Impact of climatic factors on the propagation of Covid-19

Microbes are not always enemies of health…!!!

Our environment is teeming with an impressive diversity of microscopic organisms, including fungi, viruses, bacteria and single-celled protozoa. These tiny living beings, whether beneficial or harmful, have the capacity to regularly enter our body, whether through the air we breathe, the foods we consume or direct contact with contaminated surfaces.

Examples of infections by microorganisms

Influenza: Influenza is triggered by various viruses, including influenza A, B and C. The symptoms of this infectious disease are well known: fever, body aches, intense fatigue and often inflammation of the respiratory tract, manifested by a cough, sore throat and difficulty breathing. These symptoms can vary in intensity depending on the viral strain involved and the general health of the infected person.

Tuberculosis: Tuberculosis is an infectious disease caused by Koch's bacillus, scientific name Mycobacterium tuberculosis. It can affect various organs, but the most common form is pulmonary tuberculosis. Symptoms of this pulmonary form include a persistent, dry cough, prolonged fever, significant fatigue, and chest pain. At an advanced stage, nodules form in the lung tissues, which can develop into cavities. These cavities are characteristic of advanced tuberculosis and are often visible on chest x-rays.

Tetanus: Tetanus is an infection caused by the bacteria Clostridium tetani, which secretes a powerful toxin called tetanus toxin. This toxin acts on the central nervous system, causing characteristic symptoms. Initially, the disease manifests itself as painful muscle contractions, particularly in the neck, jaw and back. These muscle contractions can be so severe that they can lead to bone fractures.

Poliomyelitis: Poliomyelitis is a viral disease caused by the polio virus, also called poliovirus. This infection can manifest itself in different ways, but one of its most characteristic symptoms is paralysis, which can be partial or total depending on the severity of the nerve damage.

Mycoses: Mycoses are fungal infections caused by parasitic fungi. These fungi can infect different parts of the body, including the skin, mucous membranes, nails and even internal organs in some cases. Symptoms of skin fungal infections usually include skin lesions such as redness, itching, patches, blisters or cracks.

Malaria: Malaria, also known as malaria, is an infectious disease caused by a protozoan of the genus Plasmodium. The most common symptoms include episodes of intermittent fever, chills, headache, muscle pain, fatigue, and sometimes nausea and vomiting.

Routes of transmission of infections

There are several routes by which infections can be transmitted from one individual to another or from one environment to one individual. These transmission routes are essential to understand to prevent the spread of disease and take appropriate steps to reduce risk.

Airway

• Virus de la grippe
• Virus de la rubéole
• Bacille de la tuberculose

Digestive tract

• Salmonella
• Stomach flu virus
• Cholera bacillus

Dermal

• Tetanus bacillus
• Malaria parasite

Genital tract

• Syphilis bacteria
• AIDS virus
• Hepatitis B virus

Microorganisms play a useful role in food and industry

Microorganisms, such as bacteria, yeasts, molds and microscopic algae, have a significant impact in several aspects of food and industry. Their effective use can bring notable benefits in terms of food production, industrial processing and even sustainable development.

Food fermentation: Microorganisms are widely used in food fermentation to produce a diverse range of products. For example, lactic acid bacteria are used to ferment milk and produce yogurt, cheese, and other dairy products. Yeasts are essential in the production of bread, beer, wine and many other fermented products. These fermentation processes often impart unique flavors, pleasant texture and better preservation to foods.

Enzyme Production: Microorganisms are also used to produce enzymes used in various industrial processes. Microbial enzymes are used in the food industry for the production of sugar, the refining of oils, the production of fruit juices and the processing of certain foods to improve their texture and taste.

Food biotechnology: Advances in biotechnology have made it possible to use genetically modified microorganisms to produce nutritionally enhanced foods, such as cultures of bacteria that produce essential vitamins or amino acids. This approach can help combat nutritional deficiencies in certain populations.

