Preface

Microorganisms such as mycorrhizal fungi are of utmost importance because they contribute directly to plant growth and soil health. Mycorrhizae means a symbiotic, mutualistic association between specialized fungi living in the soil and plant roots. We say that it is a symbiotic association since the plants benefit from increased nutrient and water acquisition and at the same time they provide photo-assimilates to the fungi. Most of the known species are symbiotic with mycorrhizal fungi such as dicotyledonous, monocotyledonous, and magnoliids. In addition to all the benefits for plants, mycorrhizae in the soil play several important roles for the ecosystem, such as food source for other animals, cycling and conservation of nutrients through the fungal mycelium, and improvement of soil structure.

Ectomycorrhizae are formed mainly by basidiomycetes and ascomycetes fungi. The mycorrhizae belong to the phylum glomeromycota; they reproduce asexually and form glomerospores as reproductive structures. The mycorrhizae form the mantle and the Hartig net, which is a net of hyphae that extends into the root of the plant, penetrating between the epidermal and cortical cells.

There are several plant growth-promoting mechanisms linked to mycorrhizae. Their direct benefits include improved soil quality and health, better sustainability of ecosystems and efficiency in the use of natural resources, good plant development, and increased tolerance to biotic and abiotic stresses. Regarding nutritional effects in plants, mycorrhizae allow for increased water and nutrient uptake, fine root longevity, and higher mineralization and solubilization of nutrients from minerals. Indirect benefits include greater nutrient turnover and cycling leading to an accumulation of these elements in the plant and roots. Also, there are no nutritional effects such as increased tolerance to heavy metals and pathogens and enhancement of soil quality.

Fungi produce glomalin, which is a protein secreted by the hyphae of arbuscular mycorrhizal fungi; it works like a "super glue," binding soil particles together into aggregates. This protein helps fix soil particles, allowing the formation of stable aggregates. In addition, glomalin sequesters heavy metals, reducing the availability and risk of toxicity of these elements for organisms and plants growing in polluted soils.

*Arbuscular Mycorrhizal Fungi in Agriculture - New Insights* provides a comprehensive overview of the mechanisms and benefits of mycorrhizae in three sections : "The Role of Mycorrhizae Fungi in Plant Growth", "The Effect of Mycorrhizae on Plant Nutrition and Protection", and "Mycorrhizae Biology and Development".
