Geographical Distribution and Plant Communities

Few places on the Earth can be found where at least some of the 400,000 species of plants are not adapted to live. Only the polar zones, the highest mountains, the deepest oceans, and the driest deserts are devoid of plants (other than bacteria). A given plant species has a limited distribution, however, depending on its own particular requirements. Some species are broadly distributed, being tolerant of a wide range of conditions. Narrowly restricted species have limited tolerance to a specific factor, such as soil type.

Climate is the major factor affecting the distribution of plants and determining their structural adaptions. The greatest number of species are found near the equatorial regions in the tropical climates, where moisture and temperature are seldom limiting. The number of species per area decreases toward the poles.

Plants assume various adaptations as they occupy drier or colder areas away from the tropics. In drier climates plants develop features, known as xeromorphic ("dry form") characteristics, such as smaller, thicker leaves, spines, dense hairiness, and water-storage organs. In colder zones plants become lower in stature, with the growing points protected at or just beneath the ground. Because of similar adaptations, plants of a given climatic zone form a characteristic vegetation type. A large area occupying a given climatic zone and with a characteristic vegetation and associated groups of animal species is called BIOME. The major biomes include the tropical rain forest, desert, and tundra.

Current Plant Research

Much of the emphasis in research is on the development and use of new techniques and equipment. In the field of classification especially, the use of new chemical methods and computers has become important in elucidating relationships and in handling data. The electron microscope, and in recent years the scanning electron microscope (SEM), are important tools of the plant at the subcellular level. The SEM is used in particular in studying the detail of leaf surfaces and pollen grains.

Studies of the structure and function of membranes, where much of the plant's activities take place, are widely pursued. Recent research in molecular botany has been in the synthesis of chlorophyll and the interrelationships of nucleic acids and hormonal functions. The role of hormones and their interactions with phytochromes in affecting flowering continues to be an intensively studied area in plant physiology. Nearly all photosynthetic plants utilize the carbon from carbon dioxide to manufacture sugar molecules by employing one specific set of chemical reactions to fix, or transfer, the carbon atoms. The series of chemical reactions is called the 

C₃ (or Calvin-Benson) cycle because the three-carbon compound, phosphoglyceric acid, is formed during its operation. An area of recent interest has been the discovery of an alternative carbon-fixing pathway in a number of other plants.

This is called the C₄  (or Hatch-Slack) cycle because four-carbon compounds are produced during this process.

In agriculture, the main emphasis is still on increased food production, with breeding programs to develop high-yield strains, especially those yielding more protein. Computers are also used to simulate the growth of several food crops and study the factors involved.

Greenhouse Effect

In environmental science, the greenhouse effect is a popular term for the role that the variable atmospheric constituents carbon dioxide, water vapor, and trace-gases play in keeping the Earth's surface warmer than it would be without their presence. The atmosphere, when clear, is nearly transparent to the primarily shorwave radiation from the Sun, most of which is absorbed at the Earth's surface. The Earth, being much cooler than the Sun, reemits radiation most strongly at shorwave (infrared) wavelengths. The atmosphere's carbon dioxide, water vapor, and trace-gases then absorb much of this radiation and reemit a large proportion of it back toward the Earth. The term greenhouse effect implies that a comparable effect keeps the interior of a greenhouse warm. Actually, the main role of the glass in a greenhouse, besides that of admitting solar radiation, is to prevent convection currents from mixing cooler air outside with the warm air inside.


Although H₂O is an important atmospheric constituent contributing to the greenhouse effect, it is a major reason why humid regions experience less cooling at night than do dry regions, variations in CO₂ in particular, have played an important role in climatic changes. For this reason, many environment sciences have expressed concern over the global increase in amounts of atmospheric        
CO₂ in recents decades, largely as a result of the burning of fossil fuels. If the many other determinants of the Earth's present global climate remain more or less constant, the CO₂ increase should raise the average temperature at the Earth's surface. Because warm air can contain more H₂O before reaching saturation than can cooler air, the amount of H₂O would probably also increase as the atmosphere warmed. Conceivably, such a process could go on indefinitely. Some natural checks might develop. For example, negative feedbacks such as increased cloud cover and increased sea absorption of CO₂ could lower temperatures. Even a limited rise in average surface temperature, however, might lead to a significant rise in sea level and result in other environmental disruptions.
A great deal remains unknown about the cycling of carbon through the environment, and particulary about the role of oceans in this carbon cycle. Further uncertainty occurs in greenhouse effect studies because the historical temperature records being used tend to represent warmer urban areas rather than the environment as a whole. In addition, the effects of trace gases such as methane are only beginning to be understood. Despite such problems, a number of scientists maintain that the rise in global temperatures in the 1980_s is indeed a result of the greenhouse effect. 

A report issued in 1988 by three major international organizations called for furher research into the greenhouse effect and at the same time urged immediate governmental action to counteract the apparent global warming trend. By the end of the 1980_s no government had yet adopted any of the radical measures proposed by the report.                   
          

Compost

Compost is the result of a process of organic materials with the help of bacteria. Compost is not only the elements of N, P, K is so different from synthetic fertilizers. Compost contains many micro-nutrients Fe, S, Ca, Ng. This element is not present in artificial fertilizers in general. The main function of the compost is to improve the structure and improve soil quality. 

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This is steps to make compost :
- collect organic waste (waste from kitchens, gardens, livestock and Septi tanks).
- choose organic and inorganic materials.
- cut into small pieces for large material.
- mixing wet and dry organic materials.
- put it in the boxes or packed in the stack height up to 1 metre before 
  this material included should preferably cover the lower part with 
  branch, so that the air circulation more smoothly and avoid water 
  stagnation.
- control the temperature of the water content, scent, dampness and 
   acidity.
- remove from the box, while temperatures below 45 degrees Celsius, 
  when using the stack must be changed every two weeks.
- put into another box to maturation over the past two weeks.
- filtering first, before use it, so the rough can be used again, hole sieve 
   between 5-25 mm.
- It has been able to use compost.

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