Waste Degradation: Some microorganisms are capable of degrading organic and industrial waste, which is crucial for wastewater treatment, decomposition of agricultural waste and ecological waste management in industry.

Production of antibiotics and drugs: Microorganisms are an important source of antibiotics and medicinal substances. Many antibiotics used in medicine are produced by microorganisms such as fungi and bacteria. Additionally, research on microorganisms is used to develop new drugs and treatments in the pharmaceutical field.

What are the main origins of microorganisms in the natural environment?

Microorganisms in the natural environment come from a variety of sources, and their presence is essential for ecological balance and the functioning of ecosystems. Here are some of the main origins of microorganisms in the environment:

Soil: Soil is one of the main sources of microorganisms in the environment. It is home to an incredible diversity of bacteria, fungi, protozoa and other organisms. These microorganisms play a crucial role in breaking down organic matter, cycling nutrients, and forming soil structure.

Water: Aquatic environments, such as lakes, rivers, oceans and groundwater, are rich in microorganisms. Bacteria, algae, protozoa and viruses are found in these aquatic environments, where they participate in biogeochemical processes, primary production and the regulation of water quality.

Air: Although air is less dense in microorganisms than soil and water, it still contains bacteria, fungal spores, and viruses carried by air currents. These microorganisms may play a role in the dispersal of diseases, the formation of clouds and aerosols, as well as in certain atmospheric biogeochemical processes.

Plants and animals: The surfaces of plants and animals are also habitats for many microorganisms. The leaves, roots and stems of plants are home to beneficial bacteria and fungi, such as rhizobia and mycorrhizae, which contribute to plant nutrition. Animals, including humans, also have complex microbiomes on their skin, in their digestive tract, and on other body surfaces.

Natural deposits and reservoirs: Certain specific environments, such as swamps, peatlands, hot springs, saline soils, and natural deposits of organic matter, are important reservoirs of microorganisms adapted to particular environmental conditions. These unique habitats may support rare or extremophile species with unique adaptations.

Human activities: Finally, human activities can also introduce microorganisms into the environment, whether intentionally (e.g., seeding soils with beneficial microorganisms) or unintentionally (e.g., bacterial pollution from human waste ).

Soil Microbiology

Soils support a wide variety of microorganisms, including eukaryotes such as fungi, algae and protozoa, as well as prokaryotes such as bacteria and cyanobacteria. Their diversity is notable and their distribution depends on various environmental factors, such as the presence of organic matter (notably plant residues) and mineral elements, as well as the specific physicochemical conditions of each soil, such as its structure, its aeration. , its pH, its temperature and its humidity level.

Soil microbiology focuses on the study of the microorganisms that constitute the soil microbiota, also called soil microbiota. This microbiota includes eukaryotic and prokaryotic microorganisms, as well as viruses, forming the second trophic level by feeding on plants and their debris, which constitute the first trophic level. Soil microbiology scientifically examines the microscopic population present in the soil.

Presentation of soil microbiology

Objectives of soil microbiology

Soil microbiology is a part of microbial ecology and primarily focuses on analyzing the role of microorganisms within the sub-ecosystem called the soil-plant system, which includes soil, microflora, soil fauna and plants.

Soil biodiversity

Soil is not limited to being a simple support for plants, providing them with the nutrients necessary for their growth. It also constitutes a remarkable reservoir of microorganisms, notably fungi and bacteria, characterized by its diversity and density. Soil plays a crucial role in preserving biodiversity, both on the surface and at depth. Underground diversity is considerable, but often underestimated. In fact, one gram of soil with vegetation contains around a billion bacteria divided into 5,000 to 25,000 species, most of which remain unknown and cannot be cultivated in the laboratory.

                                     

Actinomycetes, present in large numbers in soils, join other bacteria and fungi to act as environmental cleaners and contribute to the formation of humus.

