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CHAPTER 26 N UTRITION AND T RANSPORT IN P LANTS Chapter Outline 26.1 Plant Nutrition and Soil A. Early Views 1. Ancient Greeks considered plants “soil-eaters” that converted soil into plant tissue. 2. The 17 th Century Dutchman Jean-Baptiste Van Helmont conducted an experiment. a. He planted a five pound young willow tree in a pot with 200 pounds of soil. b. After five years of watering, the tree weighed 170 pounds but only a few ounces of soil was missing. c. He concluded the increase in tree weight came from water; he was unaware of substances in air. B. Essential Inorganic Nutrients 1. Essential inorganic nutrients (e.g., carbon, hydrogen, oxygen) comprise 96% of plant dry weight. a. Carbon dioxide is the source of carbon for a plant. b. Water is the source of hydrogen. c. Oxygen can come from either atmospheric oxygen, carbon dioxide, or water. 2. Essential nutrient s must fulfill the following criteria. a. They have an identifiable nutritional role. b. No other element can substitute and fulfill the same role. c. A deficiency of the element causes the plant to die. 3. These elements are divided into macronutrients and micronutrients by concentration in plant tissue. 4. Beneficial nutrients are elements required for or improving growth of a particular plant. a. Horsetails require silicon as a mineral nutrient. b. Sugar beets show better growth in the presence of sodium. c. Soybeans use nickel when root nodules are present. C. Determination of Essential Nutrients 1. When a plant is burned, most mineral elements (except for nitrogen) remain in the ash. 2. Hydroponics is the preferred method for determining plant mineral requirements. a. Hydroponics is cultivation of plants in water. b. Nutrient requirements of plants are determined by omitting a mineral and observing the effects. c. If plant growth suffers, it can be concluded that the omitted mineral is a required nutrient. d. This works for macronutrients but impurities make micronutrient measurement difficult. D. Soil Formation 1. Soil formation begins with weathering of rock by freezing, glacier flow, stream flow, and chemicals. 2. Lichens and mosses grow on barren rock and trap particles and leave decaying tissues. 3. Decayed organic matter (humus) takes time to accumulate; its acidity leaches minerals from rocks. 4. Depending on parent material and weathering, a centimeter of soil may develop within 15 years. E. The Nutritional Function of Soil 1. Soil consists of soil particles, decaying organic matter, living organisms, air and water. 2. The best soil includes particles of different sizes; this provides critical air spaces. 3. Soil Particles a. Particles vary by size. 1) Sand particles are larger: 0.05–2.0 mm in diameter. 2)
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This note was uploaded on 10/24/2009 for the course BIO 172 taught by Professor Clark during the Fall '08 term at University of Michigan.

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