Xerophytes are a group of plants that, in the process of evolutionary changes, have adapted to a lack of moisture in the environment. It is not homogeneous in terms of physiological characteristics. In some, transpiration processes are reduced, while in others, on the contrary, they are enhanced. Ways to overcome drought in xerophytes are different. P. L. Genkel developed a classification of flora that can tolerate a long absence of moisture.
Succulents
This group includes plants that have adapted to store water in tissues and organs. Bright representatives of xerophytes are cacti and crassula. Moisture accumulates in sufficient quantities in fleshy stems (spurge, cactus) and leaves (aloe, young, stonecrop, agave).
Characteristic signs of succulents:
- The surface from which moisture evaporates has been reduced.
- Leaves are reduced.
- Thick cuticle that limits transpiration.
- The root system is shallow, but abundantly overgrown.
- There is little cell sap in the roots.
Succulents are found in areas where a period of heavy rains is replaced by a long drought. To reduce water loss, stomata open only at night. Lack of water plants of this typeendure badly. They are more adapted to the heat than to the drought, during which they economically spend the fluid stored in the tissues.
Euxerophytes
Real xerophytes are plants that can significantly reduce moisture loss when it is deficient. In the process of evolution, euxerophytes received the following adaptations at the cellular level:
- Increased elasticity of the cytoplasm.
- Reduced water content.
- Increased moisture retention.
- Increased viscosity.
All this helps to absorb moisture from the almost dry soil. Sometimes the underground parts and stems of euxerophytes are overgrown with a cork layer. A thick layer of cuticular sheath covers the leaves of xerophytes. Plants of this group have stomatal protection in the form:
- The recesses in which they are located.
- Resin and wax caps.
- Curling leaves into a tube.
Representatives of euxerophytes: saxaul, sand acacia, aristida, some types of wormwood, etc.
Hemixerophytes
If you parse the meaning of the word "xerophytes", you can see that it is formed from the Latin words "dry" and "plant". Therefore, it is part of the flora adapted to moisture-deficient habitats.
What are xerophytes of this group and why are they unique? Hemixerophytes are distinguished by their developed adaptations for extracting water from great depths. Their roots go far underground and branch heavily. In underground cellsnegative water potential and highly concentrated cell sap.
These features help extract moisture from huge volumes of soil. If the aquifer is not very deep, then the root system can reach it. The abundance of branching veins on the leaves minimizes the time of moisture delivery from roots to cells.
This type of xerophyte transpiration is more intense than others. Thanks to this, the leaves are cooled and even in the heat, photosynthetic reactions take place in them. This is well manifested in the steppe alfalfa, wild watermelon, cutter and sage.
Pseudoxerophytes
False xerophytes are plants whose life is so short that they do not catch the dry season. Their growing season coincides with the rainy season. They experience adverse conditions in the stage of bulbs, seeds, tubers or rhizomes.
Poikiloxerophytes
Poikiloxerophytes are plants that are unable to regulate water metabolism. They wait out the dry period in a state of suspended animation. At this time, the metabolism does not occur or is very slow.
Ferns, some algae, most lichens and some angiosperms are poikiloxerophytes. This group is distinguished by the ability of the protoplast to thicken to a gel-like state. After that, being dry to the touch, they continue to live. With the onset of the rainy season, these plants return to their normal state. Loss of water for them is notpathology.
Xerophytes: signs and features
The anatomy of a leaf largely depends on the tier in which it is located. Dependence was called the Zalensky law, after the name of the physiologist who discovered it. With increasing height above the ground:
- The size of the cell is decreasing.
- The lumen of the stomata is decreasing.
- The density of veins and stomata increases.
- Getting more palisade parenchyma.
- Transpiration and photosynthesis intensity increase.
The reason for the discovered pattern lies in the deterioration of the supply of moisture located at the top of the leaves. A similar picture is observed in relation to plants growing in a dry climate. The xeromorphic structure is characteristic of the leaves of drought-adapted species.
The transpiration coefficient characterizes how rationally moisture is spent. The degree of openness of the stomata equally affects both evaporation and the accumulation of dry matter.
Attempts to make plants more resistant to drought are carried out by genetic engineers and breeders. Other methods are suggested:
- Presowing hardening of seeds: drying them after soaking.
- Fertilization, which helps retain moisture in the cells.
- Treatment with hormonal drugs.
- Agrotechnical practices (rolling, spring harrowing, etc.).
Scientists, when developing methods, rely on the experience of xerophytes. By studying their structure and metabolic processes, they offer ways to adaptcultivated plants to unfavorable conditions. As a result, drought-resistant varieties are emerging in agriculture.
