Plant Adaptation in Desert Conditions

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Drought conditions include constant dry weather, which causes the area to get less amounts of rain over many months and years, because of this, sunlight is over abundant and water is scarce. Climate change accelerates droughts because greenhouse gases are increasingly released into the atmosphere causing air temperatures to rise. Moisture then evaporates from land, lakes, rivers and other water bodies. This warmer temperature causes increased evaporation in soils and causes plant life to suffer. 

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During drought seasons plants have a goal of maximizing the conditions they are already experiencing. Plants in arid conditions have smaller leaves no leaves at all this causes there to be less stomata so water loss is limited through transpiration. Leaves are also modified into spines or spikes they allow shade for the plant this reduces evaporation of water from the surface of the plant. To survive in arid, desert and drought environment plants also have a succulence feature this allows them to store large amounts of water in their vacuoles, this allows them to act as a storage system of ions and water. 

The Sahara Desert and the Arabian Desert display the characteristics of drought prone environments. This includes a very hot climate with temperatures exceeding 40°C, the climate being very dry with less than 250 mm of rainfall a year.The Sahara Desert embodies drought prone characteristics which includes it being dry, arid with extremely hot temperatures being in range of 50 – 58°C and minimal vegetation. The main cause of these characteristics within the Sahara Desert is due to it being  a dry subtropical and a dry topical desert. The dry subtropical nature is caused by constant high-pressure cells over the tropic of cancer and the dry tropical nature which is caused by a stable continental air mass and an unstable marine air mass. 

The Arabian Desert also shows drought prone environments, this is demonstrated by it receiving very little rainfall annually below 33 millilitres and only having 15% of air humidity as well as this its temperatures during the day being extremely high make it inhospitable. Ochsenwald, 2017) lying between the north of the tropic of cancer making it a tropical desert because of this the heat is intense and reaches temperatures of 55°C. 

The structural adaptations of a plant include leaf shape, large leaves, spines, shallow root systems, succulence, spikes/spines. Leaf shape is a structural adaptation because, they maximise photosynthesis by capturing as much light energy as possible, this is important for a plants survival because they use sunlight to make glucose to survive. Spines are another structural adaptation because they help cactus preserve water and protection from predators the spines act as a deterrent. This is important for a plant’s survival because, the spines preserve water by remaining metabolically inactive and allow water vapor from the atmosphere to condense onto the spines and rundown the surface of the plant to be absorbed by the roots. Shallow roots help cause structural adaptation by allowing the plant to absorb as much water as possible when it rains and allowing small amounts of moisture that occur on the surface due to fog. 

Succulence is another structural adaptation because it allows the plant to optimize water storage it also has a low surface area to volume ratio this ensures minimal transpiration water loss. Phototropism states that a plant bends and grows towards a light source, its shoots move towards light and its roots away. This is a behavioural adaptation because since the plant shoots are positively phototropic and the roots are negative phototropic, their leaves are exposed to the light to allow photosynthesis because the shoots are growing upwards. Due to the plant being anchored into the soil, the roots are positively geotropic but the shoots negatively geotropic, this means that the roots growing downwards anchor into the ground and receive the vital nutrients they need form the soil. This is important for a plant’s survival and development because this phototropic and geotropic action ensure the plant still recieves sunlight in order to photosynthesis even when light is in scarcity this includes a plant wrapping around walls. Plants have evolved to endure drought stress this has manifested in ways such as drought escape, dehydration avoidance and dehydration tolerance. 

Drought escaping plants have a mechanism that allows them to complete their life cycle before a lack of water in the environment arises because of this they are unaffected by the drought. These types of plants moderate their vegetation, flowering and growth according to water availability they have two mechanisms which make this possible rapid phenological development and development plasticity. Development plasticity is when the plant exhibits very little growth during drought season with less vegetation and flowering but during wet seasons they grow rapidly and make large amounts of seeds.

Dehydration avoidance is another mechanism which responds to drought stress and this includes leaf rolling. Leaf rolling occurs because plant moisture is decreasing the rolling of the leaf promotes dehydration avoidance because less surface area is exposed and transpiration is reduced. A thick waxy cuticle reduces the rate of water loss from the leaf surface as a result dehydration is avoided because the plant still remains hydrated. 

In conclusion, the understanding of drought escape, dehydration avoidance and dehydration tolerance, is important for increasing the production of food crops because without it the supply for food will be significantly less than the demand. An example of this includes crops such as rice, wheat and soybeans because they are adapted to survive dry conditions better this is because they have a mechanism called CAM. This happens when photosynthesis is separated into two times a day, during daytime the stomata is closed to reduce evaporation causing them to open their stomata at night-time to take up carbon dioxide, because there is no sunlight the plant performs the Calvin cycle to produce sugar. 

29 April 2022

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