Roots and Soils_CH 5 Lecture Outline PDF

Chapter 5 Lecture Outline Roots and Soils Copyright © McGraw-Hill Education. Permission required for reprod...

Chapter 5 Lecture Outline Roots and Soils Copyright © McGraw-Hill Education. Permission required for reproduction or display. ©McGraw-Hill Education.  Outline Function of Roots Root Development Root Structure Specialized Roots Mycorrhizae Root Nodules Human Relevance of Roots Soils ©McGraw-Hill Education.  Function of Roots Anchor plants into soil Absorption of water and minerals Store food or water Other specialized functions ©McGraw-Hill Education.  Root Development 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 Education.  Root Development (2) 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 Fibrous root system (monocots) and some dicots ©McGraw-Hill Education.  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 Longitudinal section as lubricant through root tip – Functions in gravitropism (gravity perception) ©McGraw-Hill Education.  Root Structure (2) 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 ©McGraw-Hill Education.  Root Structure (3) Region of Elongation - Cells become several times their original length. Vacuoles merge Region of Maturation - Cells differentiate into various distinctive – Epidermalcell celltypes. extensions with thin cuticle Root hairs form. – Absorb water and minerals – Adhere tightly to soil particles Root hair zone of radish seedling – Increase total absorptive surface of root ©McGraw-Hill Education.  Root Structure Region of Maturation Cortex - Parenchyma cells between epidermis and vascular cylinder Mostly stores food Cross section of dicot root ©McGraw-Hill Education.  Root Structure Region of Maturation (2) 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. Enlargement of vascular cylinder of dicot root ©McGraw-Hill Education.  Root Structure Region of Maturation (3) Vascular cylinder - Core of tissues inside endodermis Pericycle - Outer boundary of vascular cylinder Region of– Continues to divide, even after endodermis mature and pericycle in dicot root – Forms lateral (branch) roots and part of the vascular cambium Lateral root formation ©McGraw-Hill Education.  Root Structure Region of Maturation (4) 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 ©McGraw-Hill Education.  Root Structure (3) 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 Education.  Specialized Roots  Propagative Roots Adventitious buds on roots - Develop into suckers (aerial stems) – Fruit Trees Food Storage Rootsother carbohydrates Starch and Sweet Potatoes Water Storage Roots Pumpkin family, especially in arid regions Manroot, water storage root ©McGraw-Hill Education.  Specialized Roots (2) 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 Education.  Specialized Roots (3) Aerial Roots Orchids - Velamen roots, with 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 Education.  Specialized Roots (4)  Parasitic Roots Most have no chlorophyll and dependent on chlorophyll-bearing plants for nutrition Contractile Roots Pull plant deeper into the soil Lilly bulbs, dandelions Buttress Roots Stability in shallow soil Buttress roots of Tropical Trees tropical fig tree ©McGraw-Hill Education.  Mycorrhizae 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 Education.  Mycorrhizae (2) ©McGraw-Hill Education.  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) Root nodules on roots ©McGraw-Hill Education.  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 Education.  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 Education.  Soils (2) 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 ©McGraw-Hill Education.  Soils 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 Education.  Soils 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 Education.  Soils 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 Education.  Soils 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 Education.  Soils 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 Education.  Soils (3) 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. 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 Education.  Soils 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 Education.  Soils Water in the Soil (2) 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 Education.  Soils 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 Education.  Review Function of Roots Root Development Root Structure Specialized Roots Mycorrhizae Root Nodules Human Relevance of Roots Soils ©McGraw-Hill Education. ©McGraw-Hill Education.