Section B
Q - Discuss cross inoculant groups with examples.
A - Cross inoculant groups refer to the concept of using multiple microbial inoculants simultaneously or sequentially to enhance plant growth, health, and productivity. These inoculants can include beneficial bacteria, fungi, and other microorganisms that form synergistic relationships with plants.
Example -
Mycorrhizae-Plant Symbiosis
Plant Growth-Promoting Rhizobacteria (PGPR) - Bascillus . Pseudomonas.
Q - Write short note on Rhizobium .
A - Rhizobium is a genus of nitrogen-fixing bacteria that forms a symbiotic relationship with leguminous plants, contributing significantly to sustainable agriculture. Here's a short note on Rhizobium:
**Characteristics of Rhizobium:**
- **Nitrogen Fixation**: Rhizobium bacteria have the unique ability to fix atmospheric nitrogen into a form that plants can utilize. This process occurs within nodules formed on the roots of leguminous plants.
- **Symbiotic Relationship**: Rhizobium forms a mutualistic symbiosis with legumes such as soybeans, peas, beans, alfalfa, and clover. The bacteria provide nitrogen to the plant, while the plant supplies carbon and energy sources to the bacteria.
- **Root Nodule Formation**: Upon infection by Rhizobium, legume roots develop specialized structures called nodules. Inside these nodules, Rhizobium converts nitrogen gas (N2) into ammonia (NH3) through nitrogenase enzymes, making it available for plant growth.
- **Indeterminate Growth**: Rhizobium nodules exhibit indeterminate growth, meaning they continue to fix nitrogen as long as favorable conditions persist.
- **Species Diversity**: The genus Rhizobium comprises various species and strains, each adapted to specific legume host plants. Different species of Rhizobium can form nodules on different legume species.
**Role of Rhizobium in Agriculture:**
- **Nitrogen Fixation**: Rhizobium plays a crucial role in biological nitrogen fixation, reducing the need for synthetic nitrogen fertilizers and promoting sustainable farming practices.
- **Improved Soil Fertility**: By converting atmospheric nitrogen into a plant-available form, Rhizobium contributes to soil fertility and nutrient cycling, benefiting both crops and subsequent plantings.
- **Enhanced Crop Yields**: Legumes inoculated with compatible Rhizobium strains typically exhibit improved growth, higher yields, and better nutrient utilization.
- **Environmental Benefits**: Reduced nitrogen runoff and leaching, as well as minimized greenhouse gas emissions (e.g., nitrous oxide), contribute to environmental sustainability.
Q - Write short note on Actinorhizal plants give example.
A - Actinorhizal plants are a group of woody plants that form a unique symbiotic relationship with nitrogen-fixing bacteria known as actinomycetes. This symbiosis occurs in specialized structures called root nodules, similar to the nodules formed in leguminous plants with rhizobia bacteria. Actinorhizal plants are important contributors to soil fertility and ecosystem health.
ex - bay berry, alder tree , sheoak , silverberry.
**Importance of Actinorhizal Plants:**
- **Soil Improvement**: Actinorhizal plants contribute to soil fertility and health by adding nitrogen through symbiotic nitrogen fixation, enhancing soil structure, and supporting microbial diversity.
- **Ecological Restoration**: Actinorhizal plants are used in ecological restoration projects to revegetate degraded lands, stabilize soils, and promote ecosystem resilience.
- **Agroforestry**: Actinorhizal plants, including alders, are utilized in agroforestry systems to provide nitrogen inputs, improve soil quality, and diversify crop production.
- **Carbon Sequestration**: Actinorhizal plants contribute to carbon sequestration by storing carbon in woody biomass and enhancing soil organic matter.
Q - Define algal Biofertilizers.
A - Algal biofertilizers, also known as algal inoculants or algal biofertilization agents, are products derived from various species of algae (microalgae or macroalgae) that are used to enhance soil fertility and promote plant growth. These biofertilizers harness the natural abilities of algae to fix atmospheric nitrogen, solubilize phosphorus, produce plant growth-promoting substances, and improve soil structure.
Q - Write short note on Biofertlizers.
A - Biofertilizers are natural substances containing living microorganisms that promote plant growth by enhancing nutrient availability, improving soil structure, and suppressing soil-borne pathogens. These biological agents play a crucial role in sustainable agriculture by reducing the reliance on chemical fertilizers and supporting environmentally friendly farming practices. 2
**Characteristics of Biofertilizers:**
1. **Microbial Content**: Biofertilizers primarily contain beneficial microorganisms such as nitrogen-fixing bacteria, phosphate-solubilizing bacteria, mycorrhizal fungi, and plant growth-promoting rhizobacteria (PGPR).
