Transcript Ch 37 Lecture

Chapter 37
Plant
Nutrition
Uptake of nutrients in plants: Leave and roots
I.
Nutrients
A. Essential: required for the plant to grow
& life cycle
B. Macronutrients- required in large
amounts. Ex. carbon, oxygen,
hydrogen, nitrogen, sulfur, phosphorus,
potassium, calcium, magnesium
C. Micronutrients- required in small
amounts; cofactors of enzyme action.
Ex. chlorine, iron, boron, manganese,
zinc, copper, molybdenum, nickel
D. Deficiency
• chlorosis (lack of magnesium;
chlorophyll production)
E. Dry weight of plant = 95%
organic, 5% inorganic
II. Soil
A. Determines plant growth & variety (also
climate)
B. Soil horizons:
Loams: The most
fertile topsoil
B. Soil Horizons: O, A, E, B, C, R
O Horizon - The top, organic
layer of soil, made up mostly of
leaf litter and humus
(decomposed organic matter).
A Horizon - The layer called
topsoil; Seeds germinate and
plant roots grow in this darkcolored layer. It is made up of
humus (decomposed organic
matter) mixed with mineral
particles.
E Horizon - This eluviation
(leaching) layer is light in color;
It is made up mostly of sand
and silt, losing most of its
minerals and clay as water drips
through the soil (in the process
of eluviation).
B Horizon - Also called the
subsoil - It contains clay and
mineral deposits (like iron,
aluminum oxides, and calcium
carbonate) that it receives from
layers above it when
mineralized water drips from
the soil above.
C Horizon - Also called regolith:
It consists of slightly broken-up
bedrock. Plant roots do not
penetrate into this layer; very
little organic material is found
in this layer.
R Horizon - The unweathered
rock (bedrock) layer that is
beneath all the other layers.
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III. Nitrogen Fixation
A. The atmosphere is ~80% N2 . Plants
need nitrogen but cannot take nitrogen
gas directly out of the atmosphere.
1. Nitrogen must be converted to
ammonium (NH4+) or nitrate (NO3-)
to be absorbed by plants.
2. Some nitrogen is put into the soil when
dead organisms decompose in the soil.
 Microbes break down dead organisms
 However, some denitrifying bacteria
will convert NO3- to N2.
B. Nitrogen-fixing bacteria: bacteria that take
N2 from the atmosphere and convert it into
NH4+ and NO3-.
1. Nitrifying bacteria: convert NH4+ to NO32. Ammonifying bacteria: convert dead
organic material into NH4+.
THE NITROGEN CYCLE:
IV. Plant symbiosis, I
A. Rhizobium
bacteria (found
in root nodules in
the legume
family)
B. Mutualistic:
legume receives
fixed N2 
bacteria receives
carbohydrates &
organic materials
1. Roots emit
chemical
signals that
attract
Rhizobium.
The bacteria
then emit
signals that
elongate
root hairs
and form an
invagination
(infected
thread).
2. Bacteria
penetrate the
root cortex.
Root cells
divide,
and contain
vesicles with
bacteria
in them.
3. Growth
continues in
the cortex and
pericycle.
The two masses
fuse forming the
nodule.
4. The nodules
continue to
grow into the
vascular
tissue, which
supplies
nutrients to
the nodules.
Nodules
V. Plant symbiosis, II
A. Mycorrhizae (fungi)
modified roots
B. Mutualistic: fungus
receives sugar 
plant receives increased
root surface area and
increased phosphate
uptake
C. Two types:
ectomycorrhizae
• ensheaths
the root, woody
plants, trees,
pines
endomycorrhizae
(90% of plants)
•through cell wall
but not cell
membrane
(arbuscles)
Fungal Hyphae
in between plant
root cells of
ectomycorrhizae
Fungal hyphae branch
into the root cells, but
do not penetrate the
plasma membrane;
arbuscles
VI. Plant parasitism & predation
A. Mistletoe (parasite)- use haustoria to
siphon xylem sap from host tree
B. Epiphytes- autotrophic plant that
nourishes itself but grows on the surface
of another plant, usually on the branches
or trunks of trees (mosses)
C. Carnivorous
plants- glands
secrete digestive
juices
Mistletoe