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PLANT NUTRITION You Are What You Eat!
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Essential Nutrients in Plants
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Absorption of Nutrients
80-85% of herbaceous plant mass is water. More than 90% of absorbed water is lost through transpiration. The dry mass of plants comes from CO2. Organic substances account for 95% of dry mass: 5% is inorganic. Positively charged ions (cations) stick to soil particles. Roots use cation exchange to obtain cations. Anions are not tightly bound and leach away faster. Root hairs release H+ and CO2 into the soil.
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Availability of Soil, Water, and Minerals
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Plants Can’t Acquire N2 Directly
Approx. 80% of the atmosphere is nitrogen. N2 must be converted to NH4+ or NO3-. In ammonification, ammonifying bacteria release NH4- from organic material by decomposition. Nitrogen-fixing bacteria make NH4+ by nitrogen-fixation using nitrogenase complex. Only certain prokaryotes of the genus Rhizobium (root living) can fix nitrogen. Lightning and U.V. radiation can also generate NH4+.
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Ammonium Production by Bacteria
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Conversion of Ammonia Ammonia converts to the ammonium ion in soil.
Plants usually absorb nitrate, NO3-. Nitrification is the conversion (oxidation) of NH4+ to NO2- and then to NO3- by nitrifying bacteria. After absorption of by the roots, NO3- is reduced back to ammonium within the plant. NH4+ is converted to protein and other organic compounds. Export of nitrogen is via xylem. Dentrifying bacteria convert soil NO3- back to N2. It takes 8 ATP’s to produce one NH3 molecule.
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Nitrification Conversion of NH4- to NO3-
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Assimilation of NO3-
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The Nitrogen Cycle
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Rhizobium Live as Symbiotes in Root Nodules as Bacteroids
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Soybean Root Nodule
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Another Symbiote - Mycorrhizae Symbiotic Fungi Aid in Water Absorption
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Parasitic Plants Indian pipe obtain nutrients from the host tree by tapping into the host tree’s micorrhizae. Mistletoe projects haustoria to siphon xylem sap from vascular tissue of the host: Oaks and other trees. They are also photosynthetic. Epiphytes (air plants) are not parasitic. They derive nutrients from the air and rainfall. Examples are: Spanish moss (angiosperm), staghorn fern,
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Indian Pipe
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Carnivorous Plants Live in acid bogs where soil conditions are poor.
Have trouble obtaining nitrogen. Supplement their nutrition with animals.
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Venus Fly Trap Pitcher Plant
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Sundew
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