Adaptation Mechanisms of Crops in Response to Climate Change

Adaptation Mechanisms of Crops

We know that to survive in unfavorable environment, plant adjust themselves by different physiological and bio- chemical changes. The technique of this adjustment is known as adaptation. Based on the knowledge about adaptation mechanisms of crops, the agricultural scientists have been developed various crop varieties which are suitable to be cultivated under unfavorable condition. We shall discuss the adaptation mechanisms of crops to drought, salinity, submergence or flood etc. unfavorable or adverse environment in this chapter.

A. Adaptation mechanisms of crops to drought

We have learnt about drought in previous. There is a lack of moisture in soil, low water vapor in air, high temperature and high intensity of sunlight under drought condition. In this condition crop plants survive through drought escaping and drought prevention.

1. Drought escaping:

The easiest way of adaptation of crops in drought is drought escaping. The completion of life cycle during the period from starting of rainfall to starting of drought to getaway themselves from drought is called drought escaping. There are some short durational plants in desert regions. Seeds of these plants germinate just after rainfall and complete their life cycle within 2 months. 

There are some types of crops of which life cycle is short. There are some varieties of millets which mature within 60 days of germination. The early varieties of some crops can escape from one or two drought as they become matured within short duration. If the duration needs for flowering, fruit setting and maturity is short, they can escape from drought, such as cowpea requires 17- 20 days for flowering to maturity. Therefore, by cultivation cowpea in drought- prone areas, the crop can be harvested before appearing drought.

2. Drought prevention:

The mechanism of surviving crop plants under drought condition is called drought prevention. The drought prevention of crop is again divided into two categories, such as- a) drought tolerance b) drought avoidance. Now we shall discuss the mechanisms of drought tolerance.

a) Mechanisms of drought tolerance:

The survival ability of crop plants with low water balance in the plant body under condition of drought is called drought tolerance. These crops show normal growth and bear flowers and fruits after disappearing of drought condition. The mechanisms of drought tolerance of crops are discussed below:

1. R�sistance to cell dehydration: This type crop store adequate amount of solutes in the cell under drought condition. Consequently high osmotic pressure exists in the cell. Water does not dry out from the cell and the cell does not become flaccid. This condition is found in cotton during drought.
2. Thick cell membrane: In some crops, leaf has thick cell membrane; consequently the leaf does not wilted, if the cell water is less in leaf.
3. Starvation: Some plants lesser their rate of photosynthesis under drought condition. In this condition although the leaf cells become wilted, the guard cells deposited various solutes in the cells and maintain turgor pressure, make entrance of lower amount of carbon dioxide to continue limited photosynthesis. Thus under drought, plants just survive under drought condition.
4. Protein and proline accumulation: Due to the effect of drought, the protein is broken down and takes part in different bio- chemical activities. The higher storage of protein in plant body helps in drought tolerance. Again, by breaking down protein, various types of toxic substances are produced. For that reason, some plants produce a chemical substance named proline which lessers the toxicity level and makes the crop plants drought tolerant.
5. Absence of vacuole: The differences in drought tolerance in crop plants are found due to variations in morphology. The plant parts in which there is no vacuole, they can tolerate drought, such as- due to drought although leaves of some plants die, leaf bud does not die. The leaf buds tolerate drought and started to grow after disappearing of drought.
6. Dormancy: Above ground parts of many plants die under drought condition but the under-ground parts remain viable in dormant state as tuber/ bulb/ rhizome etc. These germinate under favorable condition.

b) Mechanisms of drought avoidance:

We learnt previously that there are two mechanisms of drought prevention in crop, such as- drought tolerance and drought avoidance. The main drought avoidance mechanisms of crop plants are described below:

