Question

Mycorrhiza in higher plants helps in
A. Absorption of phosphates and water from soil
B. $N_2$ fixation
C. Water supply and resistance against diseases
D. Both A and C

Answer 1

The association between the roots and fungi are called mycorrhiza. These are survival mechanisms that are needed for the development of the plant in adverse conditions. A Large number of native desert plants are hosts to these fungi and they cannot survive without them.

Complete answer:
When plants live in challenging locations, they often develop to survive in adverse conditions. These include morphological characteristics like narrow leaves for reducing water loss, reducing plant growth, developing tolerance to high salts and low levels of nutrients. One of the useful survival mechanisms involves creating mutually beneficial relationships between plants of roots and soil- borne organisms such as fungi and bacteria.
Mycorrhiza is a mutual symbiotic association between fungus and roots of higher leguminous plants. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere which is its root system. It plays an important role in plant nutrition, soil chemistry and biology. Plant roots are sites for the fungi to anchor and produce hyphae. The roots provide essential nutrients for the growth of the fungi. In return, these fungal hyphae act as a root system for the plants.
Mycorrhiza are essential in areas where there is deficiency of water and nutrients. Larger roots help to attain additional moisture and nutrients. This is particularly important for the uptake of phosphorus, one of the major nutrient needs for the plant. Plants make substances such as sugars by the process of photosynthesis and supply it to the plant waste and mineral nutrients such as phosphorus taken from the soil.
Desert plants interact with the organisms that are present in the soil. Many of them are used to fertilise plants by "fixing nitrogen" that are later taken up by the plant as a nutrient. The most common association on roots is as nodules. These nodules are small outgrowths on the roots. The microbes such as Frankia, also produce nitrogen - fixing nodules on the roots of non- leguminous roots. When mycorrhizae are present, the number and vitality of these nitrogen fixers increase. As a result, the plant's health is beneficial for plants.

So, the correct answer is option D, Both A and B.

Note-
The desert soil already has mycorrhizal fungi in small amounts. Even without inoculation, spores can be found in these plants at many places. If host plants are grown on other plants, both thrive but mycorrhizal continues to survive even after the original host is not present.