The presence of microorganisms in the soil depends on its depth; Indeed, the bacterial population decreases with depth, probably due to the reduction in the supply of organic matter and oxygen. Actinomycetes, which are filamentous bacteria, show a similar tendency and contribute to the decomposition of organic matter. The fungi, although few in number, remain relatively constant and their population decreases slightly at depth, probably due to the reduced availability of organic substrates. Algae, on the other hand, are mainly found in the surface layers of the soil, which makes sense given their need for light for photosynthesis.

Microorganisms in soil can be classified in different ways:

• According to their characteristics such as morphology, metabolism and nutrient sources;
• Based on their genome;
• According to the broad categories of functions they perform.

Alongside fungi, soil bacteria are considered the chemical architects of soil. They perform a wide range of functions, including decomposition of organic matter, nitrogen cycling, phosphorus availability and pesticide degradation. Additionally, they can help regulate root growth.

The main functional categories of microorganisms present in soils

Examples of functional categories that participate in the nitrogen cycle

• Nitrogen-fixing bacteria: They convert atmospheric nitrogen (N2) into compounds that can be assimilated by plants, such as ammonia. These bacteria include symbionts that reside in the rhizosphere of cultivated plants, such as Rhizobium in legumes.
• Ammonifying bacteria: They break down organic matter rich in nitrogen into ammonia or ammonium ions.
• Nitrifying bacteria: They promote the oxidation of ammonia into nitrate.

Examples of functional groups involved in the degradation of organic materials

• Cellulolytic bacteria: They specialize in breaking down cellulose, the most abundant structural molecule in plants. This group plays an essential role in the dynamics of organic matter.
• Pectinolytic bacteria: They are responsible for the degradation of pectin and its derivatives. Among these, the most commonly present bacteria often belong to the genus Arthrobacter.

Preservation of the structural state of the soil

Preserving soil structure is essential, and microbial communities, particularly bacteria, play an important role in this process. These bacteria produce mucilages rich in carbohydrates and proteins, which stabilize soil microaggregates thanks to their adhesive properties. Furthermore, the development of fungal hyphae contributes to the stabilization of macroaggregates. This synergy gives the soil a granular structure, improves its water retention capacity and increases its resistance to erosion.

Soil aggregates, also called "elementary assemblages", are made up of the combination of mineral particles, various cements (organic, oxides, hydroxides, etc.) and internal voids. Their size, generally of the order of a millimeter, makes them visible to the naked eye.

Soil microorganisms play two essential roles: on the one hand, they participate in numerous chemical and sometimes physical transformations within the soil; on the other hand, they directly or indirectly influence plant nutrition. Indeed, there is a network of complex interactions between soil microorganisms, plants, soil fauna, as well as the chemical and physical elements that constitute the soil-plant system.

Function of microorganisms present in the soil

The soil microbiota plays a crucial and varied role, including humification and mineralization, mycorrhization, atmospheric nitrogen fixation, as well as plant protection by endophytic fungi. A mycorrhiza is the result of a symbiotic association, called mycorrhization, which forms between fungi and plant roots.

Mycorrhizae work with soil bacteria to break down minerals and make phosphorus available to plants. This ability to regulate the transfer of phosphorus from the soil to the plant constitutes the main function of the mycorrhiza in symbiotic interactions.

Humus refers to the upper layer of soil formed by the decomposition of organic matter, mainly through the joint activity of soil animals, bacteria and fungi. It comes from the degradation of fresh organic matter such as plant debris, animal carcasses and excrement, under the action of micro-organisms such as bacteria, fungi and soil microfauna, including earthworms. , insects, small arthropods, nematodes, etc.

A clay-humic complex consists of negatively charged colloids of organic and inorganic matter, as well as positively charged mineral ions. These elements bind humus and clay together, forming the aggregates that make up soil. This complex has a strong adsorption capacity, which allows it to retain numerous minerals, thus creating a bond between clay, mineral elements and humus.

