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Jai Ganesh

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Registered: 2005-06-28

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Xerophyte

Xerophyte

Gist

Xerophytes are a group of plants that are adapted to survive in arid regions like desert and snow-covered areas. Xerophytes have stomata with microscopic openings and elongated leaves that store large amounts of water. Sometimes even their stems store water. They have deep-spreading roots that search for water.

Summary

A xerophyte is any plant adapted to life in a dry or physiologically dry habitat (salt marsh, saline soil, or acid bog) by means of mechanisms to prevent water loss or to store available water. Succulents (plants that store water) such as cacti and agaves have thick, fleshy stems or leaves. Other xerophytic adaptations include waxy leaf coatings, the ability to drop leaves during dry periods, the ability to reposition or fold leaves to reduce sunlight absorption, and the development of a dense, hairy leaf covering.

Details

A xerophyte is a species of plant that has adaptations to survive in an environment with little liquid water. Examples of xerophytes include cacti, pineapple and some gymnosperm plants. The morphology and physiology of xerophytes are adapted to conserve water during dry periods. Some species called resurrection plants can survive long periods of extreme dryness or desiccation of their tissues, during which their metabolic activity may effectively shut down. Plants with such morphological and physiological adaptations are said to be xeromorphic. Xerophytes such as cacti are capable of withstanding extended periods of dry conditions as they have deep-spreading roots and capacity to store water. Their waxy, thorny leaves prevent loss of moisture.

Introduction

Plants absorb water from the soil, which then evaporates from their shoots and leaves; this process is known as transpiration. If placed in a dry environment, a typical mesophytic plant would evaporate water faster than the rate of water uptake from the soil, leading to wilting and even death.

Xerophytic plants exhibit a diversity of specialized adaptations to survive in such water-limiting conditions. They may use water from their own storage, allocate water specifically to sites of new tissue growth, or lose less water to the atmosphere and so channel a greater proportion of water from the soil to photosynthesis and growth. Different plant species possess different qualities and mechanisms to manage water supply, enabling them to survive.

Cacti and other succulents are commonly found in deserts, where there is little rainfall. Other xerophytes, such as certain bromeliads, can survive through both extremely wet and extremely dry periods and can be found in seasonally-moist habitats such as tropical forests, exploiting niches where water supplies are too intermittent for mesophytic plants to survive. Likewise, chaparral plants are adapted to Mediterranean climates, which have wet winters and dry summers.

Plants that live under arctic conditions also have a need for xerophytic adaptations, since water is unavailable for uptake when the ground is frozen, such as the European resurrection plants Haberlea rhodopensis and Ramonda serbica.

In environments with very high salinity, such as mangrove swamps and semi-deserts, water uptake by plants is a challenge due to the high salt ion levels. Such environments may cause an excess of ions to accumulate in the cells, which is very damaging. Halophytes and xerophytes evolved to survive in such environments. Some xerophytes may also be considered halophytes; however, halophytes are not necessarily xerophytes. The succulent xerophyte Zygophyllum xanthoxylum, for example, has specialised protein transporters in its cells which allows storage of excess ions in their vacuoles to maintain normal cytosolic pH and ionic composition.

There are many factors which affect water availability, which is the major limiting factor of seed germination, seedling survival, and plant growth. These factors include infrequent raining, intense sunlight and very warm weather leading to faster water evaporation. An extreme environmental pH and high salt content of water also disrupt plants' water uptake.

Additional Information

A xerophyte is a plant that thrives in environments with low soil moisture availability. These plants flourish in deserts or where the rainfall is naturally low; however, some xerophytes can also exist in wet habitats. These plants have unique adaptive features to stand desiccation such as reduced transpiration, high root osmotic pressure, deep roots, short vegetative period, low vegetation, and intracellular CO2 cycle.

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