September 2017

Physiology is the study of the various functions performed in and by living organisms. Physiological processes of plants include the flow of energy, movement of solutes, and control by hormones. Chemical reactions are mediated (their rate is controlled) by enzymes.

For example, those studying plant physiology are concerned with the way that plants trap light energy as light is absorbed by chlorophyll. As a result of a series of chemical reactions, glucose, a six-carbon carbohydrate, is formed (preceding glucose are molecules of PGAL, a three-carbon sugar, which pair to form glucose). The glucose may be oxidized within the same cell or within another cell of the same plant (or utilized by an animal). This oxidation process produces adenosine triphosphate (ATP). As this compound is converted to adenosine diphosphate (ADP), energy is released, allowing organisms to perform other essential energy-requiring life activities.

Plant physiologist would also be concerned with the transport of nutrients and water throughout a plant. By means of their roots, plants absorb water and dissolved materials from the soil, after which they are conducted upward, by means of xylem tissue, to all parts of the plant. This upward movement is called transpiration. The glucose formed in leaves is dissolved in water and transported, by means of phloem tissue, to all parts of the plant. This movement, called translocation, is commonly downward, but also may be upward. By these processes, water, minerals, and sugars are transported to all parts of a plant.

Another area of concern for plant physiologists is the function of plant hormones (phytohormones), in fact, those specializing in this area have their own discipline, endocrinology. Phytohormones are compounds produced within a plant. They are transported to other parts of plant, where they regulate growth and development. Early in the twentieth century, auxin was the first phytohormone to be discovered. It promotes growth by causing cells to elongate but was found also to inhibit growth of lateral buds. Gibberellins, a second group of hormones, also stimulate growth by causing cell elongation. Among their activities is the promotion of seed germination. Cytokinins are abundant in dividing tissues, where they stimulate cell division. Abscisic acid is a growth inhibiting hormone that maintains dormancy in buds and fruits and also is associated with the falling of leaves in autumn. Ethylene causes fruits to ripen. Several hormones are used in agriculture for increasing growth rates of crops.

See also: Cytology, Anatomy

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The first agricultural revolution occurred in Asia and involved the domestication of plants and animals. It is believed that vegeculture first developed in Southeast Asia more than eleven thousand years ago. In vegeculture, a part of a plant other than the seed is planted for reproduction. The first plants domesticated in Southeast Asia were taro, yam, banana, and palm. Seed agriculture, now the most common type of agriculture, uses seeds for plant reproduction. It originated in the Middle East about nine thousand years ago, in the basins of the two major rivers of present day Iraq, the Tigris and the Euphrates. Wheat and barley were probably the first crops cultivated there. Although many plants were domesticated simultaneously in different parts of the world, rice, oats, millet, sugarcane, cabbage, beans, eggplant, and onions were domesticated originally in Asia.

Asia supports about 60 percent of the global population on only about 23 percent of the world’s agricultural land. As a result, Asian agriculture is far more intensive than on any other continent. Despite the population pressure on arable land, Asia has made remarkable progress in agricultural productivity. Between 1966 and 1995, wheat production grew 5.5 percent annually, and rice production 2.2 percent. In Asia as a whole, food production has outpaced the growth of population. In most Asian countries, particularly in the low income countries of South Asia, per-capita food availability has risen.

Agrarian Structure

Most people in Asia are farmers, owning an average of about 2.5 acres (1 hectare) of land per family. Topographic and climatic conditions, to a large extent, determine farm size. Agricultural potential is limited in Nepal, for example, because of the Himalaya Mountains, and in Saudi Arabia because of the Arabian Desert. In these countries, average farm size is larger relative to countries like Bangladesh.

Another feature of Asian agrarian structure is the inequitable distribution of farmland. For example, in India more than 25 percent of cultivated land is owned by less than 5 percent of farming families. Farm holdings in most Asian countries are highly fragmented, and tenancy is widespread. Fragmentation of farms inhibits agricultural mechanization, and land consolidation efforts have had limited success in most Asian countries.

Most Asian farmers are subsistence farmers, cultivating crops for family consumption. Almost all farm operations are done manually or with the help of draft animals. Exceptions are found in Japan, South Korea, and Taiwan, where small scale equipment similar to garden tractors is widely used. Only recently have Asian farmers started to use chemical fertilizer, for water, they largely depend on rain. As a result, yields are low, which compels farmers to cultivate the land intensively. Double cropping is the norm, some farmers grow three crops a year. Therefore, only a small fraction of the arable land in humid regions of Asia remains fallow. Farming is labor-intensive, and the extended family is the main source of labor. This helps to explain why family size is generally large in agrarian countries of Asia.

Rice and Wheat

The coastal areas and inland river valleys of East, Southeast, and South Asia are the agricultural cores of the continent.

Continue of the article: Rice and Wheat

Slash

In the tropical rain forests of Southeast Asia, the mountainous and hilly parts of South Asia, and in southern China, a type of primitive agriculture known as shifting cultivation or slash and burn agriculture is practiced.

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Export Crops

Plantation crops such as tea, rubber, coconuts, and coffee are grown in Asia.

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Forestry

Forests of significant economic importance are found primarily in northeastern East Asia and Southeast Asia.

Continue of the article: Forestry

See also: ASIAN FLORA

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