Exudates are complex organic substances, often liquid, emanating from certain plant species, mainly trees, when affected by diseases or injuries, or emanating more generally from roots. Their goal is to heal wounds and prevent infections caused by bacteria and insects.

Litter refers to all the decomposing organic debris found on the surface of the soil.

Beneficial effects of soil microorganisms

Soil microbial communities, essential in the biogeochemical cycles of carbon, nitrogen and other elements, also have positive or negative impacts on plant growth and health.

Pathogenic microorganisms are uncommon. On the other hand, many of them stimulate plant growth, help break down pollutants and produce beneficial compounds such as enzymes, antibiotics or other molecules like antivirals and anti-tumor agents.

Among the beneficial microorganisms are mycorrhizal fungi, which form close associations with plants. They provide them with essential nutrients, notably phosphorus, which promotes their growth and strengthens their natural defenses against biotic and abiotic stress.

Other microorganisms, such as bacteria of the genera Bacillus or Pseudomonas, can also stimulate plant growth and neutralize the activity of pathogens. Soil bacteria break down organic molecules by secreting enzymes into their environment, facilitating their hydrolysis into simple molecules that can be absorbed through their cell wall and plasma membrane.

Soil microorganisms function as a reservoir of mineral elements, retaining these elements in the upper layers of the soil to protect them against leaching, thus making them more accessible to plants:

• They play an essential role in the decomposition and mineralization of decomposing organic matter;
• They facilitate the release of essential nutrients for plants;
• They help maintain a solid soil structure and promote the formation of humus.

Soil microbiology is a fundamental element of soil biology. Microorganisms play a crucial role in soil health, in particular by promoting their biological fertility, whether in terrestrial or aquatic environments.

In addition to their contribution to fertility, soil microorganisms are essential for nutrient cycles, essential to maintaining life on Earth. Unfortunately, past agricultural practices have not always promoted healthy populations of microorganisms, limiting agricultural yields and compromising the sustainability of systems.

Role of mushrooms

Typically, fungi make up more than half of the soil microbial biomass. However, in hydromorphic soils, algae tend to proliferate on the surface, while anaerobic bacteria develop deeper. Viruses, often associated with clay particles, can enter plant roots through lesions. Soil also contains free enzymes, which can be intracellular (present inside living or dead cells) or extracellular (free or adsorbed on clay colloids). In addition to microflora, the soil supports microfauna, including nematodes, earthworms and other invertebrates, including insects, which also play a significant role.

Role of microfauna

Microfauna includes tiny animals, measuring less than 0.2 mm, found in specific environments. Although discreet, it plays an essential role in the formation and evolution of soils and sediments, as well as in the decomposition of dead wood and animal corpses.

The soil microbiota plays a crucial and varied role, including humification, mineralization, mycorrhization, atmospheric nitrogen fixation, and plant defense by endophytic fungi.

Where are the microfauna found?

Microfauna, present in the soil and particularly in humus, includes animals and other organisms that are often very small. It plays an essential role in the decomposition of organic matter.

Role of bacteria

Soils contain an abundance of bacteria, with an average of one billion individuals per gram of soil (equivalent to approximately 2.5 tonnes of carbon per hectare). These prokaryotic organisms, among the smallest in the soil, measure between 1 and 2 micrometers in length and can live in aerobic (presence of oxygen) or anaerobic (absence of oxygen) conditions.

Within the legume family, which includes three subfamilies (Papilionaceae, Mimosaceae and Cesalpiniaceae), the ability to form nodules and therefore to fix nitrogen is not universal. This ability is very common in Papilionaceae and Mimosaceae, but much less common in Caesalpiniaceae. Furthermore, among species capable of fixing nitrogen, there is great variability, both between different species and within the same species, regarding their ability to fix nitrogen.

