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9/15/2011 Roots Essential for Plant Growth • Root System & Soil Environment Have Great Effect on Plant Life & Productivity http://www.biologyreference.com/Re-Se/Roots.html Radicle • First Root from a Seed Is the Radicle – Develops into the Primary Root Fibrous Root System • Primary Root Does not Develop much • Fibrous Systems Are more thoroughly Distributed & Absorb more Water & Nutrients within the Root Zone than Tap Root Systems • Allows Greater Contact within Rooting Zone Taproots • If Primary Root Continues to Grow & Develop, Plant Has a Taproot System – Can Grow Deeply into Soil – Some Harvested for Food Secondary Roots • Branch from 1° Roots or Arise from Plant Stem Tissue • May Be Roots from Underground – Common in Grass Crops 1 9/15/2011 And More • Tertiary Roots – Arise from 2° Roots • Quaternary Roots – Arise from Tertiary Roots • Quinary Roots Adventitious Roots • Arise from Stem or other non-Root Meristems • May Be 2° Roots • Adventitious Stem Roots usually Originate at a Node – Arise from Quaternary Roots Photo by Jared Deckard, Natural Resource Specialist, Pomme de Terre Lake Brace & Prop Roots • Types of Adventitious Roots Monocot vs. Dicot • Fibrous Root System • Root System Develops from Adventitious Roots • Scattered Vascular System around Perimeter of Stele • Taproot System • 1° Root Persists, Produces Branches & Continues as main Root of Plant • Vascular System in a Cross in the Center of the Stele Root Structure • Roots Grow from Meristems Near the Tip of Roots Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) & WH Freeman (www.whfreeman.com), used with permission. http://www.lima.ohio-state.edu/academics/biology/archive/roots.html 2 9/15/2011 • Root Cap Is at Tip • Being Regenerated by the Root Tip It Protects • Above Root Cap Is an Apical (Tip) Meristem where Cells Divide fairly Rapidly – Cells Deposited to the Sides, Leaving Thin GelLike Coating on Soil Particles – High Energy Process – Cells Actively Divide to Produce more Cells – Dividing Cells Are Protected by the Root Cap – Some Cells Are Used in the Root Cap – Some Cells Become Root Tissues • 20-30% of Photosynthetic Energy! http://www.lima.ohio-state.edu/academics/biology/images/onioncap.jpg http://www.botany.hawaii.edu/faculty/webb/BOT410/Roots/ApicalMeristems.htm • Above Meristem Is Zone of Elongation http://www.lima.ohio-state.edu/academics/biology/images/onioncap.jpg • Root Hairs Develop from Epidermal Cells • Once Epidermal Cells Cease Elongation, they Produce Tiny Extensions into Soil Area • Up to 200 Root Hairs/mm2 of Root – 1 to 10mm Long – Newly-Formed Cells Take on Water & Elongate to Mature Size – Primary Function Is to Increase Root Length • Above Elongation Zone Is Differentiation Zone or Zone of Maturation http://www.lima.ohio-state.edu/academics/biology/images/zeahair.jpg • Root Hairs Greatly Increase the Surface Area of a Root • 1-Month-Old Rye Plant = 14 Billion Root Hairs with Surface Area of ~4,300 ft2 • Reach Full Size in a few Hours • Essential for Rapid Absorption of Water & Nutrients • In Typical Soil, Water mostly Is Thin Film Surrounding every Microscopic Soil Particle • Root Hairs Absorb this Water • Water Diffuses Molecule by Molecule – Through the Root Hair's Cell Membrane – Toward the Main Roots – Then Enters Xylem http://www.backyardnature.net/roots.htm http://www.rsbs.anu.edu.au/profiles/Brian_Gunning/Web%20PCB/Ch%2002%20Intr oduction%20to%20Plant%20Cells/Topic%203%20AS&V%20Cells/02%2003%2001.htm Bacterial cells, each less than one-thousandth of a millimetre long, are shown stained green on a soil particle. http://www.grdc.com.au/growers/gc/gc48/soil2.htm 3 9/15/2011 Root Anatomy • Cross-Section in Maturation Zone Shows Cells Have Differentiated • Outermost Cells Called Epidermis – Single Layer of Cells on the Root Surface – Absorb Water & Nutrients • Next Is the Cortex – Loosely Packed Cells – Can Be several Layers Thick – Conduct Water & Nutrients to Vascular Bundle – Stores Food & Nutrients for the Root – Specialized Functions http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm • Next Is Endodermis – Single Layer of Cells that Separates the Vascular Bundle from Cortex – Regulates Types of Absorbed Nutrients Allowed to Enter Vascular Cylinder http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm The Pathway of Water in Roots Symplast—Living Portion of Cells Apoplast—Spaces between Cells http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm