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PLANT NUTRITION
You Are What You Eat!
Essential Nutrients in Plants
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.
Availability of Soil, Water, and Minerals
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+.
Ammonium Production by Bacteria
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.
NitrificationConversion of NH4
- to NO3-
Assimilation of NO3-
The Nitrogen Cycle
Rhizobium Live as Symbiotes in Root Nodules as Bacteroids
Soybean Root Nodule
Another Symbiote - MycorrhizaeSymbiotic Fungi Aid in Water Absorption
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,
Indian Pipe
Carnivorous Plants
• Live in acid bogs where soil conditions are poor.
• Have trouble obtaining nitrogen.
• Supplement their nutrition with animals.
Venus Fly Trap Pitcher Plant
Sundew