Mesophytes
In mesophytes, the stomata are generally found on the underside of the leaf. Since water evaporates upwards, having the majority of stomata on the underside of the leaf will mean water is trapped under the leaf, which reduces water loss [13]. By ensuring that less water is lost through the stomata, it will enable the plant to have the stomata open more often. In doing so, gas exchange of carbon dioxide in and oxygen out during the process of photosynthesis, will also be more efficient. During times when the conditions are windy, the stomata will close to reduce water loss, as in windy conditions, the water vapour is blown away so the diffusion of water vapour out of the leaf occurs faster.
In the temperate conditions mesophytes are found in, water availability is not a major problem. This has resulted in many plants, especially plants which are lower in height, have big leaves. Although this provides a limitation to the plant, in which having large leaves will increase the rate at which transpiration is occurring, this adaptation will increase the surface area for light absorption [13]. Due to water availability being sufficient, plants have increased the size of their leaves to receive more light for photosynthesis, which allows them to produce glucose and oxygen at a faster rate, allowing them to carry out their life processes and have better chance of survival.
It has also been found that taller plants have relatively smaller and more spaced out leaves. This is because these plants receive the maximum amount of sunlight due to their height. Therefore there is no need to have large leaves as the amount of light they receive is sufficient. By reducing the size of their leaves, this will reduce the surface area for water evaporation, and minimize the amount of osmosis occurring. This can then enable to the plant to conserve its water supply, and slow down the rate of transpiration.
The majority of leaves found on mesophyte plants have a waxy cuticle. The cuticles provides a protective layer, and also stops water from evaporating easily through the top of the leaf. This reduction in water loss also contributes to the water balance of plants, and will help the plant to survive better.
Leaf hairs can also be found on some mesophytes. These hairs trap water as it evaporates, and condenses it around the stomata. This will then create a micro-climate, on the underside of the leaf, which will reduce the concentration gradient between the inside and the outside of the plant. Therefore, less transpiration is occurring, so water loss is reduced.
In the temperate conditions mesophytes are found in, water availability is not a major problem. This has resulted in many plants, especially plants which are lower in height, have big leaves. Although this provides a limitation to the plant, in which having large leaves will increase the rate at which transpiration is occurring, this adaptation will increase the surface area for light absorption [13]. Due to water availability being sufficient, plants have increased the size of their leaves to receive more light for photosynthesis, which allows them to produce glucose and oxygen at a faster rate, allowing them to carry out their life processes and have better chance of survival.
It has also been found that taller plants have relatively smaller and more spaced out leaves. This is because these plants receive the maximum amount of sunlight due to their height. Therefore there is no need to have large leaves as the amount of light they receive is sufficient. By reducing the size of their leaves, this will reduce the surface area for water evaporation, and minimize the amount of osmosis occurring. This can then enable to the plant to conserve its water supply, and slow down the rate of transpiration.
The majority of leaves found on mesophyte plants have a waxy cuticle. The cuticles provides a protective layer, and also stops water from evaporating easily through the top of the leaf. This reduction in water loss also contributes to the water balance of plants, and will help the plant to survive better.
Leaf hairs can also be found on some mesophytes. These hairs trap water as it evaporates, and condenses it around the stomata. This will then create a micro-climate, on the underside of the leaf, which will reduce the concentration gradient between the inside and the outside of the plant. Therefore, less transpiration is occurring, so water loss is reduced.
Hydrophytes
In hydrophytes, the stomata can be found in various amounts on different sides of the leaf. In the case of hydrophytes that float on top of the water, such as lilies, the stomata are found on the top of the leaf, in contrast to mesophytes. This is because having more stomata on the upper side of the leaf will increase the amount of carbon dioxide entering the leaf for photosynthesis, as the stomata are exposed to the air rather than the water. This will mean more photosynthesis can occur, resulting in the plant being able to produce nutrition and carry out its life processes faster. The stomata of hydrophytes are always open as well. Since water loss is not a problem, the rate at which transpiration is occurring does not need to be reduced, and having open stomata will increase gas exchange which is a limiting factor for hydrophytes.
As hydrophytes live in conditions where water is extremely abundant, the biggest problem for these plants is the supply of essential gases, carbon dioxide and oxygen. In the mesophyll layer of their leaves, large air spaces can be found called lacunae. These air spaces allow for efficient gas exchange, and also provide buoyancy for the plant if they float on top of the water.
Some hydrophytes, such as Impatiens glandulifera also have hollow stems. This increases the plants buoyancy to float on the surface of the water and will allow for carbon dioxide to enter, and for oxygen to leave the cell for photosynthesis. Therefore this will help the plant to carry out life processes and survive.
