Cactus – the story of water and spines

How does the cactus survive?

Cactus – Most cactuses live in deserts and semi-deserts, where the amount of water is very limited.

Some germinate and bring a flower, fruit and seed for a very brief period while there is water in the ground.

Other cast leaves after rain and live while there is water in the ground and then discard the leaves and rest until the next rain.

Cactus saves and keeps water in the body so it can be active during almost the entire year.

Interestingly, when the cactus is filled with water, it takes 90-94% of the body weight.

It has been calculated that the water content at cactus that was watered before two months is higher than in a tomato that was watered a day ago.

Another interesting thing about the cactuses is the speed at which they adopt water.

It is considered that they can fill their reserves of  water (20 liters) in couple of days since the rain fell.

But can spend that same reserve of water for 40 days.


Specific cactus metabolism

Cactuses have a special way of producing food.

This is called CAM (Crassulacean Acid Metabolism).

To produce food plants need light and carbon dioxide from the air.

Carbon dioxide enters the plant through small openings on leaves – pores.

The problem is that through opened pores water evaporates from the plants.

Cactuses have developed a special strategy thanks to CAM metabolism.

During daytime, when there is enough brightness which is necessary for producing food, cactuses close the pores and water cannot escape.

But when night falls cactuses open pores, as the night temperature is lower, so less water goes through out through the pores. During night, carbon dioxide enters the plant through open pores.

Since there is no light during night time, carbon dioxide is stored as an acid.

The next day, when the sun comes close to the pores, food production can occur because there are reserves of carbon dioxide from the previous night.

This diet allows cactus to survive long periods without rain, but this metabolism has a price – a slower growth.

For egzample, Carnegie gigantea reaches its full size after it’s 40th birthday.

What do they use spines for?

We all probably felt what it is like when cactuses try to defend themselves.

They have spines to defend themselves from being eaten or trampled. There are of course exceptions.

Great turtle from the Galapagos feeds exclusively on Prickly Pear Cactus. Some birds nest on large cactuses.

Asides for protection, spines allow propagation of cactuses.

Since spines are located also onthe fruits of cactuses, these are easy to attach to an animal passing by.

This way fruit with seeds will be transferred to some other place and allow cactus to settle in a new habitat.

Recent studies indicate that the spines also protect plant from overheating.

It is believed that wax together with spines, which covers the entire cactus body, refuses sunlight and lowers the body temperature.

Cactuses can survive temperatures over 50 degrees without consequences, while for most plants 45 degree temperatures brings serious damage. Reverse process happens at night.

As the air cools faster than the soil, spines catch long waves from the ground, and heat the plant.

Cactuses who inhabit the high terrain, where it is much colder, usually protect the most sensitive body part – the top, with dense spines and hairs.




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