Roots and Soils Chapter 5 PDF

Because learning changes everything. ® Chapter 5 Roots and Soils FIFTEENTH EDITION James E. Bidlack, Shelly H. Jansky © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribu...

Because learning changes everything. ® Chapter 5 Roots and Soils FIFTEENTH EDITION James E. Bidlack, Shelly H. Jansky © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill.  Outline 1 Introduction to Roots and Soils Root Structure How Roots Develop The Root Cap The Region of Cell Division The Region of Elongation The Region of Maturation Specialized Roots Food-Storage Roots Water-Storage Roots Propagative Roots Pneumatophores Aerial Roots Contractile Roots Buttress Roots Parasitic Roots © McGraw Hill © Glowimages 2  Outline 2 Mycorrhizae Root Nodules Human Relevance of Roots Soils Parent Material Climate Living Organisms and Organic Composition Topography Soil Texture and Mineral Composition Soil Structure © McGraw Hill 3  Introduction to Roots and Soils Functions of roots: Anchor plants into soil Absorb water and minerals Store food or water Other specialized functions © McGraw Hill 4  How Roots Develop Upon germination, embryo’s radicle grows out and develops into first root. Radicle may develop into thick taproot with thinner branch roots. Dicotyledonous plants (dicots) Taproot system © McGraw Hill 5  Adventitious and Fibrous Root Development Or, after radicle formation, adventitious roots may arise that develop into a fibrous root system. Adventitious roots do not develop from another root, but instead from a stem or leaf. Fibrous roots - Large number of fine roots of similar diameter Monocotyledonous plants (monocots) and some dicots Fibrous root system © McGraw Hill 6  Root Structure 4 regions: Root cap Region of cell division Region of cell elongation Region of maturation Root Cap - Thimble-shaped mass of parenchyma cells covering each root tip Protects tissues from damage as root grows Secretes mucilage that acts as lubricant Longitudinal section through root tip Functions in perception of gravity Access the text alternative for slide images. © McGraw Hill 7  Region of Cell Division Composed of apical meristem in the center of root tip Subdivided into 3 meristematic areas: Protoderm - Gives rise to epidermis Ground meristem - Gives rise to cortex and pith Procambium - Gives rise to primary xylem and primary phloem Root tip showing primary meristems Access the text alternative for slide images. © McGraw Hill 8  The Region of Elongation Region of Elongation - Cells become several times their original length. Vacuoles merge Root cap and apical meristem are pushing through the soil. No further increase in cell size takes place above the region of elongation. Remainder of root usually stays stationary for the life of the plant Increases in girth may occur if cambium is present © McGraw Hill 9  Region of Maturation Region of Maturation - Cells differentiate into various distinctive cell types. Root hairs form. Absorb water and minerals Tubular extensions of specialized epidermal cells Sometimes called the region of differentiation or the root hair zone © McGraw Hill (a) © Kingsley Stern 10  The Cortex Parenchyma cells between epidermis and vascular cylinder Mostly stores food Endodermis - Inner boundary of cortex, consisting of a single-layered cylinder of compact cells Cell walls impregnated with suberin and lignin on radial and transverse walls bands called Casparian strips Forces water and dissolved substances entering and leaving the central core to pass through endodermis Regulates types of minerals absorbed Eventually inner cell walls become thickened with suberin, except for passage cells. © McGraw Hill 11  Enlargement of the Vascular Cylinder of a Dicot Root Access the text alternative for slide images. © McGraw Hill (a-b) © James E. Bidlack 12  The Vascular Cylinder Vascular cylinder - Core of tissues inside endodermis Pericycle - Outer boundary of vascular cylinder Access the text alternative for slide images. © McGraw Hill Left:© James E. Bidlack ; Right: © G. S. Ellmore 13  Cells of the Vascular Cylinder Most of cells of vascular cylinder are primary xylem or primary phloem. In dicot or conifer roots - Solid core