By the mid-1990s, more than two hundred actinorhizal species, mainly woody species, were known and distributed in eight families. The processes of nodulation and nitrogen fixation are similar, although slightly different, to those observed in legumes. The nodules of these plants are often durable and can reach considerable dimensions, up to 50 cm in diameter in certain species such as Allocasuarina verticillata. The nitrogen fixation potential can be as high as that of legumes, reaching up to 40 g of fixed nitrogen per tree per year in the first few years, or around 120 kg per hectare per year for one plantation of 3,000 trees per hectare.

It is important to note that the maximum nitrogen fixation capacity of any symbiosis is only achieved when limiting factors are absent. This fundamental ecological rule is sometimes overlooked because it can be difficult to identify the factors that limit symbiotic activity in a given environment.

Bacteria take up nitrogen and release it in a form that plants can assimilate. Indeed, once captured by bacteria, nitrogen in a non-assimilable form is transformed to become available in the soil in a form assimilable by crops, mainly in the form of nitrates (NO3-) or ammonium (NH4+). . These are the only forms of nitrogen that plants can absorb through their roots. There are four categories of bacteria capable of fixing atmospheric nitrogen and carrying out these transformations.

Symbiotic fixatives, belonging to the rhizobia family of microorganisms, form a symbiotic association with leguminous plants, living in symbiosis with them. Nitrogen fixation occurs at nodules, structures formed on plant roots. For example, Bradyrhizobium japonicum is a rhizobium species commonly associated with soybean crops.

Inside the nodules, symbiotic exchanges occur between the roots of the plant and the bacteria: the symbiotic fixatives feed on the carbon compounds released by the roots, while in return, they fix atmospheric nitrogen and transform it into a form assimilated by the roots.

In ecology and the field of Earth sciences, a biogeochemical cycle designates the cyclical journey of an element or a chemical compound through the main reservoirs which are the geosphere, the atmosphere and the hydrosphere, with implications in the biosphere.

A biogeochemical cycle describes the processes by which an element moves from one environment to another before returning to its starting point, thus forming a continuous recycling loop.

The carbon cycle refers to the movement of carbon in its different forms between the earth's surface, its interior and the atmosphere. Key mechanisms of this exchange include photosynthesis, respiration and oxidation.

The nitrogen cycle is a biogeochemical process which describes the successive transformations of different forms of nitrogen (dinitrogen, nitrate, nitrite, ammonia, and organic nitrogen such as proteins). The atmosphere, containing mainly dinitrogen at a concentration of 78% by volume, constitutes the main source of nitrogen.

Microorganisms play a crucial role in the biogeochemical cycles of the biosphere, significantly influencing the metabolism of carbon (C) and sulfur (S), the flux of nitrogen (N) and the mobilization of phosphorus (P) in the 'environment. Organic matter (OM) must undergo mineralization to be assimilated by plants. By breaking down OM for their own resource needs, microorganisms promote the release of mineral elements into the soil, making them accessible to plants. Additionally, many microorganisms present in the rhizosphere directly contribute to plant growth by acting as plant growth-promoting rhizobacteria (PGPR).

The main stages of mineralization are as follows:

• Ammonification, which converts the amino nitrogen of proteins into ammonia (NH4).
• Nitrosation, which transforms ammonia into nitrites (NO2).
• Nitratation, which converts nitrites into nitrates (NO3).

The phosphorus cycle encompasses all biogeochemical interactions involving phosphorus on our planet. This mineral is essential because it is a fundamental component of DNA, teeth, bones and shells.

Soil micro-organism-plant interaction

Soil microorganisms, such as bacteria and microscopic fungi, constantly interact with plant roots. These interactions can have various effects: deleterious when pathogenic microorganisms cause diseases (parasitism), neutral (commensalism), or beneficial for the growth and health of plants (mutualism).

The soil microbiota plays a crucial role in maintaining soil health through a series of complex activities and interactions with plants. It contributes to the structuring of soils: bacteria produce organic molecules which facilitate the formation of aggregates, thus improving soil aeration and water circulation.