Vascular Cylinder Tissues • Pericycle – Separates the Xylem & Phloem – Layer of Meristematic Cells where Branch Roots Develop • Stele – The Root Center Tissues including the Pericycle, Phloem & Xylem – Stele Diameter Is Larger in Monocots than in Dicots http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm Video http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html • Vascular System – Very Center of Root – Made up of Phloem & Xylem – Monocots • Xylem & Phloem Are Separate • Form Ring around the Center of the Root – Dicots • Phloem Surrounds & Eventually Is Outside the Xylem • Xylem will Be in the Very Center of the Root http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm 4 9/15/2011 • Pith – Found in the Center of a Monocot • Cambium – Cells can Divide to Produce 2° Growth in Perennial Plants – Found only in Dicots – Not Important in Annual Plant Plants Root Functions • Water & Nutrient Uptake – Most Uptake Occurs near Root Tip, through Root Hairs – 80% Absorption Occurs in Top 18 Inches of Soil – Plant Management Practices will Affect Uptake Zones – Region of Greatest Root Volume not always Area of Greatest Water/Nutrient Uptake • Depends on the Plant Species’ Rooting Pattern – Root Does not ‘Grow toward’ Water & Nutrients http://ghs.gresham.k12.or.us/science/ps/sci/ibbio/plants/notes/introot.htm • Water & Nutrient Transport – Once Water Enters Root, Moves through Cortex to Endodermis, through Endodermis to Pericycle & then to Xylem – From Xylem, Moves Rapidly upward in Plant to Stems & Leaves, Carrying Nutrients with It – Injury to Roots can Reduce/Prevent this Flow, Hurting Above-Ground portions of Plant • Support & Anchoring – Roots Provide Support for Upright Stem Portions of Plants & Help Hold the Plant in the Soil against Wind & Rain • Storage – Most of Carbohydrates Transported to Roots Are Used for Active Root Growth, but some Crops will Store in their Roots Carbohydrates for later Growth/Regrowth – Stored Carbohydrates Allow Plants to Produce New Shoot Growth • Symbiotic Relationships with Microbes Super roots with Frankia Frankia, nitrogen-fixing bacteria that form associations with some plants http://www.laspilitas.com/advanced/advroots.htm 5 9/15/2011 Rhizobium • • • • • • Azospirillum Nitrogen-Fixing Species of Bacteria Symbiotic Relationship with Legumes N-Fixing Enzyme Nitrogenase Converts Atmospheric N into Ammonia Gives N to Plant Plant Gives Food to Bacteria • Nitrogen-Fixing Genus of Bacteria in many Grasses including Grain Crops (Photo: a cross-section of a root nodule--a tiny lump in which Rhizobium bacteria would do their clean-up work. Each nodule is occupied by about a billion of the rod-shaped microbes.) http://www.parksideorchids.com/images/Supplies/phyton.jpg http://www.ars.usda.gov/is/kids/environment/story3/rhizobium.htm http://www.patentlens.net/daisy/bioforge_bioindicators/3201/version/default/part/ImageData/data/Rice%20Azospirillum.jpg Frankia • Many secondary pioneer species are associated with Frankia. In California these include; Datisca glomerata, Frankia fixes nitrogen from the air & produces secondary chemicals that feed friendly associated free living bacteria & fungi. The plant-mycorrhiza-frankia Tripartite relationship often becomes a multi-layered community of associated free living & plant related organisms that protect & support each other. The relationships are Ceanothus, Alnus, Cercocarpus, Myrica, Purshia, Cowania, Chamaebatia, & Shepardia species. • Nitrogen • Defense • Increase # Root Hairs • Mineral & Water Uptake • Transport of Hormones through Roots • http://www.laspilitas.com/advanced/pictures/ceanothus_frankia.jpg complex with only the most obvious presently recognized. The different associated organisms are responsible for root hormones, pathogen control, nematode control, root exploration, plant community resource sharing, mineral mining, water retention & many more. The plants become increasingly instable as these organisms are replaced with non-supportive or parasitic pathogens or weedy organisms, including weedy plants. These problems can be very difficult to diagnose as everything is interrelated, & human intervention can often make the problem worse. Ceanothus get branded as short lived because the mychorriza-frankia & associates are not properly allowed to develop & grow. Ceanothus can live for a hundred or more years in the wild, & commonly for twenty to fifty years in a garden, if the appropriate