Xerophytes
Ecological Niche |
Xerophytes reside in environments which are arid and dry as they do not often see rainfall, or face extremities such as wind. Examples of these environments are desserts, alpine areas or beaches. Xerophytic environments often have shortage of water or where the rate of evaporation is fast, so have adapted in order to survive in such environments. Majority of their adaptations have been made in order to conserve as much water as possible as they receive minimal amounts. As a result of this adaptation, xerophytes often have a very slow growth rate, and even sometimes in periods of extreme drought become dormant. Xerophytes will also be in high competition with other organisms in their environment as it is very scarce, so also have adaptations that protect its water supplies. Some examples of xerophytes are cacti and succulents.
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Adaptations |
![]() Root System Adaptations for Xerophytes
Xerophytic plants have well developed root systems which can either penetrate deep into the soil or penetrate only quite shallow, dependent on the water availability in the environment the xerophyte resides. Xerophytes which have deeper root systems have this adaptation to ensure they absorb all water present. Compared to root systems which are shallow, xerophytes with deeper root systems can collect water that is below the shallow surface of the soil. This adaptation is crucial for xerophytes in environments where there is not a lot of access to water. One example of this is Acacia Tree (pictured) which has roots that have been known to stretch over 8 metres below the surface. If Acacia Trees had root systems that were shallow and undeveloped, they would not be able to sustain life as their roots are how they obtain water, in comparison to a hydrophyte such as a water-lily which has an undeveloped root system only used for anchorage. By having this adaption xerophytes can maintain optimum water balance by absorbing water in the soil which is needed for successfully carrying out life processes, for example photosynthesis and respiration. Xerophytes with more shallow root systems that are undeveloped may live in an environment where there is a high lack of water, therefore do not waste what little energy they have growing deep roots as it is of no use to them. Xerophytes which have this type of root system can take advantage of rainfalls by being able to quickly collect available water as it enters the soil. One example of a xerophyte with this type of root system is the Haworthia emelyae Plant (pictured)source: http://www.cactus-art.biz/note-book/Dictionary/aaa_plant/Hawhortia_emelyae_v_major_cv_Hakuma_roots_180.jpg). This root system which is shallow yet widespread helps it to survive in it’s environment as the roots allow for absorption of water via osmosis. Stem Adaptations of Xerophytes Xerophyte stems provides the plant with structure and support and is also where all water the plant obtains is stored. The stem is adapted to be suitable for holding the weight of the plant as compared to a hydrophyte which has a thin stem as it is supported by water, a mesophyte does not live in an aquatic environment. Furthermore if a xerophyte had the stem of a hydrophyte, water could easily diffuse in and out as the thick stem of a xerophyte prevents this from happening. Xerophyte stems are also able to expand quickly in the event of a sudden rainfall or flooding in order to store the most amount of water possible as the tissue is the stem is quite porous. This adaptation also allows for water to be transported around the plant in dry conditions. Xerophyte live in environments where competition for water is fierce. Their ability to store vast amounts of water in their stems means that a thirsty animal may try and bite the plant in order to obtain water. Furthermore, any damage to the plant could lead to the plant’s water supply being threatened as this would expose it to the extremities as the protective outer layers of the plant would be damaged. This damage may lead to the death of the plant as xerophytes do not have regular access to water and the amount of water lost, even though it may be small in quantity, may be deadly. In order to protect itself, xerophytes have adaptations such as thorns, hair or spines, which act as defensive mechanisms. These stems prevent damage from animals which may try and obtain water from the plant as well as provide shade for the stem which reduces transpiration from the stomata. Waxy Cuticle Xerophytes have a thick waxy cuticle on their stems as well as on the epidermis of their leaves if they have any. This cuticle helps to reduce the amount of water lost through transpiration and evaporation, which is common in environments where xerophytes live due to factors such as extreme heat and wind. This adaptation ensures that as much water as possible is preserved as xerophytes often live in environments where water is scarce. Furthermore, the waxy cuticle also helps to reflect sunlight off the plant as the cuticle itself is quite shiny. This helps to keep the plant cool as well as reduce evaporation caused by sunlight. One example of a plant with this adaptation is the Aloe plicatilis (pictured). This plant has a thick, waxy cuticle which is shown as the leaves looks fleshy and matte. This helps to reduce the amount of water lost by evaporation as Aloe plicatilis tend to live in environments where water evaporates quickly. However this cuticle may act as a limitation as gases which diffuse through the stomata may not be able to do so through the cuticle which is quite thick. Stomata Xerophytes often have a reduced number of stomata which are in ‘sunken pits’ in the epidermis, creating a microclimate. These sunken pits also often have hair growing from them which helps to keep the area around the stomata cool as well as trap water. This helps to reduce the amount of water lost through evaporation by trapping moist air around the stomata and reducing the concentration gradient. Furthermore, this also acts as a shield from the elements, such as wind which can also increase the rate of evaporation. Some xerophytes, for example, cacti do not have leaves and instead have hair or spines in the place of leaves. This helps to create shade for the sunken pits where the stomata are, as well as offer the plant protection from animals which may damage to it by trying to access its water supply. Therefore by having a decreased amount of stomata, xerophytes are able to maintain water balance. Xerophytes have also adapted to suit their environment by only opening their stomata during the night, and closing them during the day as it is cooler at night and hotter during the day.This helps to conserve what little water these xerophytes get as in the heat of the day is when the most amount of water would be lost through transpiration. Furthermore, night time is also when these xerophytes undergo CAM (crassulacean acid metabolism) photosynthesis. In the daytime is where sunlight collected by the chloroplasts is turned into solar energy and then stored, whereas, at night time the stomata open in order to collect carbon dioxide. Thus the plant can use these organic acids to photosynthesise. |