No waxy cuticle, or a very thin one, can be found on the leaves of hydrophytes [15]. Due to the excess of water available to them, there is no need for a waxy cuticle, since reducing water loss is not a factor these plants have needed to adapt to. In fact, water is required to evaporate quickly to manage the excess amount of water in their environment, so a waxy cuticle is not needed.
There is also the absence of a vascular system in hydrophytes. As water and dissolved minerals can be gained directly through direct diffusion into the plant, hydrophytes do not have any need for a vascular system due to the environment they are living in. Hydrophytes are also not lignified. As they live in or on top of water, they will constantly be moving. Consequentially, there can be large waves or some tidal movement, so lignified plants will tend to break in these conditions. Hydrophytes do not require the support from the xylem and phloem tubes since the water provides any support required. Therefore, the vascular system can be under developed, and this, as well as the plants not needing to be lignified, will allow hydrophytes to focus more on water balance, and sufficient gas exchange, allowing them to further increase their chances of survival.
It also tends to be that roots in hydrophytes are reduced, or they are absent. Since minerals are dissolved in water around the plant, and the water can be taken in through direct diffusion, there is generally non need for these plants to have roots. Some plants, however, such as weed eel grass, require an extensive root system due to the strong tidal activity they experience, and will require anchorage. On the other hand, some plants have no roots to take advantage of any currents for mobility, and allow for them to access a wider variety of resources to aid their survival [6].
As hydrophytes live in conditions where water is extremely abundant, the biggest problem for these plants is the supply of essential gases, carbon dioxide and oxygen. In the mesophyll layer of their leaves, large air spaces can be found called lacunae. These air spaces allow for efficient gas exchange, and also provide buoyancy for the plant if they float on top of the water.
Some hydrophytes, such as Impatiens glandulifera also have hollow stems. This increases the plants buoyancy to float on the surface of the water and will allow for carbon dioxide to enter, and for oxygen to leave the cell for photosynthesis. Therefore this will help the plant to carry out life processes and survive.
No waxy cuticle, or a very thin one, can be found on the leaves of hydrophytes [15]. Due to the excess of water available to them, there is no need for a waxy cuticle, since reducing water loss is not a factor these plants have needed to adapt to. In fact, water is required to evaporate quickly to manage the excess amount of water in their environment, so a waxy cuticle is not needed.
There is also the absence of a vascular system in hydrophytes. As water and dissolved minerals can be gained directly through direct diffusion into the plant, hydrophytes do not have any need for a vascular system due to the environment they are living in. Hydrophytes are also not lignified. As they live in or on top of water, they will constantly be moving. Consequentially, there can be large waves or some tidal movement, so lignified plants will tend to break in these conditions. Hydrophytes do not require the support from the xylem and phloem tubes since the water provides any support required. Therefore, the vascular system can be under developed, and this, as well as the plants not needing to be lignified, will allow hydrophytes to focus more on water balance, and sufficient gas exchange, allowing them to further increase their chances of survival.
It also tends to be that roots in hydrophytes are reduced, or they are absent. Since minerals are dissolved in water around the plant, and the water can be taken in through direct diffusion, there is generally non need for these plants to have roots. Some plants, however, such as weed eel grass, require an extensive root system due to the strong tidal activity they experience, and will require anchorage. On the other hand, some plants have no roots to take advantage of any currents for mobility, and allow for them to access a wider variety of resources to aid their survival [6].
Xerophytes
In xerophytes, the stomata can often be found in sunken pits, such as in the Crassula and Ammophila plants. Having the stomata in pits will shield them from the wind. When wind blows on the stomata, the water is immediately blown away, so will result in transpiration occurring faster, therefore meaning protection from the wind will reduce water loss in the plant.
The roots of xerophytes have adapted in a range of different ways, depending on the ecological niche of each plant. The roots can sometimes be found close to the surface of the ground. This allows plants to take advantage of any moisture absorbed by the soil, as a result of some condensation occurring overnight. On the other hand, some plants like the chaparral plants and marram grass have roots which will penetrate deep into the ground. This is also to receive maximum water supply, by growing to the water reservoirs beneath the soil and taking in water from there. However, some xerophytes may also have underdeveloped roots, due to the limited water supply of their habitat.