2. **Nutrient Enhancement**: They enhance nutrient availability in the soil by fixing atmospheric nitrogen, solubilizing phosphorus, mobilizing potassium, and synthesizing growth-promoting substances like vitamins, amino acids, and enzymes.
3. **Soil Improvement**: Biofertilizers improve soil fertility, structure, water-holding capacity, and microbial activity, leading to healthier soils and increased nutrient uptake by plants.
4. **Environmentally Friendly**: They reduce chemical fertilizer usage, minimize nutrient runoff and leaching, mitigate soil degradation, and contribute to sustainable agriculture practices.
5. **Biostimulant Effects**: Biofertilizers act as biostimulants, promoting root development, nutrient absorption, seed germination, flowering, fruiting, and stress tolerance in plants.
6. **Compatibility**: Biofertilizers are compatible with organic farming methods and can be used in conjunction with other organic inputs like compost, manure, and biopesticides.
**Types of Biofertilizers:**
1. **Nitrogen Fixing Biofertilizers**: Contain nitrogen-fixing bacteria (e.g., Rhizobium, Azotobacter, Azospirillum) that convert atmospheric nitrogen into plant-available forms.
2. **Phosphate Solubilizing Biofertilizers**: Include phosphate-solubilizing bacteria (e.g., Bacillus, Pseudomonas) and mycorrhizal fungi that release bound phosphorus for plant uptake.
3. **Potassium Mobilizing Biofertilizers**: Utilize potassium-mobilizing bacteria (e.g., Bacillus mucilaginosus) to enhance potassium availability to plants.
4. **Organic Matter Decomposers**: Comprise beneficial microbes that decompose organic matter, releasing nutrients and improving soil health.
5. **Plant Growth-Promoting Biofertilizers**: Contain PGPR (e.g., Azospirillum, Bacillus, Pseudomonas) that produce growth hormones, enzymes, and siderophores, promoting plant growth and health.
6. **Mycorrhizal Biofertilizers**: Include mycorrhizal fungi (e.g., Glomus, Rhizophagus) that form symbiotic relationships with plant roots, enhancing nutrient uptake and drought tolerance.
Q - Write about importance of NPK ?
A - NPK refers to the three primary nutrients essential for plant growth: nitrogen (N), phosphorus (P), and potassium (K). These nutrients play crucial roles in various physiological processes within plants, contributing significantly to their overall health, development, and productivity.
**1. Nitrogen (N):**
- **Role**: Nitrogen is a key component of proteins, enzymes, chlorophyll, and nucleic acids essential for plant growth and metabolism.
- **Importance**:
- **Leaf Growth**: Nitrogen promotes the development of healthy foliage, green leaves, and overall plant vigor.
- **Protein Synthesis**: Essential for the synthesis of amino acids and proteins, crucial for cell division, structure, and function.
- **Photosynthesis**: Chlorophyll, the pigment responsible for photosynthesis, contains nitrogen, facilitating energy production from sunlight.
- **Yield and Quality**: Adequate nitrogen availability is linked to increased crop yield, improved crop quality, and higher protein content in grains.
- **Stress Tolerance**: Nitrogen enhances plants' ability to withstand environmental stresses like drought, heat, and pest attacks.
**2. Phosphorus (P):**
- **Role**: Phosphorus is involved in energy transfer, root development, flowering, fruiting, and nutrient uptake processes.
- **Importance**:
- **Root Growth**: Phosphorus promotes strong root development, improving nutrient and water absorption efficiency.
- **Energy Transfer**: ATP (adenosine triphosphate), the energy currency of cells, requires phosphorus for synthesis, supporting various metabolic processes.
- **Blooming and Fruit Set**: Phosphorus aids in flower formation, pollination, fruit set, and seed development, influencing crop yield and quality.
- **Nutrient Transport**: Facilitates the movement of nutrients within plants, contributing to overall growth and functioning.
- **Disease Resistance**: Adequate phosphorus levels enhance plants' resistance to diseases and pathogens, promoting overall plant health.
**3. Potassium (K):**
- **Role**: Potassium regulates water uptake, osmotic balance, enzyme activation, and nutrient transport within plants.
