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o Micronutrient: elements that are needed in only small amounts Function mainly as cofactors in chemical reactions Limiting nutrient: relative availability in environment is less than plants need for it 33 Concept 37.3: Plant nutrition often involves relationships with other organisms Soil Bacteria and Nitrogen Availability
o Nitrogen fixation: bacteria convert N2 from the atmosphere to NH3 o Ammonification: bacteria convert Ncontaining organic material to NH4+
o Nitrification: bacteria convert NH4+ to NO3 o Denitrification: bacteria convert NO3 to N2 o Figure 37.10 o Two examples of plants with mutualistic relationships with other organisms Symbiotic nitrogen fixation Mycorrhizae
o Bacteria and Symbiotic Nitrogen Fixation Symbiotic relationships with Nfixing bacteria provide some plants with a builtin source of fixed N (NH4+) Root nodules: Swelling along the root that have been infected by Rhizombium bacteria Figure 37.11a 34
o Inside each nodule, Rhizombium bacteria assume a form called bacteroids, contained within vesicles formed by root cell
o Rhizombium convert N2 into ammonium (NH4)
o Plant provides a lowO2 environment for Nfixation process Thick cell walls Leghemoglobin Figure 37.11b Root Nodules on Legumes
o Chemical signals sent between root and bacteria
o Bacteria move into the cortex, form bacteroids; stimulate g...
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- Spring '08