Nitrogen Fixation and Agriculture- Crop rotation- Takes advantage of the agricultural benefits ofsymbiotic nitrogen fixation- Year 1: A non legume plant such as maize is planted- Year 2: A legume is planted=> Restore the concentration of fixed nitrogen in the soilFungi and Plant Nutrition- Mycorrhizae are mutualistic associations of fungi androots- The fungus benefits from a steady supply of sugar fromthe host planthttp://archive.bio.ed.ac.uk/jdeacon/FungalBiology/mycorhiz.htm http://www.bbc.com/news/science-environment-22462855http://ecomyc.com/mycorrhizae/The host plant benefits because the fungus increases thesurface area for water uptake and mineral absorptionMycorrhizal fungi also secrete growth factors that stimulateroot growth and branching- Two the most important groups- Ectomycorrhizae- 10% of plant familiespine, oak, birch, and eucalyptus- Arbuscular mycorrhizae- In about 85% of plant species,-Including grains and legumesFigure 37.13a (a) EctomycorrhizaeCortexEpidermis Mantle (fungal sheath)EpidermalcellEndodermisFungalhyphaebetweencorticalcells (LM) 50 μmMantle(fungal sheath)(Colorized SEM)1.5 mmIn ectomycorrhizae, the mycelium of the fungus forms adense sheath over the surface of the rootThese hyphae form a network in the apoplast, but do notpenetrate the root cellsFigure 37.13b(b) Arbuscular mycorrhizaeCortical cellEndodermisFungalvesicleCasparianstripArbusculesPlasmamembrane (LM)10 μmCortexEpidermisFungalhyphaeRoothairArbuscular mycorrhizae: Association of a fungus with plantroots where the hyphae grow into tubes formed by theinvagination of the plant cell’s membranesEpiphytes, Parasitic Plants, and Carnivorous Plants- Some plants have nutritional adaptations that useother organisms in non mutualistic ways- Three unusual adaptations are- Epiphytes- Parasitic plants- Carnivorous plants- An epiphyte grows on another plant and obtainswater and minerals from rainFigure 37.14aStaghorn fern, an epiphyteAn epiphyte grows on another plant and obtains water and minerals fromrainhttp://picssr.com/tags/epiphyten/page2A.CzerednikEpiphytesFigure 37.14b Parasitic plantsMistletoe, a photosynthetic parasiteRafflesia, a non-photosyntheticparasiteIndian pipe, a non-photosyntheticparasite ofmycorrhizaeThey hurt but do not kill their hostLathraea clandestina(purple toothwort)