- **Importance**:
- **Water Management**: Potassium regulates stomatal opening and closure, reducing water loss through transpiration and improving drought tolerance.
- **Osmotic Regulation**: Maintains cell turgor pressure, osmotic balance, and cell integrity, especially during periods of water stress.
- **Enzyme Activation**: Activates numerous enzymes involved in photosynthesis, respiration, and protein synthesis, supporting metabolic processes.
- **Nutrient Uptake**: Enhances the uptake of other essential nutrients, including nitrogen and phosphorus, promoting balanced plant nutrition.
- **Disease and Pest Resistance**: Potassium contributes to plant defense mechanisms, enhancing resistance against diseases, pests, and environmental stresses.
**Importance of Balanced NPK Ratios**:
- **Optimal Growth**: Balanced NPK ratios ensure that plants receive adequate nutrients for healthy growth, development, and reproduction.
- **Yield and Quality**: Proper NPK nutrition contributes to increased crop yields, improved crop quality (e.g., size, color, taste), and better nutritional value.
- **Crop Health**: Maintaining balanced NPK levels supports plant health, resilience to diseases, pests, and environmental stresses, reducing yield losses.
- **Soil Fertility**: NPK nutrients are vital for maintaining soil fertility, organic matter decomposition, nutrient cycling, and sustainable agricultural practices.
Section C
Q - Discuss bacteria associated to nitrogen fixation.
A - Bacteria associated with nitrogen fixation play a crucial role in the nitrogen cycle by converting atmospheric nitrogen (N2) into a plant-usable form, ammonia (NH3), or nitrate (NO3^-). This process, known as biological nitrogen fixation, is vital for maintaining soil fertility, supporting plant growth, and sustaining ecosystems. Here's a discussion of the key bacteria associated with nitrogen fixation:
### 1. **Rhizobium spp.:**
- **Symbiotic Relationship**: Rhizobium bacteria form symbiotic associations with leguminous plants such as soybeans, peas, clover, and alfalfa.
- **Nodule Formation**: Rhizobia infect plant roots, leading to the formation of specialized structures called root nodules where nitrogen fixation occurs.
- **Nitrogenase Enzyme**: Inside nodules, rhizobia produce the nitrogenase enzyme complex that catalyzes the conversion of atmospheric nitrogen to ammonia.
- **Leghemoglobin**: Rhizobia also produce leghemoglobin, which helps create an oxygen-limited environment within nodules, facilitating nitrogenase activity.
- **Benefits**: Rhizobium-plant symbiosis provides legumes with a direct source of nitrogen, reducing the need for synthetic fertilizers and improving soil fertility.
### 3. **Azotobacter spp.:**
- **Free-Living Nitrogen Fixers**: Azotobacter species are free-living bacteria found in soil, capable of atmospheric nitrogen fixation.
- **Aerobic Conditions**: Azotobacter thrives in aerobic conditions and contributes to soil nitrogen cycling and fertility.
- **Nitrogenase Enzyme**: These bacteria produce nitrogenase enzymes that fix atmospheric nitrogen into ammonia, which can be utilized by plants.
- **Biofertilizers**: Certain Azotobacter strains are used as biofertilizers to enhance soil fertility and support plant growth, especially in non-leguminous crops.
### 4. **Clostridium spp.:**
- **Anaerobic Nitrogen Fixers**: Some species of Clostridium, such as *Clostridium pasteurianum*, are anaerobic bacteria capable of nitrogen fixation.
- **Nitrogenase Activity**: Clostridium bacteria possess nitrogenase enzymes that convert atmospheric nitrogen into ammonia under anaerobic conditions.
- **Presence in Soils**: These bacteria contribute to nitrogen fixation in anaerobic environments, such as waterlogged soils and sediments.
### 5. **Frankia spp.:**
- **Actinomycete Bacteria**: Frankia species are filamentous, nitrogen-fixing bacteria belonging to the actinomycetes group.
- **Actinorhizal Symbiosis**: Frankia forms symbiotic associations with certain woody plants called actinorhizal plants, including alders, elms, casuarinas, and bayberry.
- **Root Nodule Formation**: Frankia induces the formation of root nodules in actinorhizal plants, where nitrogen fixation occurs.
- **Role in Ecosystems**: Frankia-actinorhizal symbiosis contributes to nitrogen cycling, soil fertility, and ecosystem restoration, especially in nitrogen-poor environments.
