Plant Adaptations
Many plant species are highly adaptable to extreme conditions, but not all.
Plants that come from places where the environment can be extremely variable are more likely to have developed biological mechanisms to withstand extremes.
Certain plants would never survive in a desert as they have not adapted to the hot and dry climate. Although some species develop well in extreme conditions and have adapted to certain climates such as the alpine zones of the snowy mountains or the hot, dry desert. Alpine species are low to the ground to withstand high winds and have minute leaves to withstand frost.
Functional Adaptations
Plants have evolved to cope with extreme environments by using both physical and chemical adaptations. Some of these are outlined below:
Water-limited Environments
Geographic areas where water is limited and infrequent are extremely stressful to plants living within these communities. Different plants have adopted a variety of techniques to deal with these conditions.
- Morphological Adaptations - certain desert plants have adapted to infrequent rainfalls by increasing their ability to store water. Plants such as Cacti have the ability to store water in their stems, leaves and trunks. These are referred to as “succulent” plants. They also keep their stomata closed during the day and open at night to reduce water loss. Bromeliads and other epiphytic (tree-dwelling) plants also have adapted to limited water availability by collecting water in a well-like structure for future use.
- Leaf Adaptations - other plants adapt to dry conditions by reducing the surface area of the leaves. They can have short, leathery leaves or spiky leaves that are rolled inwards. These assist in reducing the rate of evaporation from the plant.
- Root Adaptations - trees in arid environments, such as the Mallee of Australia have adapted their root structure to suit their environment. By adopting chemical and physical changes, they are able to enhance their water-storing ability following heavy rains. This improves their chances of surviving long drought periods which are a natural feature of the environment.
- Reproductive Adaptations – the seeds of desert plants have evolved to survive extreme temperatures and drought periods by developing hard coats to protect the embryo. They can remain dormant under the ground or exposed to the air for long periods of time prior to germination. Others have developed hooks on the outer coat to assist with dispersal by attaching to passing animal fur or skin. There are also some that will only germinate following an environmental trigger such as the external temperature dropping to a specific level, or exposure to extreme heat from fire.
Light-limited Environments
Closed forests such as rainforests have dense canopies and therefore the amount of light which reaches the forest floor is greatly limited. Many plants have adapted to these environments in different ways such as:
- Climbing plants – vines and lianas can climb higher to reach light.
- Epiphytes – live in the canopy trees where there is greater access to light.
- Darker foliage – plants that are unable to climb higher to access light may have darker foliage to help them capture and absorb more light.
- Size-restriction – some plants are able to stall their growth and remain at a small size for significant lengths of time until a light gap becomes available.
Water-inundated Environments
Trees such as Mangroves have to cope with intermittent inundation of salt water and soil which is soft and low in oxygen. These are extreme environmental stressors and mangrove plants have developed various methods to adapt to this environment such as:
- Leaf adaptations – some mangrove plants have glands on their leaves to excrete salt, others can store this salt in large amounts in their leaves. Mangroves can also move their leaves so as to reduce the size of the surface area exposed to the sun. This then reduces the amount of water lost.
- Root Adaptations – exposed roots rising vertically from the ground. These not only provide structural support for the tree but also allow for oxygen transfer to roots trapped below the ground. These roots can also halt the movement of salt to other parts of the plant.
- Reproductive Adaptations – some mangrove trees produce floating seeds that can be dispersed on the tide to avoid overcrowding. Others are viviparous (the offspring develops while attached to the adult plant). Once the offspring has matured it drops into the water, where it will stay dormant until it reaches soil.