Ceanothi are planted & left alone. Watering & fertilizing the plants more than required fools the plant into thinking that they do not need friends & can do all things themselves. The plants, if they do not die that day from pathogens, grow fast & robust, then die of pathogens. Frankia on the roots of Shepherdia argetea. http://www.laspilitas.com/classes/Frankia.html • Propagation (Creeping) •Mycorrhizae • CREEPING OR HORIZONTAL ROOTS - Are lateral branch roots. These are true roots, arising from a vertical root, usually an elongated taproot, & lack nodes & leaves. Adventitious buds may form at any point along these roots & produce new plants by sending up leafy shoots. Creeping roots can penetrate to a much greater depth than creeping below cultivating depths, & produce new deeper, horizontal branches when the upper ones are destroyed. Also, the horizontal roots can grow straight downward at any point, thus establishing very deep, extensive root systems, which are virtually impossible to eradicate. stems. Most of the taproot may extend http://www-mykopat.slu.se/ Newwebsite/mycorrhiza/kantarellfiler /bilder/C.GIF • http://ic.ucsc.edu/~wxcheng/envs161/Lecture8/ http://www.uapress.ari zona.edu/onlinebks/we eds/general.htm Some of the worst prohibited noxious weeds reproduce by creeping roots, as Russian knapweed (Centaurea repens), hoary cress (Cardaria draba), field bindweed (Convolvulus arvensis), Canada thistle (Cirsium arvense), silverleaf nightshade (Solanum elaeagnifolium), & http://www.ca.uky.edu/agc/pubs/pat/pat1-6/10.jpg blueweed (Helianthus ciliaris). 6 9/15/2011 Extent of Root Growth • Root Dry Weight Is usually 1/3 to ¼ of Total Plant Dry Weight (may be more) • Root Surface Area Is at Least 20 to 30 Times Greater than Leaf & Stem Surface Area • Knowing Extent of Root System Aids in Water & Fertilizer Placement • Geotropism Factors Affecting Root Growth • Tropism – When Growth Responds to Environmental Stimuli • Thermotropism – Roots Grow Downward, with Gravity (Positive Geotropism) – Due to Different Amounts of Plant Hormones Called Auxins in different Parts of a Cell – Upper Side of Horizontal Root Grows more, Causing Root Tip to Turn Downward • Phototropism – Roots Grow Better in certain Temperatures • Hydrotropism – Roots Grow more Rapidly in Favorable Moisture Environment http://www.kalamazoomi.com/photo/Okinawa/banyantree-a-roots.JPG – Roots Grow away from Light (Negative Phototropism) http://www.bioschool.co.uk/bioschool.co.uk/images/pages/geotropism_JPG.htm http://jp.encarta.msn.com/media_461516459_761568511_-1_1/content.html • Genetics http://www.4am.org/photos/kools/Tree%20Roots.jpg • Soil Fertility & pH – Determines Basic Structure of Root Systems – Can Be Enhanced by Plant Breeding & Selection & by Genetic Engineering – Roots Grow Better, more Branching & Spread, in a Fertile Soil Compared to less Fertile Soil – Roots Do not Grow toward Nutrients – Excess Nutrients in Soil – pH beyond Optimum Ranges Result in Reduced Root Growth • Soil Moisture Level • Soil Physical Condition – Roots can Grow only where Root Pressure Is Greater than the Physical Pressures Exerted against the Roots Tillage pans. http://ianrpubs.unl.edu/soil/g831.htm www.abc.net.au/landline/ stories/s132488.htm groups.ucanr.org/ kernag/Salinity/ 7 9/15/2011 • Soil Aeration • Soil Temperatures in Root Zone – Optimum usually Cooler than for above-Ground Plant Portions – Less Temp Fluctuation than Above Ground – Temperatures above Optimum? – Temperatures below the Optimum? – Temp Affects Root Thickness & Branching – Effects of Moisture? – Effects of Soil Color? – Effects of Plant Canopy or Other Covering? – 20-25% of Soil Pore Space should Be Air – Oxygen Needed for Respiration – Reduced Growth if Soil Aeration < 10% • Except Hydrophytes – Anaerobic Microorganisms may Produce Toxins – CO2 in Soil Air often Higher than in AboveGround Air www.martiansoil.com/ archives/week_2004_03_14.php Specialized Roots & Vegetative Propagation • Creeping Roots – Dicots – Roots Initiate Adventitious Shoots – May Grow Deeply – New Shoots Independent of Parent Plant – Killing Shoots Encourages Formation of New Shoots ipcm.wisc.edu/uw_weeds/ infosys.ars.usda.gov/ images/CanadaThistle03.jpg Weeds/Bindweed/sld006.htm http://www.btny.purdue.edu/Pubs/WS/CanadaThistle/roots.jpg http://ianrpubs.unl.edu/weeds/graphics/spurge6a.jpg • Tuberous Roots – Abruptly Thickened Roots – Appear to Be Tap Roots, but often Are Types of 2° or Adventitious Roots 8