### Importance of Nitrogen-Fixing Bacteria:
- **Nutrient Cycling**: Nitrogen-fixing bacteria play a vital role in cycling nitrogen between the atmosphere, soil, and plants, ensuring a continuous supply of this essential nutrient.
- **Soil Fertility**: These bacteria enhance soil fertility by providing plants with nitrogen, promoting healthy growth, and reducing the need for synthetic fertilizers.
- **Sustainable Agriculture**: Harnessing the nitrogen-fixing capabilities of these bacteria supports sustainable agricultural practices, improves crop yields, and minimizes environmental impacts associated with nitrogen pollution.
- **Ecosystem Health**: Nitrogen-fixing bacteria contribute to ecosystem health, biodiversity, and resilience by supporting plant diversity, nutrient availability, and soil productivity.
Q - Discuss K solublization in details.
A - Potassium (K) solubilization refers to the process by which potassium, an essential nutrient for plant growth, is made available in soluble forms for uptake by plants. While potassium is abundant in soils, it often exists in forms that are not readily available for plant uptake, such as insoluble minerals or fixed within soil particles. K solubilization involves converting these unavailable forms into soluble potassium ions (K⁺) that plants can absorb through their roots. Here's a detailed discussion of K solubilization:
### 1. **Importance of Potassium (K) for Plants:**
- **Nutrient Uptake**: Potassium is one of the three primary nutrients (NPK) essential for plant growth, alongside nitrogen and phosphorus. It plays a vital role in various physiological processes.
- **Osmotic Regulation**: Potassium helps regulate osmotic balance in plant cells, maintaining cell turgor pressure and water uptake.
- **Enzyme Activation**: It activates many enzymes involved in photosynthesis, respiration, protein synthesis, and carbohydrate metabolism.
- **Stress Tolerance**: Potassium contributes to plant stress tolerance, enhancing resistance to drought, salinity, pests, and diseases.
- **Yield and Quality**: Adequate potassium levels are crucial for maximizing crop yields, improving crop quality, and enhancing nutritional value.
### 2. **Insoluble Forms of Potassium in Soils:**
- **Minerals**: Potassium is found in minerals such as feldspar, mica, and clay minerals, where it is tightly bound and insoluble.
- **Fixation**: Potassium ions can become fixed or immobilized within soil particles, reducing their availability for plant uptake.
- **pH Effects**: Soil pH influences potassium availability, with acidic soils often having higher soluble potassium and alkaline soils limiting potassium availability.
### 3. **K Solubilization Mechanisms:**
- **Microbial Activity**: Various soil microorganisms play a role in K solubilization through different mechanisms.
- **Acidification**: Some bacteria and fungi produce organic acids (e.g., gluconic acid, citric acid) that lower soil pH, releasing potassium from minerals.
- **Chelation**: Microorganisms produce chelating agents (e.g., siderophores) that bind to potassium ions, making them more soluble and available for plants.
- **Ion Exchange**: Microbial biomass and exudates can exchange ions with soil particles, releasing potassium into the soil solution.
- **Weathering Processes**: Natural weathering processes, including physical and chemical weathering, can gradually release potassium from rocks and minerals over time.
- **Root Exudates**: Some plants release compounds from their roots (root exudates) that can facilitate K solubilization by interacting with soil particles or microbial activity.
- **Organic Matter Decomposition**: Decomposition of organic matter in soils can release soluble potassium, contributing to K availability.
### 4. **Factors Affecting K Solubilization:**
- **Microbial Diversity**: Soil microbial communities vary in their ability to solubilize potassium, with certain species of bacteria, fungi, and actinomycetes being more effective.
- **pH Levels**: Soil pH influences K solubility, with slightly acidic to neutral pH ranges (pH 6.0-7.5) often favoring optimal K availability.
- **Moisture and Temperature**: Adequate soil moisture and temperature conditions support microbial activity and nutrient cycling, including K solubilization.
- **Organic Inputs**: Adding organic amendments (e.g., compost, manure) to soils can contribute to K solubilization over time as organic matter decomposes.
Q - Write classification , morphology and mode of action of azotobactor.
A - **Classification of Azotobacter:**
Azotobacter is a genus of nitrogen-fixing bacteria belonging to the family Pseudomonadaceae within the class Gammaproteobacteria. It comprises free-living, aerobic, and non-sporulating bacteria that play a significant role in nitrogen cycling and soil fertility.