of xylem, with “arms” in cross section Vascular cylinder of dicot root Access the text alternative for slide images. © McGraw Hill (b) © James E. Bidlack 14  Development of Cambium In most dicots and conifers: Vascular cambium develops from parts of the pericycle and other parenchyma cells between the xylem arms and phloem patches. In woody plants: Cork cambium arises in the pericycle outside of the vascular cambium © McGraw Hill 15  Growth Determinate growth - Growth that stops after an organ is fully expanded or after a plant has reached a certain size Indeterminate growth - New tissues are added indefinitely, season after season © McGraw Hill 16  Specialized Roots Most plants produce a fibrous root system, a taproot system, or a combination of the two. Some plants have roots that are modified for functions beyond mineral and water absorption. © McGraw Hill 17  Food-Storage Roots Most roots and stems store food Certain plants store large amounts of starch and other carbohydrates Sweet Potatoes and yams: Extra cambial cells develop in parts of xylem Produce large numbers of parenchyma cells Organs swell and provide storage areas for carbohydrates © McGraw Hill © KPG_Payless/Shutterstock 18  Water-Storage Roots Some members of the Pumpkin family, especially in arid regions, produce huge water-storage roots Manroot, water storage root © McGraw Hill Courtesy of Paul Furman 19  Propagative Roots Adventitious buds on roots develop into suckers (aerial stems) Common in Fruit Trees © McGraw Hill 20  Pneumatophores In plants with roots growing in water Spongy roots that extend above the water’s surface and enhance gas exchange between atmosphere and subsurface roots Mangrove pneumatophores © McGraw Hill (a) Majority World/Getty Images; (b) © Majority World/ Contributor/Getty Images 21  Aerial Roots Orchids Velamen roots epidermis several layers thick to reduce water loss Corn Prop roots support plants in high wind Ivies (English ivy, Virginia creeper) Aerial roots aid plants in climbing Orchid aerial (velamen) roots © McGraw Hill © Kingsley Stern 22  Contractile Roots Seen in some herbaceous dicots and monocots Pull the plant deeper into the soil Lily bulbs are pulled deeper into the soil each year Access the text alternative for slide images. © McGraw Hill 23  Buttress Roots Some tropical trees growing in shallow soil produce bug roots Stabilizes tree Buttress roots of tropical fig tree © McGraw Hill © Kingsley Stern 24  Parasitic Roots Produced by plats that include dodders, broomrapes, and pinedrops Most have no chlorophyll and dependent on chlorophyll- bearing plants for nutrition Haustoria are peglike extensions that allow them to parasitize a host © McGraw Hill 25  Terminology Saprophyte: fungi, obtain nutrients from organic matter Epiphytes: grow on other plants but obtain nutrients and moisture from the environment Orchids Epiparasite and myco-heterotroph are sometimes used to describe plants that obtain some or all of their carbon from a fungus rather than from photosynthesis Indian pipe © McGraw Hill 26  Mycorrhizae Fungi that form a mutualistic association with plant roots Mutualistic association: Both fungus and root benefit and are dependent upon association for normal development Fungi facilitate absorption and concentration of nutrients, especially phosphorus for roots. Plant furnishes sugars and amino acids to fungus. Plants with mycorrhizae develop few root hairs compared with those growing without an associated fungus. Particularly susceptible to acid rain © McGraw Hill 27  Longitudinal and Cross Sections of Mycorrhizae Access the text alternative for slide images. © McGraw Hill (c-d) © Kingsley Stern 28  Root Nodules Plants cannot convert free nitrogen to usable form A few species of bacteria produce enzymes that converts nitrogen nitrates and other nitrogenous substances readily absorbed by roots. Root nodules contain large numbers of nitrogen-fixing bacteria. Legume Family (Fabaceae) © McGraw Hill © Kingsley Stern 29  Human Relevance of Roots Sources of food Carrots, sugar beets, turnips, horseradishes, cassava (tapioca), yams, sweet potatoes Spices Sassafras, sarsaparilla, licorice Dyes Drugs Aconite, ipecac, gentian, reserpine