Plant Nutrition
(Ch. 37)
Physiological adaptation
Dogs pee on trees…Why don’t trees pee on dogs?
NH3
animal waste
plant nutrient
Nutritional needs
• Autotrophic does not
mean autonomous
– plants need…
• sun as an energy
source
• inorganic compounds
as raw materials
– water (H2O)
– CO2
– minerals
Macronutrients
• Plants require these nutrients in relatively
large amounts
– C, O, H, N, P, K, Ca, Mg, S
For what & from where?
C
macromolecule synthesis
CO2
O
macromolecule synthesis
CO2
H
macromolecule synthesis & proton pumps
H2O
N
protein & nucleic acid
synthesis
to make
all plant proteins
soil
P
nucleic
acids,a ATP,
phospholipids
soil growth
establish
strong
root system in young plants,
K
stomate
water
balance
soil (ie. carrots)
Flowers,control,
absorption
of water,
strong roots, root crops
Ca
cell wall & membrane
regulation
soil
Cell walls, structure,
nutrient and
soil conditioner
Mg
chlorophyll
soil
S
proteins, enzymes
soil
Local Long Island soil issues
Quartz
silica based soils
- low in P
- can be acid
Acid soils bind up
mineral ions
pH by adding lime
Granite
Micronutrients
• Plants require in very small amounts
– Cl, Fe, Mn, Bo, Zi, Ni, Mb
– primarily cofactors for enzyme function
Nutrient deficiencies
• Lack of essential nutrients
– exhibit specific symptoms
• dependent on
function of nutrient
• dependent on
solubility of nutrient
• Mineral deficiency symptoms depend not only on the role of the nutrient
but also on its mobility within the plant. If a nutrient moves about freely,
symptoms will show up first in older organs because young, growing
tissues have more “drawing power” for nutrients in short supply. For
example, magnesium is relatively mobile and is shunted preferentially to
young leaves. Therefore, a plant starved for magnesium will show signs of
chlorosis first in its older leaves. The mechanism for preferential routing is
the source–to–sink translocation in phloem as minerals move along with
the sugars to the growing tissues. In contrast, a deficiency of a mineral
that is relatively immobile will affect young parts of the plant first. Older
tissues may have adequate amounts, which they are able to retain during
periods of short supply. For example, iron does not move freely within a
plant, and an iron deficiency will cause yellowing of young leaves before
any effect on older leaves is visible.
• Deficiencies of nitrogen, phosphorus, and potassium are most common.
Shortages of micronutrients are less common and tend to occur in certain
geographic regions because of differences in soil composition. The
symptoms of a mineral deficiency are often distinctive enough for a plant
physiologist or farmer to diagnose its cause
Magnesium deficiency
• Symptoms
Take 2
fertilizer pellets
& call me in
the morning
– chlorosis = yellowing of leaves
– Why? What is magnesium’s function?
Chlorophyll
Why does magnesium
deficiency cause chlorosis?
The chlorosis shows up in older
leaves first, because plant moves
Mg+ to newer leaves. Why?
The role of soils
Agronomists
really dig dirt!
• Plants are dependent on soil quality
– texture / structure
• relative amounts of various sizes of soil particles
– composition
• organic & inorganic chemical components
• fertility
Importance of organic matter
• Topsoil
So don’t rake
– most important to plant growth
your lawn or
bag your leaves
– rich in organic matter
• humus
– decomposing organic material
» breakdown of dead organisms, feces, fallen
leaves & other organic refuse by bacteria &
fungi
– improves soil texture
– reservoir of minerals
– organisms
• 1 tsp. of topsoil has ~5 billion bacteria
living with fungi, algae, protists, insects,
earthworms, nematodes
Soil health as a global issue
Not taking care of soil health has
far-reaching, damaging
consequences
– 1920’s Dust Bowl
– lack of soil conservation
• growing the same crop
year after year (wheat)
• grazing by cattle
• bare ground exposed to
wind erosion in winter
• drought
Soil health as a global issue
• Soil conservation & sustainable agriculture
– maintaining healthy environment
– sustainable production of food supply
– economically viable farming industry
“A sustainable agriculture does not deplete soils or people.”
– Wendell Berry
contour plowing
cover crops
crop rotation
Fertilizers
• “Organic” fertilizers
– manure, compost, fishmeal
• “Chemical” fertilizers
– commercially manufactured
– N-P-K (ex. 15-10-5)
• 15% nitrogen
• 10% phosphorus
• 5% potassium
What are the
political, economic,
environmental
issues?
Your next Current event!
Nitrogen uptake
• Nitrates
– plants can only take up nitrate (NO3-)
• Nitrogen cycle by bacteria
– trace path of nitrogen fixation!
root
What will the plant use N for?
Soybean root nodules
• N fixation by Rhizobium bacteria
– symbiotic relationship with bean family
(legumes)
Increasing soil fertility
• Cover crops
Plow it under?
Why would you
that?
– growing a field of plants just to
plow them under
• usually a legume crop
• taking care of soil’s health
– puts nitrogen back in soil
A farmer…
outstanding
in his field?
erosion control, too
Some plant oddities…
2006-2007
Parasitic plants
• tap into host plant vascular system
Indian pipe
Mistletoe
Plants of peat bogs
• High acid environment
– most minerals & nutrients bound up & are not
available to plants
• must find alternative sources of nutrients
Carnivorous
plants
Sundew
Venus fly trap
Pitcher plant
Are they really
carnivores?
Pitcher plant
Uses of peat
Any Questions??
Review Questions
1. The inorganic compound that contributes most
of the mass to a plant’s organic matter is *
A.
B.
C.
D.
E.
H2O.
CO2.
NO32.
O2.
C6H12O6.
2. You are conducting an experiment on plant growth.
You take a plant fresh from the soil and it weighs 5
kg. Then you dry the plant overnight and determine
the dry weight to be 1 kg. Of this dry weight, how
much would you expect to be made up of inorganic
minerals?
A. 50 grams
B. 500 grams
C. 1 kg
D. 4 kg
E. 5 kg
• we can rule out C, D , and E and because the
dry weight of any plant is going to be
mostly cellulose ( a polymer of glucose) we
can pretty much be assured half of the dry
weight is not going to be from inorganic
minerals and ions. The only choice that makes
any sense at all is 50grams. No calculations
needed
This figure shows the
results of a study to
determine the effect
of soil air spaces on
plant growth. Use
these data to answer
the following
question.
3. The best explanation for the shape of this growth
response curve is that
A. the plant requires air in the soil for photosynthesis.
B. the roots are able to absorb more nitrogen (N2) in high
levels of air.
C. most of the decrease in weight at low air levels is due
to transpiration from the leaves.
D. increased soil air produces more root mass in the soil
but does not affect the top stems and leaves.
E. the roots require oxygen for respiration and growth.
4. Carnivorous plants have evolved mechanisms that
trap and digest small animals. The products of
this digestion are used to supplement the plant's
supply of
A.
B.
C.
D.
E.
energy.
carbohydrates.
lipids and steroids.
minerals.
water.
• Are some essential elements more important
than others? Explain.
No, because even though macronutrients are
required in greater amounts, all essential
elements are necessary for the plant to
complete its life cycle.
• Can a single leaf be used to diagnose all of a
plant’s mineral deficiencies? Explain.
a. No, because deficiencies of nutrients that are
more mobile show up first in older leaves,
whereas deficiencies in nutrients that are less
mobile show up first in younger leaves.