The Intriguing Behaviour of Plants and Their Unique Physical Traits

Why Do Leaves Change Colour From Green to Yellow or Red Before Falling?

Come autumn, the maples change their attire to myriad shades. It is a visual treat for us, but the plant's existence hangs between death and life. Maple leaves are normally green because they have chlorophyll, which helps photosynthesis. As the leaves age, chlorophyll production is reduced.

The green colour changes when the chlorophyll is not in the required quantity to cover up other pigments, for example, carotene and xanthophyll. So, the green fades, and yellow, red or brown takes over.

It is also hypothesised that the changing colour of autumn leaves is an adaptive strategy—the bright colours could be a warning signal to parasitic insects that become active in autumn, confusing and scaring them off from attacking the tree. Harmless insects profit from this. They lay eggs on these trees without competition from parasitic insects that eat their eggs. Just as we rely on certain attire and makeup to gain new friends and avoid undesired attention, plants use their changing colours to ward off parasitic insects.

There are complex reasons behind the intriguing behaviour of plants, and understanding them can remind us of our similarities to plants in terms of survival and success.

Why Do Some Plants Have Big Leaves and Some Small?

Plants have bigger leaves to capture maximum sunlight for photosynthesis. Plants with big leaves grow under the shade of other trees. There are disadvantages to having a big surface area for a leaf, as there will be more evaporation from it. However, as the big-leaved plants usually grow in the lower strata of a forest, there won’t be much direct sunlight falling on them. Hence the evaporation will be low. These plants usually grow in places with greater water availability. They often live inside ecosystems with water abundance. Examples are banana, yam, and colocasia.

Plants with smaller leaves are usually the ones that grow in water-deficient ecologies. The reduced leaf size helps minimise evaporation. Neem, gooseberry, and tamarind belong to this category. The smaller leaves are also found to have longer major veins running through them for water flow, compared to bigger leaves. This extensive water network helps them cope with water scarcity by providing alternative water pathways, which go around the bubble blockages that form in the veins during dry spells. This demonstrates an economy of living in action.

The Intriguing Behaviour of Plants: Do Trees Communicate With Each Other?

Modern plant science says that trees communicate with other trees. When eaten by animals and insects, certain trees and plants can not only secrete toxic substances to ward them off, but also the scent of these substances gives a warning to the nearby trees. The neighbouring trees are thus prompted to secrete the same toxins.

Also, when attacked by leaf-eating insects, some trees summon up the predators of those very same insects by secreting certain pheromones, which are predator-specific and insect-specific.

This fact keeps one wondering whether the plants can see or sense each other.

The tree roots communicate with each other through the fungi network attached to all of them, by way of their root network, and this network is phenomenal. It spans entire continents if not the whole planet.

This network is what scientists call the 'Wood Wide Web'. Trees share nutrients too through it.

Experiments proved that if an area has many willow trees, caterpillars might devour some trees, but the infestation does not further spread around them.

This is because the neighbouring trees are warned somehow by the infested trees, and as a result, they produce some toxins in their leaves that ward off the caterpillars.

Do Plants Climate-Migrate?

Most plants can adapt to different climates, geographies and ecosystems.

Individual species of plants are gradually migrating north to overcome the situations created by climate change. It is a slow Exodus. This will cause the biodiversity of the southern hemisphere to shrink, whereas that of the northern hemisphere will increase. The geopolitical consequences of such a change will be beyond today’s understanding and imagination.

Why Do Some Saplings Flower Before Maturity?

Negative climate and soil circumstances prompt a plant to flower immaturely.

For example, when there is water scarcity and a resulting threat of wilting, a sapling will flower in a last-ditch effort to sustain the species. It is rather a drastic final effort of species continuation.

If the drought persists, the plant will die but mostly after leaving behind a few seeds that can grow into new plants.

All the energy and resources of the plant at this time will be redirected to the flower setting, fruit setting and ripening of the fruit. Modern agriculture manipulates this tendency to get maximum flowering from a crop. Just a few days before the flowering stage, farmers stop irrigation. Then the plants would flower more abundantly than usual. After flowering completes, irrigation is restarted. The result the farmer gets is maximum flower setting and maximum yield.

Can a Plant See?

Creepers can sense the nearby tree. They grow in the tree's direction to use it as a prop.

If we change the position of an artificial prop, the plant will also change its course.

This is an observable fact and happens in a few hours. How does the plant know the prop has changed position? Do they see, smell, or listen to their surroundings?

What exactly is happening in this simple act of a plant?

An experiment by Charles Darwin and his son Francis proved that the light-sensitive cells of a seedling are located at the tip of its shoot. So we can say, the eyes of the plants are on the tip of the shoots. As far as the purpose of the eye is to detect light, this is true. However, the plant has no central nervous system that can process this information and make a mental picture as we do. Instead, the ‘eye’ of the plant detects light and sends a signal to the plant parts that need to bend towards the light.

Plants can also detect smell. Dr Consuelo De Moraes, an entomologist, conducted an experiment in which she showed the parasitic dodder plant, which gets itself attached to another plant like a tomato and steals its nutrients from its stem, is led by the scent of the host plant.

The scientist could even trick the dodder to get attached to sticks smeared with tomato smell.

Many ways of seeing and smelling exist among animals which are different from how humans do it. Plants are not exempt from these sensory experiences, as we would have believed once.

References

Chamovitz, D. (2012), What a plant knows, London: Oneworld Publications.

Wyman, D. (1986), Wyman’s gardening encyclopedia, New York: Simon and Schuster, p.98.

Archetti, M. (2000), The origin of autumn colours by coevolution, Journal of Theoretical Biology, 205, pp. 625-630.

Wolpert, (July 5, 2011), Being small has its advantages, if you are a leaf, UCLA Newsroom.

Wohlleben, P. (2016), The hidden life of trees: What they feel, how they communicate – discoveries from a secret world, London: Penguin UK.

Maschinski, J. and Haskins, K.E., (2012), Plant reintroduction in a changing climate: Promises and perils, Washington D.C.: Island Press. P.230.