We are a part of a diverse nature. Diversity can be seen everywhere and maybe that’s what makes our world more beautiful. We must have seen happily growing plants in a wetland even when a part of the shoot is submerged. On the other hand, we have come across some plants that cannot grow more than a few days in a waterlogged condition.
Basically different physiological adaptations found in wetland plants. The stress these plants were facing pushed them to make certain changes so that they can easily live in such conditions. Waterlogging leads to anoxic (less oxygen) later hypoxic (severely less oxygen) conditions by occupying pores of soil as well as blocking diffusion of oxygen to the depth of the soil layer. Some of the important adaptations of wetland plants are:
- Many wetland plants like water lily trap inner ethylene. Hypoxic condition enhances the synthesis of ethylene in the plant. Ethylene is a gaseous plant hormone that plays an important role in cell elongation. So petiole of water lily can grow faster towards the upper surface of the water to easily use gaseous oxygen from the atmosphere.
- Another important adaptation found in wetland plants is aerenchyma. Aerenchyma is one type of special cavities in root cortex which is filled with gas. Aerenchyma can be seen in leaves, stems also. It helps in the gaseous exchange between many parts of the plant, like shoot and root, leaf and root etc. Ethylene plays an important part in the formation of these voids. One type of programmed cell death is responsible for it which is mediated by ethylene. The dead cells in cortex then filled by gases so as to make a passage for oxygen transfer.
- Adaptation also observed in the case of metabolic processes. Gene expression profile of wetland plants is different from a normal plant. After glycolysis, genes for those enzymes involved in lactic acid fermentation and alcohol fermentation are found to be expressed during anoxia and hypoxia. Glycolysis and TCA (Tricarboxylic Acid) cycle are two important pathway of plant survival. But in the episodes of anoxia, these plants metabolically become weak and thus products of glycolysis don’t go for TCA cycle. Rather, enzyme alcohol dehydrogenase activates and ethanolic fermentation takes place.
There are certain plants found which cannot withstand for long in a waterlogged condition.
These are known as flooding sensitive plants. Garden pea and maize are examples of such plants. Usually, the adaptations of wetland plants are not found in them. The desert plant cactus can even die of overwatering. Too much care is bad for a cactus.
What actually causes it? Does water is not important for the survival of the plant?
Yes, it is. But we should not forget cactus as a desert plant. It is generally found in the arid condition where water is very less. We know that soil has pores that are filled with oxygen. When soil is well structured and pores are empty diffusion of oxygen occurs in soil layers. These are the preconditions of a cactus in its natural habitat. When cactus is planted in a garden or small pots excessive watering will cause the anoxic condition in the soil. Excessive water will occupy the micropores in soil and block diffusion of oxygen. Therefore the new condition may cause harm to the cactus plant.
So, the availability of water in the soil differently shows its effect on different plant. Some are well adapted whereas others cannot even tolerate for more than a few days. The diversity in plants cannot be studied under a single aspect. Many factors have been unfolded whereas more study is needed to understand plant behaviour properly.
by- Lukapriya Dutta, M.Sc. Botany, Gauhati University
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