**Morphology of Azotobacter:**
1. **Shape**: Azotobacter cells are typically rod-shaped (bacillus) or oval, occurring singly or in pairs.
2. **Size**: The size of Azotobacter cells ranges from 1.5 to 2.5 micrometers in width and 2 to 5 micrometers in length.
3. **Motility**: Most Azotobacter species are motile due to the presence of polar flagella, which aid in their movement in liquid environments.
4. **Cell Wall**: They possess a Gram-negative cell wall structure with an outer membrane, periplasmic space, and inner cytoplasmic membrane.
5. **Colonies**: Azotobacter colonies on agar media are often mucoid, smooth, and round, exhibiting various colors such as yellow, brown, or green.
**Mode of Action of Azotobacter:**
1. **Nitrogen Fixation**:
- **Enzymatic Activity**: Azotobacter species possess nitrogenase enzymes (mo-Fe protein and Fe protein) that catalyze the conversion of atmospheric nitrogen (N2) into ammonia (NH3), a plant-usable form of nitrogen.
- **Energy Requirement**: Nitrogen fixation is an energy-intensive process, requiring ATP generated through aerobic respiration to fuel nitrogenase activity.
- **Oxygen Sensitivity**: Azotobacter performs nitrogen fixation under aerobic conditions but is sensitive to high levels of oxygen, requiring mechanisms like leghemoglobin and respiratory protection to maintain nitrogenase activity.
2. **Secretion of Growth-Promoting Substances**:
- **Vitamins and Amino Acids**: Azotobacter species secrete vitamins (e.g., B group vitamins) and amino acids that promote plant growth and development.
- **Phytostimulants**: They produce growth-promoting substances like auxins, cytokinins, and gibberellins, enhancing root growth, nutrient uptake, and overall plant vigor.
3. **Phosphate Solubilization**:
- **Organic Acids**: Some Azotobacter strains produce organic acids (e.g., gluconic acid, citric acid) that solubilize phosphate compounds in the soil, making phosphorus more available to plants.
- **Chelation**: Azotobacter can chelate metal ions, including phosphorus, through the secretion of chelating agents, facilitating nutrient uptake by plants.
4. **Plant Growth Promotion**:
- **Nitrogen Supply**: By fixing atmospheric nitrogen and secreting nitrogenous compounds, Azotobacter enhances nitrogen availability in soils, supporting plant nutrition and growth.
- **Biocontrol Effects**: Some Azotobacter strains exhibit antagonistic activity against plant pathogens, contributing to disease suppression and plant health.
- **Soil Aggregation**: Azotobacter promotes soil aggregation and structure by producing extracellular polysaccharides (EPS), which improve soil water retention and aeration.
Q - Write classification , morphology and mode of action of azospirillum. +
A - **Classification of Azospirillum:**
Azospirillum is a genus of nitrogen-fixing bacteria classified within the family Rhodospirillaceae, order Rhodospirillales, and class Alphaproteobacteria. These bacteria are known for their ability to fix atmospheric nitrogen and promote plant growth, particularly in association with grasses and cereals.
**Morphology of Azospirillum:**
1. **Shape**: Azospirillum cells are spiral or helical-shaped, giving them a characteristic spirillum morphology.
2. **Size**: The size of Azospirillum cells ranges from 0.5 to 1.5 micrometers in width and 2 to 6 micrometers in length.
3. **Motility**: Most Azospirillum species are motile due to the presence of one or more polar flagella, which enable them to move in liquid environments.
4. **Cell Wall**: They possess a Gram-negative cell wall structure with an outer membrane, periplasmic space, and inner cytoplasmic membrane.
5. **Colonies**: Azospirillum colonies on agar media are typically smooth, mucoid, and slightly raised, with a translucent or whitish appearance.
**Mode of Action of Azospirillum:**
1. **Nitrogen Fixation**:
- **Association with Roots**: Azospirillum establishes a beneficial association with plant roots, especially grasses and cereals, where it colonizes the rhizosphere and root surface.
- **Nitrogenase Activity**: The bacteria possess nitrogenase enzymes (mo-Fe protein and Fe protein) that facilitate the conversion of atmospheric nitrogen (N2) into ammonia (NH3), which plants can utilize as a nitrogen source.
- **Plant Uptake**: Ammonia produced by Azospirillum is taken up by plant roots, contributing to their nitrogen nutrition and growth.
