Question

Describe the physiological and anatomical characteristics that confer drought tolerance on plants. Which of the following is more suitable for Australia's climate? explain your answer

Answer 1

Drought tolerant plants have many physiological and anatomical adaptations to survive. The biomass production and functions will take place neturally even in the dry conditions. They have the charecteristics like,

• Reduction in leaf area and samll leaves - by reducing the leaf area the transpiration loss can be reduced. The area can be reduced by the rolling and curling of leaves whuch will reduce the exposure to sunlight. eg: maize,grasses. The size of the leaves will be small like in Oyster Bay Pine.
• Early closure of stomata - The stomata will be opened in the morning for a lesser time and will remain closed the whole day and the photosynthesis will take place with least loss of water. eg: wheat,oats.
• Waxy leaf surface - waxy leaves is the sign of thick cuticle and also spine development in leaves will reduce the transpiration. eg: safflower.
• Silver leaf helps to reflect sunlight thus by keeping the plant cool. eg: Eremophila glabra.
• Increased photosynthetic efficiency- These plant species have a high rate of carbohydrate assimilation for given stomatal opening higher temperature and light optimum. eg: maize.
• Deposits of lipid layers - The lipids present in the leaf surfaces will reduce the transpiration losses. eg:soyabean
• Low rate of cuticular transpiration - Thick cuticle results in low rate of transpiration eg:cactus.
• Location of stomata - stomata located on cavity or depressions will reduce the doirect contact of stomata with the wind thus by reducing transpiration. and also more stomata will be present in the lower leaf surfaces.
• Number of stomata - The number of stomata will be less to avoid transpiration.
• Effect of awns - The awned varieties of wheat, barley  can thrive well in stress conditions because the awns contain chloroplast and stomata so it can continue photosynthetic activites even when the leaf stomata is closed.
• Efficient root system- the efficient root system helps in the accelarated water uptake. The roots will be extensive, deeper, ability of the root to grow toward water and to penetrate in soil and also have high osmotic pressure etc. Also the roots acts like tubers which helps the plant to survive drought.
• Presence of phyllodes instead of leaves - phyllode is a flattened leafstalk that functions like a leaf which minimizes water loss. eg : Acasia.
• Presence of succulance- this is the thick and fleshy leaves of stem which will retain water for long time. eg : clavata
• Presence of lignotuber - it is a wooody swelling at or just below ground level and the food id stored for hard times. eg: Eucalypyus rossii.

Australian climate have different climatic zones and it is due to the size and the sinking air of the subtropical high pressure belt. The climate is variable so it experiences frequent droughts lasting a long time. so the plants wants to be adapyive to the environment.The native varieties of plants have the charecteristic like presence of succulance, lignotuber, silver leaves, thick waxy coating on leaves and smaller leaves, presence of phyllodes, thick and fleshy leaves and stem, presence of tubers and enlarged roots etc