forming the so-called AM symbiosis. AM symbiosis is usually beneficial to the host as it improves plant survival and performance. However, AM symbiosis also entails a cost to the plant in terms of the carbon allocated to the fungus. In sexually dimorphic plants, more than one type of individual can be recognised with regard to their sexual expression or gender. The cost of reproduction in these plants will differ in relation to the relative investment in male versus female function, as the female and the male sexual functions incur different costs. This different cost of reproduction may be translated into differences in other plant functions between the sexes as all functions are connected through trade-offs. Therefore, since sexes differ in resource needs and allocation patterns, and AM mediate resource acquisition and allocation patterns through imposing both costs and benefits to the plant, the sexes of dimorphic plant species may possess, at least theoretically, a different relationship with their AM roots symbionts. In this thesis, I have investigated whether the sexes in sexually dimorphic plant species differ in their mycorrhizal relationship, and if so, in which ways. Several plant life history traits were studied in the dioecious species Antennaria dioica and also in the gynodioecious Geranium sylvaticum using greenhouse, common-garden and field experiments. Resource acquisition, resource allocation, and both plant and fungal benefits from AM symbiosis were considered. Mainly beneficial effects of AM symbiosis were observed in both sexes of the two dimorphic plant species for most of the studied plant life history traits. Overall, both partners benefited from the AM association. However, several sex-specific benefits were detected which were not uniformly present in all experiments for any given trait. Moreover, the responses observed in certain life history trai

A time-course pot experiment was designed to compare the effect of two Rhizobium meliloti strains, the wild type (WT) and its genetically modified (GM) derivate, on the physiological activity of the arbuscular mycorrhizal (AM) fungus Glomus mosseae during the colonization of alfalfa (Medicago sativa L.) roots as affected by the water status in the growing medium using histochemical staining methods as succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) enzyme markers. At each harvest time, and for each water level, there were no significant differences in plant growth response between the effect of the two rhizobial WT and GM treatments on AM-plants. This is an unexpected result because the GM strain usually behaves as an improved rhizobial inoculant. Nodulation followed already described patterns, i.e. the GM strain produced less, but bigger, nodules than the WT strain. In spite of the lack of an improved growth response to the GM strain, this did not adversely affect the development of the AM symbiosis (Glomus mosseaeMedicago sativa). It was also found that, under well-watered conditions, about 80% of the AM mycelium in plants inoculated with the GM Rhizobium was alive (SDH activity) throughout the experiment, while only 10-20% of the intraradical mycelium remained alive in plants inoculated with the WT strain. Both rhizobial strains behaved similarly under water-limiting conditions in regard to AM development.