2. **Production of Growth-Promoting Substances**:
- **Indole-3-Acetic Acid (IAA)**: Azospirillum synthesizes auxins, particularly IAA, which stimulate root development, lateral root formation, and overall plant growth.
- **Cytokinins**: The bacteria also produce cytokinins, plant hormones that promote cell division, shoot growth, and chlorophyll synthesis.
- **Gibberellins**: Some Azospirillum strains produce gibberellins, which regulate stem elongation, flowering, and fruit development in plants.
3. **Phosphate Solubilization**:
- **Organic Acids**: Azospirillum bacteria secrete organic acids (e.g., citric acid, malic acid) that solubilize phosphate compounds in the soil, making phosphorus more available to plants.
- **Phytase Enzymes**: They also produce phytase enzymes that hydrolyze organic phosphorus compounds, releasing orthophosphate ions for plant uptake.
4. **Biocontrol and Induced Resistance**:
- **Biocontrol Effects**: Some Azospirillum strains exhibit biocontrol activity against plant pathogens by competing for nutrients, producing antibiotics, or inducing systemic resistance in plants.
- **Induced Systemic Resistance (ISR)**: Azospirillum can stimulate plants' defense mechanisms, leading to enhanced resistance against pathogens, pests, and environmental stresses.
5. **Stress Tolerance and Nutrient Uptake**:
- **Drought Tolerance**: Azospirillum inoculation has been associated with improved drought tolerance in plants, possibly due to enhanced root growth and water uptake.
- **Nutrient Uptake**: Besides nitrogen and phosphorus, Azospirillum promotes the uptake of other nutrients (e.g., potassium, iron) by improving root architecture and nutrient mobilization.
Q - Discuss mycorrhiza and its type.
A - Mycorrhiza refers to the symbiotic association between fungi and the roots of plants. This relationship is mutually beneficial, with the fungi aiding the plant in nutrient and water absorption while receiving carbohydrates and other organic compounds from the plant. Mycorrhizae are crucial for plant health, soil fertility, and ecosystem functioning.
Key Features of Mycorrhiza:
Symbiotic Relationship:
Mutual Benefit: Both the plant and the fungus benefit from the association. The plant gains enhanced access to water and nutrients (especially phosphorus), while the fungus receives sugars and other organic substances produced by the plant through photosynthesis.
Nutrient Exchange:
Enhanced Nutrient Uptake: Mycorrhizal fungi increase the surface area for absorption, allowing plants to access nutrients that are otherwise unavailable or difficult to acquire from the soil.
Phosphorus and Nitrogen: These are the primary nutrients provided by mycorrhizal fungi, but they also help in the uptake of other essential minerals such as potassium, calcium, and magnesium.
Types of mycorrhiza
Two main groups of
mycorrhizae are recognized; the ectomycorrhizae and endomycorrhizae, although the rare
group with intermediate properties, the ectendotrophic mycorrhizae.
1. Ectomycorrhiza
The fungal hyphae form a mantle both outside the root and within the root in the
intercellular spaces of the epidermis and cortex. No intracellular penetration into epidermal
or cortical cells occurs, but an extensive network called the Hartignet is formed between
these cells. Sheath or Mantle increases the surface area of absorbing roots and offers
protection to the roots. Hartignet can act as storage and transport organ for P.
2. Endomycorrhizae
Endomycorrhizae consist of three sub groups, but by far the most common are the
Arbuscular Mycorrhizal fungi. Fungi under AM are the members of Endogonaceae and they
produce an internal network of hyphae between cortical cells that extends out into the soil,
where the hyphae absorb mineral salts and water. This fungus do not form an external
mantle but lives within the root. In all forms, hyphae runs between and inside the root cells
which includes,
Ericoid mycorrhiza - Associated with some species of Ericaceous plants
Orchid mycorrhiza - associated with orchid plants
Arbuscular mycorrhiza - associated with most of the plant families
Q - Discuss mode of action of ectomycorrhiza and endomycorrhiza.
A - ### Mode of Action of Ectomycorrhiza (ECM) and Endomycorrhiza (AM)
The mode of action of ectomycorrhiza (ECM) and endomycorrhiza (AM) involves different mechanisms through which they enhance plant growth, nutrient uptake, and stress tolerance. Here’s a detailed discussion on how each type of mycorrhiza operates:
#### Ectomycorrhiza (ECM)
1. **Root Colonization**:
- **Formation of the Mantle**: ECM fungi form a dense sheath of hyphae, known as the mantle, around the root tips of the host plant. This sheath acts as a protective layer and a site for nutrient exchange.
