Download Nitrogen fixing bacteria

PLANT NUTRITION
•The soil and nutrients
Plant Macronutrients
(each may greatly exceed 1% dry weight of healthy plant)
•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+ [non-mineral]
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
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
•Zinc (Zn2+) chorophyll formation; activates
some enzymes
Copper-deficient plant with bluegreen, curled leaves
•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
Topsoil
Subsoil
A soil’s profile. The
A, B, and C horizons
Weathering
can sometimes be
seen in roadcuts such
bedrock
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 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; 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
Topsoil Mixture of broken-down
rock of various textures
Subsoil Less organic matter,
less weathering than topsoil
Weathering bedrock Mostly
partially broken-down rock –
parent material for upper
layers
SOIL HORIZONS IN ROADCUT
Most roots occur in the topsoil
Surface litter
Top soil
Root nodules:
Sub soil
nitrogen fixing
bacteria
Bedrock
Fungus
Diversity of
Life in a Fertile
Soil
Bacteria
(Solomon 1999)
Mite
Springtail
Nematode
Protozoa
Root
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; water that
percolates down through soil carries
with it dissolved nutrients (leaching)
Pore space, soil, air and water; the degree to which plants and soil organisms
are sustained depends on the degree to which soils are moist and
aerated(Solomon 1999)
Soil Particles
Soil Air
Soil water
with dissolved
minerals
(Solomon 1999)
Three of the most important gases in soil are:
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
Solutes (dissolved, osmotically active molecules)
cytoplasm
membrane
soil
Plants acquire their
nutrients and water
primarily through
their roots
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
•Mineral 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
Solubility of three mineral nutrients as a function of pH (Keaton and Gould 1993)
Acid pH
4
Neutral pH
Alkaline pH
7
Plants are affected by soil pH for two main reasons:
-solubility of certain minerals varies with pH
-ability of soil to bind cations decreases with increasing soil acidity
Atmospheric acid precipitation decreases soil pH (increases acidity)
10
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 charged
nutrient mineral ions are attracted to the
negatively charged soil particles
In acidified soils, hydrogen ions displace the
cations. Aluminum ions released when the soil
becomes acidified also adhere to soil
How acidity alters soil chemistry.
N2 + 8e- + 8H+ + 16 ATP
2NH3 + H2 + 16 ADP +16 P i
reduction of N2
oxidation of NH4
Llife 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.
Solomon 1999
Cation Exchange