Two examples of symbiotic interactions (with reciprocal beneficial effects) are:

1. Arbuscular mycorrhizal fungi, widely distributed, associate with plants to allow them to better exploit the water and mineral resources of the soil.
2. Nitrogen-fixing bacteria of the Rhizobium genus, which associate with plant roots, allow the fixation of atmospheric nitrogen to form nitrogen compounds. This symbiosis is mainly observed in a limited number of species, notably legumes.

Consideration of fungi in crop management

With their exceptional ability to connect to plant roots, microscopic fungal filaments greatly extend the root system. They draw water and nutrients from a large volume of surrounding soil and deliver them to the plant, improving its nutrition and growth.

The fungus secretes growth regulators, similar to plant hormones, which stimulate the development of the root system. This root system thus becomes denser and more branched, promoting better growth of the plant.

 Mycorrhizal Fungi

During mycorrhizal symbiosis, the fungus forms a close interaction with the plant by growing both inside the roots of the host plant and in the soil. The mycelium, which forms outside the roots, constitutes the first interface between the plant and the soil.

Mycorrhizal fungi establish symbiotic associations with the roots of 80 to 90% of plant species. In this mutually beneficial relationship, the fungus receives sugars and vitamins from the plant necessary for its growth. In return, it absorbs various elements from the soil, including phosphorus, which it transfers to the plant, thus considerably increasing the volume of soil explored by plants for their growth.

In agriculture, the use of mycorrhizal fungi could prevent many problems of organic soil degradation. The addition of pesticides, particularly fungicides, can have adverse effects on soil quality. Mushrooms play a crucial role in maintaining soil fertility. The addition of high phosphorus chemicals can deplete endomycorrhizal fungi in quantity and quality, thereby reducing the nutrient supply to crop plants.

 Endophytic fungi

Root endophytic fungi are distinguished by their ability to colonize the internal structures of a plant asymptomatically. Unlike mycorrhizal fungi, which grow in the rhizosphere while colonizing plants, endophytic fungi remain exclusively in the root tissues of their host. They assimilate nutrients from the host without causing symptoms of disease. Like mycorrhizal fungi, endophytic fungi contribute to growth and strengthen the host plant's resistance to abiotic stress.

 Saprophytic fungi

Saprophytic fungi feed on decaying organic matter, which has already been broken down or broken down by other organisms.

 Pathogenic/parasitic fungi

Pathogenic fungi can parasitize other fungi, animals or plants (like plant pathogens). Soil-borne plant pathogenic fungi have the ability to infect roots, penetrate vascular systems, and colonize the entire organism using xylem vessels, although their primary target is often the aerial parts of plants.

Influence of plants on microorganisms

• Significant proportion of soil microflora consists of heterotrophic organisms that rely on organic compounds for their source of energy and carbon.
• Essentially, these organic compounds are brought into the soil by plants.
• The soil rhizosphere is characterized by a notably higher concentration of organic compounds, which serve as substrates for microflora organisms.
• Organic compounds come not only from various root residues, but also from root exudation.
• A wide variety of substances are exuded, including carbohydrates such as polymers of pectic substances, largely present in the root cap, as well as amino acids, vitamins, organic acids and enzymes.

Vegetation exerts a crucial influence on the composition of soil microflora through various processes, including:

• Exudation of roots and seeds.
• The decomposition of residues of aerial organs (leaves, flowers, wood), known as litter.
• Mineral and organic substances are introduced via rainwater, formed when rainwater passes through the foliage as well as the bark of branches and trunks.

Plant symbioses - micro-organisms

Certain microorganisms capable of fixing nitrogen establish a symbiosis with various green plants. Three main groups are distinguished: Rhizobium, which form associations with legumes; Frankia, actinomycetes associated with actinorhizal plants (forming nodules); and cyanobacteria such as Nostoc and Anabaena, which are found in association with higher plants such as cycads or small aquatic ferns like Azolla.

