Plants In Extreme Conditions Essay, Research Paper
In many ways, plants are far more versatile and successful to life on earth than animals and have been here for far longer. They were the first to colonise this planet and without them we would not exist, for we are totally dependent on them. Even today with all our technology they continue to amaze us with their ability to inhabit places we humans could not survive, from the frozen Antarctic to the intensity of a volcanic spring, plants utilise their environments to their own advantage and evolve to survive the harshest of landscapes.
A plant needs four basic things to survive, water, warmth, light and minerals and any place that can provide even a little of these essential needs, will be colonised by plants. The most important environmental factors to which plants must adapt themselves to are, water availability, temperature change, light, and soil conditions. For any species, each of these factors has a small or large value, and species that have adapted to extreme environments have undergone changes to adapt to their particular and often narrow ecological conditions. It?s survival of the fittest and the plants that I shall discuss first in this essay, respond to their environment so well that they can live in a part of the world that denies them almost all of their four basic needs, the Antarctic.
The immense Antarctic ice-cap holds three-quarters of the world?s freshwater, this may seem ideal as plants need water, but plants can only use water in liquid form, and the frozen surfaces of the South Pole are inaccessible to them. Light is also a hard commodity to find here as the sun, even in summer never rises high in the sky, and in the autumn it sinks until it leaves the South Pole in darkness for half the year and as for warmth, it is the coldest place on earth. Yet three hundred miles from this place were no living thing could survive for any length of time, there are plants, algae, living together with fungi on the tips of mountains, which protrude through the snow. These hardy plants are mostly in a dormant state, the severe temperatures rising only a couple of days a year just enough to enable the Lichen to enliven their body chemistry and to photosynthesise. Some Lichen is black and this enables them to retain what little of the sun?s heat they can to melt the snow around them. Some grow on rocks that are frequented by birds as their droppings provide a rich source of nutrients. This activity however happens in the warmest part of the summer and as cold winter sets in they return to their dormant sleep.
Other algae manages to survive in the snow itself, they live in between the individual flakes just below the surface and during the summer their chlorophyll is disguised with a red pigment to protect the algae from the ultra-violet rays of the sun, as they shine more strongly through the snow. As the sun shines however, it melts the snow and does give them the liquid water they need. In the winter, when the snow is below zero the algae manufacture a kind of anti-freeze which prevents their bodies from freezing and they are invisible below the surface, but when the summer arrives once more they launch themselves forward with microscopic beating hairs and move closer to the surface and the light.
At the other end of the earth, The North Pole, the situation is different. After the Ice Age, as the ice retreated, plants began to colonise the land it revealed and as they did they evolved in to different forms, better equipped to grow in their new environment. A species of willow developed that grows not vertically but horizontally, restricted to the ground, less the fierce Arctic wind should level it. It may become as long as a European relative would grow high, but it never raises more than four inches of the ground.
In the Arctic summer, the plants that live there have a moderate supply of the four requirements. The temperature is well above freezing, so there is plenty of water around and the sun is high in the sky for weeks. The one thing they are short of however is minerals, as rocks shattered by frost in the harsh winter and ground down to a unrefined sand are unsuitable to be absorbed by the plants. The richest source of nutrients to be found are the dead decomposing bodies of the animals who live here, and the largest of these animals, the musk ox provides an excellent start in life for the seeds which are blown into it?s huge dome of a skull and they thrive in the soil surrounding the corpse which is enriched with nutrients.
Plants who live on top mountains can find that they have not only to endure the freezing nightly temperatures but also the blazing daytime sun. On Mount Kenya plants have to survive these conditions daily as the weather alternates between winter and summer every twenty-four hours. One type of lobelia has risen to the challenge and developed an ingenious way of dealing with its predicament. It?s centre forms a watertight cup that holds three quarters of a gallon of liquid, which each night freezes, on the surface, the water underneath stays liquid and therefore prevents any damage to the bud which is immersed within it. The plant now faces a second hazard, the heat of the sun evaporating the liquid, which would leave the lobelia defenceless at night. However the liquid is not rainwater but a substance secreted from a special gland and it contains a slime, which hinders evaporation.
