1. Define mycorrhizae and explain their types.
Answer:
Definition: Mycorrhizae are symbiotic associations between fungi and plant roots that enhance nutrient and water uptake in plants while providing carbohydrates to fungi.
Types:
- Ectomycorrhizae:
- Form a sheath around plant roots.
- Hyphae penetrate the root cortex but not the cells.
- Common in trees like pine and oak.
- Endomycorrhizae (Arbuscular Mycorrhizae):
- Fungi penetrate root cells, forming arbuscules.
- Found in most agricultural crops.
2. How do mycorrhizae enhance phosphorus uptake in plants?
Answer:
Mycorrhizae increase the root surface area by forming a network of hyphae, which explore soil regions beyond the plant root’s reach. This allows efficient absorption of immobile nutrients like phosphorus, which is critical for plant growth and development.
3. Discuss the role of mycorrhizae in nutrient cycling.
Answer:
Mycorrhizae contribute to nutrient cycling by:
- Breaking down organic matter.
- Mobilizing nutrients like nitrogen, phosphorus, and micronutrients.
- Enhancing the availability of nutrients for plants.
Their extensive hyphal network connects soil and plant systems, facilitating nutrient flow across ecosystems.
4. Explain the mutual benefits of mycorrhizal associations.
Answer:
Plants Benefit:
- Enhanced nutrient and water absorption.
- Improved resistance to pathogens.
- Increased tolerance to environmental stresses.
Fungi Benefit:
- Access to carbohydrates produced by the plant through photosynthesis.
- A stable habitat in the plant root system.
5. What are arbuscules, and what role do they play in plant nutrition?
Answer:
Arbuscules are branched, tree-like structures formed by arbuscular mycorrhizal fungi inside root cells. They facilitate nutrient exchange by increasing the contact area between fungal hyphae and plant cells, ensuring efficient transfer of phosphorus and other nutrients to the plant.
6. How do mycorrhizae improve drought tolerance in plants?
Answer:
Mycorrhizae enhance drought tolerance by:
- Increasing root water absorption through their hyphal network.
- Storing water in fungal structures.
- Regulating osmotic balance within plant cells.
This adaptation is crucial for plants growing in arid environments.
7. Describe the role of ectomycorrhizae in forest ecosystems.
Answer:
Ectomycorrhizae:
- Form extensive networks around tree roots.
- Facilitate the uptake of nutrients like nitrogen and phosphorus.
- Enhance soil structure through fungal secretions.
- Promote biodiversity by supporting tree growth and interconnections between species.
8. How do mycorrhizae assist in saline soil conditions?
Answer:
In saline soils, mycorrhizae help by:
- Enhancing water uptake, reducing salt stress.
- Sequestering toxic ions.
- Modulating plant hormonal responses to salinity.
These functions allow plants to survive and grow in high-salt environments.
9. Discuss the ecological significance of mycorrhizae in sustainable agriculture.
Answer:
In sustainable agriculture, mycorrhizae:
- Reduce the need for chemical fertilizers by improving nutrient uptake.
- Enhance soil fertility and structure.
- Promote crop yield and resilience.
- Support intercropping systems by connecting different plants to shared nutrient resources.
10. What is the role of vesicles in mycorrhizal fungi?
Answer:
Vesicles are storage structures in mycorrhizal fungi that store lipids and nutrients. They act as reservoirs to sustain the fungus and the plant during nutrient shortages, ensuring long-term survival.
11. Explain how mycorrhizae protect plants from soil pathogens.
Answer:
Mycorrhizae protect plants by:
- Forming a physical barrier around roots.
- Competing with pathogens for space and nutrients.
- Producing antifungal compounds.
- Enhancing plant immune responses.
12. What is glomalin, and how does it benefit soil health?
Answer:
Glomalin is a glycoprotein secreted by arbuscular mycorrhizal fungi. It benefits soil health by:
- Binding soil particles, improving structure.
- Enhancing water retention.
- Sequestering carbon, contributing to soil fertility and sustainability.
13. How do mycorrhizae influence plant diversity in ecosystems?
Answer:
Mycorrhizae promote plant diversity by:
- Equalizing nutrient availability, allowing various species to thrive.
- Enhancing stress tolerance, enabling plants to survive in marginal habitats.
- Facilitating coexistence through shared fungal networks.
14. Describe the role of mycorrhizae in reforestation efforts.
Answer:
Mycorrhizae support reforestation by:
- Improving nutrient and water uptake in saplings.
- Enhancing resistance to harsh soil conditions.
- Promoting survival and growth of trees in degraded lands.
Their presence ensures ecosystem recovery and biodiversity restoration.
15. How do mycorrhizae reduce heavy metal toxicity in plants?
Answer:
Mycorrhizae mitigate heavy metal toxicity by:
- Sequestering metals within fungal hyphae.
- Preventing the uptake of toxic concentrations.
- Enhancing plant detoxification mechanisms.
16. Explain the role of mycorrhizae in orchid seed germination.
Answer:
Orchid seeds lack endosperm and depend on mycorrhizal fungi for nutrients during germination. The fungi provide essential carbon and nutrients, enabling seedling establishment.
17. How do mycorrhizae contribute to soil aggregation?
Answer:
Mycorrhizae secrete glomalin, which binds soil particles into aggregates. This improves soil porosity, aeration, and water retention, fostering healthy plant growth.
18. Discuss the limitations of mycorrhizal associations.
Answer:
Limitations:
- Ineffectiveness in high-phosphorus soils, reducing plant dependency.
- Limited colonization in certain plant species like Brassicaceae.
- Potential parasitism under nutrient-rich conditions, leading to reduced plant growth.
19. What is the role of mycorrhizae in carbon sequestration?
Answer:
Mycorrhizae enhance carbon sequestration by:
- Facilitating plant growth and photosynthesis.
- Storing carbon in fungal biomass and glomalin.
- Improving soil organic carbon levels, contributing to climate change mitigation.
20. Compare and contrast arbuscular and ectomycorrhizae.
Answer:
| Aspect | Arbuscular Mycorrhizae | Ectomycorrhizae |
|---|---|---|
| Root Interaction | Penetrate root cells | Form external sheath |
| Host Plants | Agricultural crops, grasses | Trees like pine, oak |
| Nutrient Absorption | Phosphorus | Nitrogen and phosphorus |
| Ecosystem | Grasslands, croplands | Forest ecosystems |
Both types play crucial roles in plant nutrition and ecosystem health.
This module serves as a comprehensive guide to understanding the role of mycorrhizae in plant nutrition.
