Chapter 37: Plant Nutrition - A Nutritional Network

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Chapter 37: Plant Nutrition - A Nutritional Network Every organism continually exchanges energy and materials with its environment For a typical plant, water and minerals come from the soil, while

1 Chapter 37: Plant Nutrition - A Nutritional Network Every organism continually exchanges energy and materials with its environment For a typical plant, water and minerals come from the soil, while carbon dioxide comes from the air The root and shoot systems of a vascular plant ensure extensive networking with both reservoirs of inorganic nutrients Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

2 Plants require certain chemical elements to complete their life cycle CO 2 H 2 O O 2 Plants derive most of their organic mass from the CO 2 of air, but they also depend on soil nutrients such as water and minerals Minerals O 2 CO 2 H 2 O

Macronutrients and Micronutrients More than 50 chemical elements have been identified among the inorganic substances in plants, but not all of these are essential to plants A

3 Macronutrients and Micronutrients More than 50 chemical elements have been identified among the inorganic substances in plants, but not all of these are essential to plants A chemical element is considered essential if it is required for a plant to complete its entire life cycle Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

4 Researchers use hydroponic culture to determine which chemical elements are essential Control: Solution containing all minerals Experimental: Solution without potassium

5 Macronutrients and Micronutrients Nine of the essential elements are called macronutrients because plants require them in relatively large amounts The remaining eight are called micronutrients because plants need them in very small amounts Symptoms of mineral deficiency depend on the nutrient s function and mobility within the plant *Deficiency of a mobile nutrient usually affects older organs more than young ones *Deficiency of a less mobile nutrient usually affects younger organs more than older ones The most common deficiencies are those of nitrogen, potassium, and phosphorus Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

6 Symptoms of Mineral Deficiency Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient

7 Nitrogen is often the mineral that has the greatest effect on plant growth Plants require nitrogen as a component of proteins, nucleic acids, chlorophyll, and other important organic molecules Nitrogen-fixing bacteria convert atmospheric N 2 to nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

8 Soil quality is a major determinant of plant distribution and growth Along with climate, soil texture and composition are major factors determining whether a plant can grow well in a certain location Texture is the soil s general structure Composition is the soil s organic and inorganic chemical components Topsoil is a mixture of particles of rock, living organisms, and humus (the remains of partially decayed organic material) The topsoil and other distinct soil layers, or horizons, are often visible in vertical profile where there is a road cut or deep hole Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

9 Visualization of different soil horizons A B C

Water and mineral uptake by roots After a heavy rainfall, water drains from the larger spaces of soil, but smaller spaces retain water because of its attraction to clay and other particles The film

11 Water and mineral uptake by roots After a heavy rainfall, water drains from the larger spaces of soil, but smaller spaces retain water because of its attraction to clay and other particles The film of loosely bound water is usually available to plants Acids derived from roots contribute to a plant s uptake of minerals when H + displaces mineral cations from clay particles Soil particle surrounded by film of water Root hair Soil particle Water available to plant Root hair Air space Soil water Cation exchange in soil

12 Soil Conservation and Sustainable Agriculture In contrast with natural ecosystems, agriculture depletes the mineral content of soil, taxes water reserves, and encourages erosion The goal of soil conservation strategies is to minimize this damage Commercial fertilizers contain minerals that are mined or prepared by industrial processes Organic fertilizers are composed of manure, fishmeal, or compost Agricultural researchers are developing ways to maintain crop yields while reducing fertilizer use Genetically engineered smart plants inform the grower when a nutrient deficiency is imminent Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

13 Smart plants show when a nutrient deficiency is imminent No phosphorus deficiency Beginning phosphorus deficiency Well-developed phosphorus deficiency