Preservation against evaporation is also of vital importance to the plants that live in deserts. In The Namib Desert in Africa, one of the harshest deserts in the world, every drop of moisture has to be stored and used to the fullest, and the plants who live in this dry unrelenting heat have come up with many unconventional ways of scrimping and saving what little they have. One of the stranger methods of storing water belongs to the quiver tree, like the others belonging to the species it grows thick succulent leaves that grow high of the ground. This itself prevents the surface of the leaves from drying out and the stumpy branches which are coated in a fine white powder, reflects the sun?s rays. The trunk and branches of the tree are filled with a soft fibre, which can hold a large mass of water but in the most severe drought the quiver tree takes a more excessive step. The leaves must have pores for gaseous exchange, which is vital to their manufacture of food, but these pores risk moisture being evaporated, so in extreme situations, the tree amputates itself. At a point just beneath the leaves, a branch will narrow so it can no longer hold the leaves; these then will fall off. The stump then seals itself and protects the water within it. The stumps never regrow their leaves but the tree?s water needs have been reduced and other leaves saved, and the tree can survive the drought with it?s meagre supply until the rains come.
In forests, occasional destruction by fire started by natural causes, usually lightning, can have devastating effects. Temperatures of over 1000oC can be reached in these wooded areas, due to the ready source of fuel and assistance from the winds. Regular burning whether it is natural or started by man to regenerate the soil can eliminate many fire sensitive plants but also encourage species, which are adapted to fire. Features of these species include the possession of thick resistant bark and an ability to regenerate quickly after the passage of fire. Certain conifers have cones that are ?serotinous?, that is they require the heat of the fire to bring about the separation of the cone scales and release the seed. Forest fires often bring about the domination of such species to the specific areas in which they occur, the eucalyptus of Australia being another example.
So plants, by various means, solve the problem of surviving in extreme conditions. Living in intense heat, with minimum water has been accommodated to, but heavy daily drenchings can just as equally cause problems. In South America, where Venezuela, Guyana and Brazil all meet, stands a group of massive rectangular, plateaux. Their flat tops rise above the clouds and their vertical rock walls are cascading with surging waterfalls. The biggest of these is Roraima, nine thousand feet tall and ten miles long, it is sometimes called, the Lost World. It arouses images of a prehistoric place and indeed the mountain contains species that can be found nowhere else on earth, but the Roraima does not house survivors from a past age but unique species, isolated on it?s summit that have evolved extraordinary abilities to enable them to exist in an environment with the worlds heaviest rainfall.
For simple plants like algae, Roraima provides an excellent habitat but for more complex ones, life on the water-drenched rocks proves more difficult. The sodden earth supplies very little in the way of nutrients, so the plants must find other ways of finding food. Bladderworts flourish here, they are water plants that are found in wetlands all over the world and they are so expert in trapping animals that they do not grow roots at all. Their traps, little translucent capsules are able to absorb water and as they do they create a partial vacuum inside. The entrance is lined with sensitive bristles and if a small water creature touches one of these it acts as a lever, collapsing the entrance of the capsule. In then rushes the water bringing with it the creature and imprisoning it within a fraction of a second. The bladderwort then releases a digestive acid and within two hours it will have dissolved and consumed it?s victim and set its trap again.
Another plant that prospers below the surface is water celery, they absorb all the oxygen and carbon dioxide they need from the water around them and it also utilises the water to pollinate. The female flower opens its petals underwater, then rapidly moves to the surface. The male flower makes its journey to the surface even more quickly and on its way breaks its stem, at the surface it unfurls its petals and using the stamens as sails, heads towards the anchored female and they collide so violently that the pollen is knocked out of its anthers. Once the female flower has reached fertilisation, it closes, and its stem tightens into a corkscrew, recoiling back under the surface and there safely under water it develops its seed.
Most of the world?s surface is covered by seawater and most of it is beyond the reach of flowering plants. The only plants that can prosper here are floating single-celled algae, the simplest of all plants. They have all of the four fundamental needs in abundance. The water never drops more than a degree or so in temperature, there is always available sunlight and they are never in short supply of nourishment as rich flow of nutrients float up from the seabed. They are the basis of all life in the sea and perhaps the least considered by humanity, tiny creatures of the sea consume them. Among these consumers are corals and crustaceans, molluscs and fish (plankton), which in turn feed the rest of the seabed. And more importantly we land animals depend on them, for they are the main factor in maintaining the balance of gases in earth?s atmosphere and they produce the majority of the oxygen we breath.
Plants have colonised almost the earth?s entire surface; in fact only about 6% of the earth has no vegetation cover. They exist in the most extreme temperatures and survive and evolve in the strangest of environments. Yet they have one adversary, man who poses a greater threat than any other living thing. In a relatively short period of time man has plundered the earth, leaving about 10% of the flowering plants close to extinction. We must begin to realise that this action threatens our fragile ecosystem that we ultimately depend on. It is time for us to cherish our green friends and instead of destroying them, start to feel privileged to co-inhabit this planet with them, for without them we will certainly perish.