The correct option is (d).
Explanation
Mycorrhiza is a symbiotic association between fungi and the roots of vascular plants. This relationship is extensively utilized in biotechnology and forestry for the rehabilitation of degraded ecosystems because it significantly enhances plant survival and growth in adverse soil conditions.
Statement-wise Analysis:
- Statement 1 is Correct: The fungal hyphae extend extensively into the soil, acting as an extension of the root system. This significantly increases the absorptive surface area, allowing the plant to access water and nutrients (particularly Phosphorus) from a much larger volume of soil. This mechanism is crucial for enabling plants to resist drought.
- Statement 2 is Correct: Mycorrhizal fungi help plants adapt to chemical stresses in the soil. They assist in regulating ion uptake and can immobilize toxic elements, enabling plants to tolerate extremes of pH (both high acidity and alkalinity) and salinity, which are common in degraded sites.
- Statement 3 is Correct: The fungal association provides a protective barrier around the roots and stimulates the plant's immune system. Furthermore, beneficial mycorrhizal fungi compete with harmful microbes for resources, thereby helping the plant resist disease infestation caused by soil-borne pathogens.
Key Takeaway:
Mycorrhizal biotechnology is a vital tool in ecological restoration as it enhances nutrient and water uptake, confers tolerance to abiotic stresses (drought, pH extremes), and provides biotic resistance against pathogens.