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-, H2PO4
2-) 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
•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
Copper-deficient plant with blue-green, curled leaves
Manganese-deficient plant with chlorosis (yellowing) between the veins;
Topsoil
Subsoil
Weathering parent bedrock
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.
Soils provide
-mineral nutrients-water-oxygen-bacteria-substrate for attachment
The role of soil in plant nutrition
Soil Formation soils form through mechanical and chemical weathering of 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 HORIZONS IN ROADCUT
SOIL FORMATION•Mineral particles; millions of years of weathering of rocks by biological and physical processes
•Organic material; decomposition of organic debris
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
Most roots occur in the topsoil
Surface litter
Top soil
Sub soil
Bedrock
Fungus
BacteriaProtozoa
Mite
Springtail
Nematode
Root
Root nodules:
nitrogen fixing bacteria
Diversity of Life in a Fertile Soil
(Solomon 1999)
Solutes (dissolved, osmotically active molecules)
cytoplasm membrane soilWater 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 Neutral pH Alkaline pH
4 7 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
How acid alters soil chemistry.
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
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
-
N2 + 8e- + 8H+ + 16 ATP 2NH3 + H2 + 16 ADP +16 P i
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
Terrestrial •certain soil eubacteria •Rhizobium bacteria living symbiotically in the root nodules of legume plants
Nitrogen-fixing Cyanobacteria.
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
Pore space, soil, air and water(Solomon 1999)
Three important gases in soil Oxygen (O2) required by soil organisms for aerobic respirationNitrogen (N2) used by nitrogen-fixing bacteria and Carbon Dioxide (CO2), a product of aerobic respiration
Cation Exchange
Solomon 1999