In these systems, nitrogen fixation is carried out by a complex enzymatic assembly called nitrogenase. This complex converts atmospheric nitrogen (in molecular form) into ammonia, a combined form of nitrogen which is then assimilated by the host plant via specific metabolic pathways.

 Interest in the interaction

Nitrogen-fixing symbioses provide a crucial advantage by allowing legumes and actinorhizal plants to grow normally even in nitrogen-poor soils, without requiring the use of expensive and potentially polluting nitrogen fertilizers. When nitrogen fixation is effective, these plants can significantly enrich soils with nitrogen, helping to restore their fertility.

 Mechanism of interaction

The first phase of establishing the symbiosis between a legume and a nitrogen-fixing bacteria, such as Rhizobium, begins with infection of the plant's root. This process is based on a molecular exchange where the plant releases flavonoids and isoflavonoids which activate the nodule genes (nod genes) of the bacteria. This triggers the production and release of substances that promote infection of the plant and the formation of specialized nodules, called nodules or nodules. Rhizobium penetrate the root by various routes depending on the plant species, either through root hairs or by infiltrating between cortical cells. Inside the forming nodule, they multiply and, in most cases, penetrate the cytoplasm of the nodule cells. It is at this stage, once inside the nodule, that the Rhizobium begin to fix nitrogen. Nodules mainly form on the roots but can also appear on the stems of some legumes, known as stem or aerial nodules. In woody legumes, nodules can be persistent and reach up to 10 centimeters in diameter.

 Interaction between soil microorganisms and microfauna

Microfauna, invisible to the naked eye, is made up of organisms generally smaller than 200 micrometers, which allows them to live in capillary spaces in the soil. Although rotifers and tardigrades are part of this microfauna, it is mainly protozoa and nematodes that make up the majority. Protozoa, for example, can be abundant, with populations varying from 100 to 1000 million individuals per square meter.

This group has great nutritional diversity, but most protozoa feed by ingesting particles, mainly bacteria. They are classified into five trophic groups: bacterivores which consume bacteria, fungivores which feed on fungi, omnivores which consume both bacteria and fungi, phytoparasites which parasitize plants, and predators which feed on other animals.

Nematodes play a crucial role in the mineralization and decomposition of organic matter, as well as in the regulation of microbial communities.

Impact of pesticides on soil microorganisms

The widespread use of pesticides raises significant environmental and health concerns due to contamination of natural resources. Indeed, during their application, only part of the pesticides applied reaches their initial target, while the rest (30 to 50%) is found on the soil surface. These substances then disperse through various abiotic processes such as volatilization, wind erosion, leaching and runoff.

Effects of pesticides on microflora

When pesticides are applied to a crop, they do not reach their target 100%. Some of these products therefore end up reaching the soil, which can weaken various living organisms such as bacteria, fungi, earthworms and insects. This microflora is essential to soil fertility and must be preserved. In the long term, excessive use of pesticides can have harmful effects on the yield of an agricultural plot.

Pesticides pose a threat to soil microorganisms, which play a crucial role in essential processes such as carbon and nutrient cycling. Since soil life provides many ecosystem services, the adverse effects of pesticides could compromise soil health and, by extension, affect agricultural production.

Effects of pesticides on mycorrhizal fungi

The impact of pesticides on mycorrhizal fungi is particularly important because these organisms establish symbiotic associations with most land plants, including many crops. They play a crucial role in providing essential nutrients, sometimes up to 80% of plants' phosphorus needs, as well as other beneficial services such as improving soil structure and aggregation, and reducing nutrient losses through leaching and denitrification.

Functions of microflora in pesticide degradation

• Provided by bacteria and fungi
• Only part of the total microflora is made up of microbial biomass involved in degradation.
• Specific metabolism or cometabolism
• Total degradation
• It is possible that metabolites, i.e. transformation products, are produced.

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