- **Hartig Net Development**: Hyphae penetrate the intercellular spaces of the root cortex, forming a network called the Hartig net. This network facilitates the transfer of nutrients between the fungus and the plant without penetrating the plant cells.
2. **Enhanced Nutrient Uptake**:
- **Phosphorus and Nitrogen**: ECM fungi extend their hyphae into the soil far beyond the root zone, increasing the surface area for absorption and enhancing the uptake of essential nutrients such as phosphorus and nitrogen.
- **Other Minerals**: They also assist in the uptake of other minerals like potassium, calcium, and magnesium.
3. **Water Absorption**:
- **Extended Hyphal Network**: The extensive hyphal network increases the root system's ability to absorb water, enhancing the plant’s drought tolerance.
- **Water Retention**: The mantle can help in retaining water around the roots, providing a buffer against dry conditions.
4. **Protection and Stress Tolerance**:
- **Pathogen Defense**: The fungal sheath acts as a barrier against soil-borne pathogens, and some ECM fungi produce antimicrobial compounds that further protect the plant.
- **Environmental Stress**: ECM fungi can help plants tolerate various environmental stresses, such as heavy metal contamination and extreme temperatures, by improving overall plant health and resilience.
5. **Soil Structure Improvement**:
- **Soil Aggregation**: The fungal hyphae produce glomalin and other substances that bind soil particles together, improving soil structure and stability.
- **Organic Matter Decomposition**: ECM fungi contribute to the decomposition of organic matter, enhancing soil fertility and nutrient cycling.
#### Endomycorrhiza (Arbuscular Mycorrhiza or AM)
1. **Root Colonization**:
- **Penetration of Root Cells**: AM fungi penetrate the root cortical cells, forming intracellular structures called arbuscules (for nutrient exchange) and vesicles (for storage).
- **Formation of Arbuscules**: Arbuscules are highly branched, tree-like structures within the root cells where the exchange of nutrients between the plant and the fungus occurs.
2. **Nutrient Uptake and Transfer**:
- **Phosphorus Mobilization**: AM fungi are particularly effective at mobilizing phosphorus from the soil. They produce enzymes like phosphatases that release phosphorus from organic compounds, making it available to the plant.
- **Nitrogen and Other Nutrients**: They also enhance the uptake of nitrogen, potassium, zinc, and other essential nutrients.
3. **Plant Hormone Production**:
- **Auxins and Cytokinins**: AM fungi produce plant hormones such as auxins and cytokinins, which promote root growth, development, and branching, leading to a more extensive root system.
- **Gibberellins**: Some AM fungi also produce gibberellins, which regulate plant growth and development.
4. **Water Relations and Drought Tolerance**:
- **Enhanced Water Uptake**: The fungal hyphae extend into the soil, increasing the root system's ability to absorb water and improving the plant's drought tolerance.
- **Improved Soil Moisture**: By enhancing soil structure, AM fungi improve soil moisture retention, benefiting plant water uptake.
5. **Induced Systemic Resistance (ISR)**:
- **Defense Mechanisms**: AM fungi can induce systemic resistance in plants, priming them to activate their defense mechanisms more quickly and effectively in response to pathogen attacks.
- **Stress Resilience**: ISR also helps plants withstand abiotic stresses, such as salinity and heavy metal toxicity.
6. **Mycorrhizal Network**:
- **Inter-Plant Communication**: AM fungi form extensive networks that connect multiple plants, facilitating the transfer of nutrients, water, and signaling molecules between plants. This network enhances resource distribution and ecosystem resilience.
Ectomycorrhiza (ECM):
- Forms an external hyphal sheath around roots and penetrates between root cells.
- Enhances nutrient and water uptake, pathogen defense, and soil structure.
- Produces glomalin-like substances, improving soil aggregation.
Endomycorrhiza (AM):
- Penetrates root cells, forming arbuscules and vesicles for direct nutrient exchange.
- Efficiently mobilizes phosphorus and improves nitrogen uptake.
- Produces plant hormones that promote root growth and induce systemic resistance.
- Enhances water uptake, soil structure, and plant stress tolerance.
- Forms extensive mycorrhizal networks, facilitating inter-plant communication and resource sharing.