Insecticide Rotenone © McGraw Hill © Shelley H. Jansky 30  Soils Soil is formed through the interaction of climate, parent material, topography, vegetation, living organisms and time. Solid portion of soil consists of minerals and organic matter. Pore spaces between solid particles filled with air or water. © McGraw Hill 31  Soil Horizons Soils divided into horizons: Topsoil (10-20cm) A horizon - Dark, with more organic material than lower layers E horizon - Light B Horizon (0.3-0.9m) - Subsoil More clay, lighter in color than topsoil C Horizon (varies) - Parent material which extends to bedrock Access the text alternative for slide images. © McGraw Hill Provided by Steven McGowen, USDA-NRCS 32  Parent Material Parent material - Rock that has not been broken down into smaller particles Rock types: Igneous – Volcanic Sedimentary - Deposited by glaciers, water or wind Metamorphic - Changes in igneous or sedimentary rocks from pressure or heat © McGraw Hill 33  Climate Climate varies throughout the globe, as does its role in weathering of rocks Deserts - Little weathering by rain, and soils poorly developed In areas of moderate rainfall - Well-developed soils Areas of high rainfall - Excessive water flow through soil leaches out important minerals. © McGraw Hill 34  Living Organisms and Organic Composition In soil there are many kinds of organisms, roots and other plant parts. Bacteria and fungi decompose organic material from dead leaves, plants and animals. Roots and other living organisms produce carbon dioxide, which combines with water and forms acid that increases the rate at which minerals dissolve. Small animals alter soil by their activities and by their wastes. Humus - Partially decomposed organic matter, gives soil a dark color © McGraw Hill 35  Topography Topography - Surface features Steep areas: Soil may erode via wind, water or ice. Flat, poorly drained areas: Pools and ponds may appear. Development of soil arrested. Ideal topography permits drainage without erosion. © McGraw Hill 36  Soil Texture and Mineral Composition Soil Texture - Relative proportion of sand, silt and clay in soil Sand - Many small particles bound together chemically Silt - Particles too small to be seen without microscope Clay - Only seen with electron microscope Individual clay particles called micelles Negatively charged and attract, exchange or retain positively charged ions, such as Mg++ and K+ © McGraw Hill 37  Agricultural Soils Best agricultural soils - loams composed of 40% silt, 40% sand and 20% clay Coarse soils drain water too quickly. Clay soils allow little water to pass. © McGraw Hill 38  Soil Structure Soil Structure - Arrangement of soil particles into aggregates Productive agricultural soils are granular with pore spaces occupying between 40-60% of the total soil volume. Particle size is more important than total volume. © McGraw Hill 39  Water in the Soil Hygroscopic Water - Physically bound to soil particles and unavailable to plants Gravitational Water - Drains out of pore spaces after a rain Capillary Water - Water held against the force of gravity in soil pores Determined by structure and organic matter, by density and type of vegetation, and by the location of underground water tables Plants mostly dependent upon this type. © McGraw Hill 40  Terminology for Water in the Soil Field capacity - Water remaining in soil after water drains away by gravity Determined by texture, structure and organic content of soil Permanent Wilting Point - Rate of water absorption insufficient for plant needs Plant permanently wilts. Available Water - Soil water between field capacity and the permanent wilting point © McGraw Hill 41  Soil pH Affects nutrient availability Alkalinity causes some minerals, such as copper, iron and manganese to become less available. Counteract by adding sulfur, which is converted to sulfuric acid by bacteria, or by adding nitrogenous fertilizers Acidity inhibits growth of nitrogen-fixing bacteria. Counteract by adding calcium or magnesium compounds = liming © McGraw Hill 42  End of Main Content Because learning changes everything. ® www.mheducation.com © 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw Hill.