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Roots • Anchorage • Storage • Absorption • Conduction Root Systems: Definitions • Taproot system: A central, downward-growing, dominant root (the “taproot”), with numerous, highly branched lateral roots permeating the surrounding soil. The tap root itself develops from the radicle (embryonic root). • Fibrous root system: Numerous, slender, roots of roughly equal size.to form a mass of fine roots. No dominant, central root; radicle ceases development . Develops initially from adventitious roots that emerge • Adventitious = originating from an “unusual” source/location . – Adventitious roots are roots that originate from stems or leaves instead of developing from the radicle or preexisting root. – Adventitious buds = buds that form on the roots or stem internodes of some plants, instead of the “usual” axillary or terminal locations on the stem. Taproot Systems • Taproot and downward-growing laterals can penetrate deep into soil (~4 m, up to ~68 m) • Tap into deep water sources. • Deep=penetrating taproots tend occur in arid/desert habitats. • Majority of actively absorbing and growing roots are within 2 feet of soil surface. • “Feeder roots” • Absorb nutrients from decomposing organic matter, surface and rain water. Taproot Systems Fibrous Root Systems Adventitious roots in corn Develop from the lower nodes of the stem. Epidemal Root Hairs • The epidermis of roots is specialized for absorption of water and minerals. • Root hairs – outgrowths from epidermal cells – as a root grows, the root hairs penetrate the surrounding volume of soil ( Corn Root Tip Dicot root Monocot Root Casparian Strip Specialized Roots • Storage roots: Food reserves • Aerial roots: adventitious roots, originate and function (at least partly) aboveground. – Pneumatophores: aid gas exchange – Prop and Buttress roots: structural support of trunks, stems, branches – Photosynthetic & water storing roots: epiphytic orchids • • • • • • Contractile roots: Climbing roots: Clonal reproduction: Haustoria: parasitic feeding structures Mycorrhizae: mutualism with fungi in the soil Nitrogen-Fixing nodules: mutualism with Nitrogen-fixing bacteria Symbioses (Symbiotic relationships) Interaction between 2 organisms (plant-plant, plant-microbe, plant-fungus, etc.) Commensalism: one benefits, the other unaffected Parasitism: One (the parasite) benefits, the other (the host) is “harmed” in some way. Mutualism: Mutually beneficial interaction •These interactions typically involve modified/specialized root structures. Epiphytes: Commensal Plants • Most common in relatively moist/humid environments, with dense vegetation/tree canopy that limits light penetration. • By living on trees, epiphytes can receive more sunlight. • Tree surface is actually an arid environment. • Epiphyte roots often have “drought adaptive” modifications: e.g. velamen in orchids (water storage) • Some epiphytes lack leaves (=pathways for water loss!) • Instead: aerial roots adapted for photosynthesis Mycorrhizae: plant-fungus mutualism Endomyccorhizae Ectomyccorhizae Haustoria