1. Control of stomata: Some plants face the drought by lowering loss of water caused by transpiration by controlling the opening and closing of stomata. For example, barley and other tall varieties of wheat crop open stomata in the morning for few times and rest of the time remain closed. Again, many crop plants lower their size of stomata, close stomata, if there is lack of water in cells and increased environmental temperature. Most of the varieties of bean avoid drought this way. Again, leaves of many crop plants contain stomata in lower amount, stomata remains in the leaf whole (sunken stomata). Therefore, transpiration becomes lower and thus water is conserved.
2. Control of transpiration: Many plants deposit lipids on the upper surface of the leaves and lower the transpiration rate when they remain under drought condition; such as- soybean crop. Again many plants make a layer on the upper leaf surface by wax or densely hair to lower transpiration.
3. Decreasing leaf size: Many plants lower transpiration under drought condition by decreasing leaf size; such as cow pea. Many plants decrease leaf size by burning leaf edge or leaf tip.
4. Leaf shedding: Many plants lower transpiration by shedding lower older leaves under severe drought condition.
5. Increasing photosynthetic efficiency: Although some plants lower transpiration by controlling stomata, they photosynthesize more by in taking little amount of carbon dioxide through stomata. It is found in maize, sugarcane etc. crops.
6. Efficient root system: Some plants face drought condition by uptaking more water by increasing root length, root number and root density; such as- this tendency is found in many varieties of maize, cotton and wheat. If the higher depth and density of root are present in an single crop, this crop becomes more tolerant to drought; such as- Jower and Bajra. Again, groundnut, Pigeon peas are deep rooted and are drought tolerant.
7. Leaf rolling and leaf curling: Many cereal crops; such as- jower, millets, also curl their leaf under drought condition except decreasing leaf size. Again, some crop plants decrease the sunlight absorbing area of leaf by curling their leaves. Consequently, due to the decrease of transpiration loss of water they adapt drought condition.
8. Changes in leaf orientation: Many plants change their leaf orientation towards the sunlight or at straight under drought condition. Consequently, water is saved by decreasing transpiration. Many dicotyledonous crops including groundnut, cotton and cowpea avoid drought by this process.

B. Adaptation mechanisms of crops to salinity

We learnt about saline condition, crop production techniques under saline condition in class viii. The crops are divided into two categories based on the response to salinity; such as a) Halophytes- gol pata, keora and b) Glycophytes- sugarbeat, bean, cotton. The halophytes plants can germinate in saline condition and can complete their life cycle there but glycophytes can do this.

The concentration of soil water of saline soil is high as higher amount of calcium and sulfate salts of sodium, calcium, magnesium etc. are present in water in soluble form. To survive crop plants in this condition, the cell sap concentration of plants has to be higher compared to the concentration of soil water. If not higher, the plants cannot absorb water and nutrient from soil; on the other hand plants become wilted due to loss of water. In this condition, to maintain turgidity of plant cell, it is necessary to collect various ions (K+, Na+) from soil to overcome this obstacle made by salinity. Thus the excessiveness of ion occurs in plant body. But salinity tolerant plants control the uptake of ions. Leaves some plant species have salt net through which they can drain out excess ion. Again some species enlarge their leaf size and thereby lower the salt concentration in their body. In some species there is special arrangement in leaf to store excess ion.

There are some species that do not uptake ion under salinity condition but they take other technique. These plants store organic substances in vacuole to maintain turgidity of root cell. The volume of vacuole of these types of plants is 95% of their total cell volume. Among the organic substances stored in the vacuole, the photosynthetic product is higher.

C. Adaptation mechanisms of crops to submergence or flood

Besides aquatic plants, most of the plants cannot survive under flood or submergence or under saturated condition of soil water. In this condition, the plant roots cannot respire due to the lack of oxygen in soil. The quicker the soil or soluble oxygen in soil water become empty, the quicker the plants die. Rice is a water loving plant. Rice plant has aerenchyma tissue. This tissue has a lot of air spaces. Oxygen is stored in these air spaces. Consequently, if rice plants do not go under water fully, they can survive under flood or submergence and give good yield. But if submerged for long time, they die. The plant height of deep water rice increases with the increase of flood water. The internodes of the plants of such rice varieties possess a kind of meristematic tissue which is divided quickly with the increase of the height of flood water and thereby increase plant height and face flood. Again the tall varieties of rice can escape from flood due to their height.

D. Adaptation mechanisms of crops to high temperature

The rate of photosynthesis and respiration is decreased at high temperature. The rate of decrease in photosynthesis is more compared to that of respiration. In this condition, the protein of crop plants become degraded and water loss occurs. At high temperature, special non- degradable protein is formed in the plants that are tolerant to high temperature. The high temperature tolerant plants can remove the broken protein from the body.