Essential elements are required by plants for normal growth and reproduction

More than 60 elements have been found in plant tissues. These elements range from those as common as carbon and hydrogen to those as exotic as platinum, uranium, and gold. Are all of these elements essential for growth? If so, what functions do they perform? Answering these questions has proven to be a formidable task. We must first define what we mean by "essential." An element is essential if (1) it is required for normal growth and reproduction, (2) no other element can replace it and correct the deficiency, and (3) it has a direct or indirect action in plant metabolism; that is, in the normal plant functioning. Thus, the mere presence of an element in a plant does not necessarily mean it is essential.

Armed with this definition, botanists began studying the 92 naturally occurring elements to determine how each might influence plant growth. Their approach was simple: an element would be deemed essential only if a plant could not grow and reproduce without it (fig. 7.27). Many of the early experiments to determine essential elements involved hydroponics, a technique for growing plants without soil in a solution of water and specific chemicals (fig. 7.28). By the middle of the 1800s, these experiments had shown that plants require at least nine elements: carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulfur, calcium, and magnesium. Because these elements are required in relatively large amounts (i.e., usually more than

Mineral Nutrition Plants Experiment

FIGURE 7.27

Discovering essential plant nutrients. Plant physiologists transplant a seedling to a solution lacking only one of the ingredients thought to be essential for growth, substance "A" in this example. If the plant grows and reproduces normally after being transplanted, the missing ingredient is assumed to be nonessential.

FIGURE 7.27

Discovering essential plant nutrients. Plant physiologists transplant a seedling to a solution lacking only one of the ingredients thought to be essential for growth, substance "A" in this example. If the plant grows and reproduces normally after being transplanted, the missing ingredient is assumed to be nonessential.

Hydroponic Farming

FIGURE 7.28

Hydroponic farming. In this apparatus, a solution of nutrients flows over the roots of lettuce growing in water.

FIGURE 7.28

Hydroponic farming. In this apparatus, a solution of nutrients flows over the roots of lettuce growing in water.

0.5% of the dry weight of the plant), they became known as macronutrients (fig. 7.29).

Subsequent studies of the mineral nutrients encountered several problems, including contamination. For example, "pure" water and chemicals used to prepare nutrient solutions often contained enough mineral impurities to

^Mjcronutrients" OJ^

"Macronutrients" 3.5%

Other

Carbon, hydrogen, and oxygen

"Macronutrients" "Micronutrients"

Nitrogen Iron

Potassium Chlorine

Calcium Manganese

Phosphorus Boron

Magnesium Zinc

Sulfur Copper

Molybdenum

FIGURE 7.29

The proportional weights of various elements in plants. Macronu-trients and micronutrients together total only 4% of the total weight of the plant, but they are essential to the plant's life and growth.

satisfy plants' requirements for several elements. Furthermore, the growth containers used in hydroponics experiments were often made of glass that contained large amounts of boron. When these containers were filled with nutrient solutions, enough boron dissolved out of the glass to satisfy the plant's requirement for boron. Such impurities, combined with insensitive methods for detecting many elements, made it impossible to determine the essentiality of many elements.

New techniques and more sensitive instruments helped botanists discover seven other essential elements: iron, chlorine, copper, manganese, zinc, molybdenum, and boron. Because these nutrients are required in relatively small amounts (i.e., usually only a few parts per million), they are called micronutrients, or trace elements. For example, the micronutrient boron is required, but as little as five parts per million are needed by some plants. This means that if you were to count all the atoms of a plant, out of every million atoms, only five of them would be boron.

Although required in smaller amounts than macronutrients, micronutrients are equally essential for growth. The 4 metric tons of carbon, hydrogen, and oxygen are no more important to an Idaho potato farmer's crop than are the 2.5 grams (less than the weight of a dime) of copper. The study of how a plant uses these essential elements is plant mineral nutrition.

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Responses

  • Kirsten
    What makes a mineral element essential for plant growth?
    4 years ago
  • MEDARDO LOGGIA
    What makes a mineral element essential for plant growth quizlet?
    4 years ago
  • Anneli
    How many essential are required for normal growth of plants?
    4 years ago
  • russom
    What are the 16 elements to be essential for growth and reproduction?
    4 years ago
  • bucca
    Why mineral nutrients need for plants?
    3 years ago
  • Asmait
    How many essential nutrients are required by plants to fulfil their growth requirement?
    3 years ago
  • aman
    How many essential nutrients are required by plants to fulfil their growth requirements?
    1 year ago
  • Negisti
    Which element are essential for a normal plant?
    1 year ago
  • emogene
    How can you determine the essentiality of mineral elements?
    11 months ago
  • marc
    How to determine ghe essentiality of an element?
    11 months ago
  • dale foster
    How essentiality of an eliment isdetermined?
    10 months ago
  • james meehan
    Which element is required in large amount by plant?
    9 months ago
  • Jessica
    What required elements to be essential?
    8 months ago
  • gerardo
    How essential of elements is determined?
    5 months ago

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