Since water loss is the most pressing problem for xerophytes, their leaves have adapted in various ways to reduce the amount of transpiration occurring. The leaves of some plants like Aloe vera are vertical, so when it rains, the water will run down the leaves and into the plant, allowing for more water to be collected. Some plants such as the Alluadia procera have adapted to have extremely small leaves. This will reduce the surface area of the leaves, and reduce the amount of water being lost. Other plants however, like cacti, have no leaves at all to minimize the surface area over which water could be lost and evaporated. This will mean photosynthesis of the plant occurs in the stem.
Xerophytes also have ridges in their stem. This increases the surface area for light absorption for photosynthesis. Ridges in the stem of xerophytes also plays a part in the plant’s water balance. The ridges in the stem allow for expansion of the plant, so it can absorb the maximum amount of water. Due to the arid conditions these plants are found in, having this adaptation allows the plants to manage water balance, therefore allows them to carry out life processes efficiently, and live successfully in their way of life.
Since water loss is the most pressing problem for xerophytes, their leaves have adapted in various ways to reduce the amount of transpiration occurring. The leaves of some plants like Aloe vera are vertical, so when it rains, the water will run down the leaves and into the plant, allowing for more water to be collected. Some plants such as the Alluadia procera have adapted to have extremely small leaves. This will reduce the surface area of the leaves, and reduce the amount of water being lost. Other plants however, like cacti, have no leaves at all to minimize the surface area over which water could be lost and evaporated. This will mean photosynthesis of the plant occurs in the stem.
Xerophytes also have ridges in their stem. This increases the surface area for light absorption for photosynthesis. Ridges in the stem of xerophytes also plays a part in the plant’s water balance. The ridges in the stem allow for expansion of the plant, so it can absorb the maximum amount of water. Due to the arid conditions these plants are found in, having this adaptation allows the plants to manage water balance, therefore allows them to carry out life processes efficiently, and live successfully in their way of life.
The colour of xerophytes, such as cacti, are a relatively light green because they do not have as many chloroplasts in them as some plants of other plant groups. Many xerophytes, such as Cleistocactus strausii and Dyckia marnier-lapostollei are a silver colour. This provides an advantage, as the silver colour will reflect the sun’s rays, reducing the light intensity. As heat comes with light intensity, the temperature will be lessened, and less evaporation of water will occur, increasing the plants survival in the conditions of its environment.
Some xerophytes like Streptocarpus dimetris and edelweiss, have hair growing on them. The hairs around the stomata will trap the evaporating water, and it will condense in the hairs, creating a microclimate. This microclimate around the stomata will be high in water potential, so will reduce the concentration gradient between the inside and the outside of the plant, and result in less water being lost through transpiration.
Xerophytes plants such as Zea mays and Portulaca oleracea are known as C4 plants [3]. This means that they trap light during the day, then carry out the process of photosynthesis at night. This adaptations helps to reduce water loss in these plants, due to this affecting when they open their stomata. As they carry out photosynthesis at night, during the day when the heat and light intensity is high, the stomata can be kept closed to prevent water being lost through transpiration. Then at night, the heat and light intensity will be reduced, so the stomata will then open for gas exchange of carbon dioxide in and oxygen out. This will allow the plants to photosynthesise, and carry out their life processes to survive whilst ensuring the minimal amount of water is being lost [2].
Xerophytes plants such as Zea mays and Portulaca oleracea are known as C4 plants [3]. This means that they trap light during the day, then carry out the process of photosynthesis at night. This adaptations helps to reduce water loss in these plants, due to this affecting when they open their stomata. As they carry out photosynthesis at night, during the day when the heat and light intensity is high, the stomata can be kept closed to prevent water being lost through transpiration. Then at night, the heat and light intensity will be reduced, so the stomata will then open for gas exchange of carbon dioxide in and oxygen out. This will allow the plants to photosynthesise, and carry out their life processes to survive whilst ensuring the minimal amount of water is being lost [2].
Some plants in the xerophytes plant group, such as marram grass, have rolled leaves. This is once again an adaptation which reduces the amount of transpiration occurring. Since the leaves are rolled, enclosing the stomata inside, the air within the rolled leaf will be still, and protected from any gust of wind. This will ensure that water will not be lost so easily and blown away, and that when water is evaporated, it is kept close to the outside of the stomata. This results in the concentration gradient between the inside and the outside of the leaf being reduced, and consequentially will slow down the rate at which water is being lost through the process of transpiration.
Many xerophytes have a thick, leathery cuticle, such as the aloe plant. Having a thick cuticle helps to reduce the evaporation of water through the leaves. Since water availability is a major limitation for xerophytes, having a thick cuticle will help to ensure that water loss is reduced. Having this adaptation will help the water balance of the plant considerably.