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