Download No Slide Title

PLANT NUTRITION
•The soil and nutrients
•Nitrogen metabolism
Mineral nutrients: essential
chemical elements absorbed from
the soil in the form of inorganic ions
mineral nutrients are available in
dissolved form -- in soil solution
Essential Plant Macronutrients
(required by plants in relatively large amounts -- at least 1 g/kg dry weight)
•Carbon (CO2) [non-mineral]
carbs, lipids, proteins, nucleic acids
•Hydrogen (H2O) [non-mineral]
carbs, lipids, proteins, nucleic acids
•Oxygen (CO2, H2O) [non-mineral]
carbs, lipids, proteins, nucleic acids
•Nitrogen (NO3-, NH4+)
proteins, nucleic acids...
•Phosphorus ( HPO4-, H2PO42-)
nucleic acids, phospholipids, ATP...
•Potassium (K+)
osmotic pressure; stomata opening, closing
•Sulfur (SO42-)
proteins, coenzymes...
•Calcium (Ca 2+)
cytoskeleton; membrane perm.
•Magnesium (Mg2+)
chlorophyll;
Magnesium deficiciency in a
tomato plant. Yellowing of leaves
(chlorosis) is the result of an
inability to synthesize chlroophyll,
which contains magnesium
Essential Plant Micronutrients
(in most plants, each comprises from less than one
ppm to several hundred ppm)
•Iron (Fe3+) cytochrome component; activates some
enzymes
•Manganese (Mn2+) amino acid formation, activates
some enzymes,
•Copper (Cu2+) component of many redox and lignin
biosynthetic pathways
Copper-deficient plant with bluegreen, curled leaves
•Zinc (Zn2+) chorophyll formation; activates some
enzymes
•Molybdenum (MoO43+) nitrogen fixation; nitrogen
reduction
•Chlorine (Cl-) osmotically active; required for
photosynthesis
•Boron (H2BO3, HBO32) cofactor in chlorophyll
synthesis
•Nickel (Ni2+) cofactor of nitrogen metabolism
enzyme
Manganese-deficient plant with
chlorosis (yellowing) between the
veins;
The role of soil in plant nutrition
Soils provide
-mineral nutrients
-water
-oxygen
-bacteria
-substrate for
attachment
Soil Profile. The A, B,
and C horizons can
sometimes be seen in
roadcuts such as this
one in Australia. The
upper layers
developed from the
bedrock. The dark
upper layer is home to
most of the living
organisms.
Soil Formation
soils form through
mechanical and
chemical weathering
of bedrock
Topsoil
Subsoil
Weathering
parent
bedrock
Topsoil Mixture of broken-down
rock of various textures; most
organic matter (living and
decomposing) occurs here.
Subsoil Less organic matter,
less weathering than topsoil
Weathering bedrock Mostly
partially broken-down rock –
parent material for upper
layers
SOIL HORIZONS IN ROADCUT
SOIL COMPOSITION
•Soil Highly weathered outer layer of
Earth’s crust, consists of mineral matter
and organic matter
•Minerals; elements bound as inorganic
compounds
•Mineral matter (sources); includes
clay, silt, sand, rock – mineral sources
•Organic matter; includes humus
SOIL FORMATION
•Mineral particles; millions of years of
weathering of rocks by biological and
physical processes
•Organic material; decomposition of
organic debris
SOIL HORIZONS IN ROADCUT
Most roots occur in the topsoil
Surface litter
Top soil
Root nodules:
Sub soil
nitrogen fixing
bacteria
Bedrock
Mite
Fungus
Diversity of Life in a
Fertile Soil
Bacteria
(Solomon 1999)
Springtail
Nematode
Protozoa
Root
Solutes (dissolved, osmotically active molecules)
cytoplasm
membrane
soil
Water potential across
plant membrane.
Water potential is the
pressure, created
across a
semipermeable
membrane, that leads
to the flow of water.
It’s the result of both
osmotic pressure and
water pressure
differences.
(Keaton and Gould 1993)
Nutrient uptake and availability
•Nutrients are exchanged as negative or positive ions
•Many mineral nutrients exist in soil as positively charged ions (cations)
bound to clay; clay particles have important role in nutrient uptake
•Mineral nutrients existing in soil as negatively charged ions are easily
leached from soil
Acid pH
4
Neutral pH
7
Alkaline pH
10
Solubility of three mineral nutrients as a function of pH
(Keaton and Gould 1993)
Important Factors That Influence Soil pH
•Chemical composition of the soil and bedrock affects pH
•Cation exchange that roots perform decreases pH of soil
•Cellular respiration of soil organisms, including decomposers,
decreases pH
•Acid precipitation sulfuric and nitric acids in atmosphere fall to
ground as acid rain, sleet, snow, fog decreases pH
Negatively
charged clay
particle
Negatively
charged clay
particle
In normal soil, positively
In acidified soils, hydrogen ions
charged nutrient mineral ions
displace the cations. Aluminum
are attracted to the negatively
ions released when the soil becomes
charged soil particles
acidified also adhere to soil
How acid alters soil chemistry.
N2 + 8e- + 8H+ + 16 ATP
2NH3 + H2 + 16 ADP +16 P i
All life on Earth depends on Nitrogen-fixation; carried out exclusively by certain
Nitrogen fixing bacteria that reduce N2 to NH3 through reaction sequence mediated by
one enzyme complex: nitrogenase
•Plants acquire nitrogen mainly as nitrate (NO3-), which is produced in the soil by
nitrifying bacteria that oxidize ammonium (NH4+) to NO3-
Throughout the chemical reactions of nitrogen fixation, the reactants are
bound to the enzyme nitrogenase, a reducing agent that transfers
hydrogen atoms to nitrogen to form the final product – ammonia (picks
up H+ in soil to form ammonium (NH4+)
Nitrogen Fixers
Oceans
• various photosynthetic bacteria, including cyanobacteria
Freshwater
•cyanobacteria
Nitrogen-fixing Cyanobacteria.
Terrestrial
•certain soil eubacteria
•Rhizobium bacteria living symbiotically in the root nodules of
legume plants
Nitrogen-fixing Cyanobacteria.
Soil Particles
Soil Air
Soil water
with dissolved
minerals
Wet soil; most pore space
is filled with water
Dry soil; thin film of water
is tightly bound to soil
particles
Pore space, soil, air and water
(Solomon 1999)
Soil Particles
Soil Air
Soil water
with dissolved
minerals
Three important gases in soil
Oxygen (O2) required by soil organisms for aerobic respiration
Nitrogen (N2) used by nitrogen-fixing bacteria and
Carbon Dioxide (CO2), a product of aerobic respiration
Pore space, soil, air and water
(Solomon 1999)
Solomon 1999
Cation Exchange