14 Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings Irrigation and Erosion Irrigation (crop watering) is a huge drain on water resources when used for farming in arid regions It can change the chemical makeup of soil The goal of soil management is sustainable agriculture, a commitment embracing a variety of farming methods that are conservation-minded Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the United States Precautions, such as contour tillage, can prevent loss of topsoil Some areas are unfit for agriculture because of contamination of soil or groundwater with toxic pollutants Phytoremediation is a biological, nondestructive technology that reclaims contaminated areas soil reclamation

Contour tillage can prevent loss of topsoil Copyright

16 Improving the Protein Yield of Crops Agriculture research in plant breeding has resulted in new varieties of maize, wheat, and rice that are enriched in protein Such research addresses the most widespread form of human malnutrition: protein deficiency Use of such genetically modified organisms (GMOs) is on the rise and has gained press lately Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

17 Plant nutritional adaptations often involve relationships with other organisms Two types of relationships plants have with other organisms are mutualistic: Symbiotic nitrogen fixation, involving roots and bacteria Mycorrhizae, involving roots and fungi Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

18 Symbiotic nitrogen fixation, involving roots and bacteria Symbiotic relationships with nitrogen-fixing bacteria provide some plant species with a built-in source of fixed nitrogen For agriculture, the key symbioses between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants Along a legume s roots are swellings called nodules, composed of plant cells infected by nitrogen-fixing Rhizobium bacteria Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen Each legume species is associated with a particular strain of Rhizobium The development of a nitrogen-fixing root nodule depends on chemical dialogue between Rhizobium bacteria and root cells of their specific plant hosts Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

19 Symbiotic nitrogen fixation, involving roots and bacteria 5 µm Bacteroids within vesicle Nodules Roots Pea plant root. Bacteroids in a soybean root nodule.

20 Symbiotic nitrogen fixation, involving roots and bacteria Infection thread Infected root hair Rhizobium bacteria Dividing cells in root cortex Bacteroid Dividing cells in pericycle Developing root nodule Bacteroid Bacteroid Nodule vascular tissue

21 Symbiotic Nitrogen Fixation and Agriculture Crop rotation takes advantage of the agricultural benefits of symbiotic nitrogen fixation A non-legume such as maize is planted one year, and the next year a legume is planted to restore the concentration of nitrogen in the soil Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

22 Two types of Mycorrhizae and Plant Nutrition Mycorrhizae are mutualistic associations of fungi and roots The fungus benefits from a steady supply of sugar from the host plant The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption Mycorrhizae type 1: ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root cells Mycorrhizae type 2: endomycorrhizae, microscopic fungal hyphae extend into the root cells Farmers and foresters often inoculate seeds with fungal spores to promote formation of mycorrhizae Copyright 2005 Pearson Education, Inc. publishing as Benjamin Cummings

23 Ectomycorrhizae the fungi form a sheath around the plant root Epidermis Cortex Mantle (fungal sheath) 100 µm Endodermis Mantle (fungal sheath) Ectomycorrhizae. Fungal hyphae between cortical cells (colorized SEM)

24 Endomycorrhizae - fungal hyphae extend into the root cells Epidermis Cortex Cortical cells 10 µm Endodermis Fungal hyphae Root hair Vesicle Casparian strip Arbuscules Endomycorrhizae. (LM, stained specimen)

25 Epiphytes: Some plants have nutritional adaptations that use other organisms in nonmutualistic ways Staghorn fern, and epiphyte. This tropical fern (genus Platycerium) grows on large rocks, cliffs, and trees. It has two types of fronds: branched fronds resembling antlers and circular fronds that form a collar around the base of the fern.

26 Parasitic plants: Some plants have nutritional adaptations that use other organisms in nonmutualistic ways Host s phloem Dodder Haustoria Mistletoe, a photosynthetic parasite. Dodder, a nonphotosynthetic parasite. Indian pipe, a nonphotosynthetic parasite.

27 Carnivorous plants: Some plants have nutritional adaptations that use other organisms in nonmutualistic ways Venus flytrap. Pitcher plants. Sundews.

Soil and Plant Nutrition

Chapter 37 Soil and Plant Nutrition PowerPoint Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan