Transcript

PLANT NUTRITION•The soil and nutrients•Essential mineral nutrients •Nitrogen metabolism

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-, 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

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 bedrock

A soil’s 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.

The role of soil in plant nutrition

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; includes clay silt, sand, rock – mineral sources

•Organic matter; includes humus

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

Sub soil

Bedrock

Fungus

BacteriaProtozoa

Mite

Springtail

Nematode

Root

Root nodules:

nitrogen fixing bacteria

Diversity of Life in a Fertile Soil

(Solomon 1999)

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 respirationNitrogen (N2) used by nitrogen-fixing bacteria and Carbon Dioxide (CO2), a product of aerobic respiration

Solutes (dissolved, osmotically active molecules)

cytoplasm membrane soilPlants 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

Acid pH Neutral pH Alkaline pH

4 7 10

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)

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 acidity 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

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

-

N2 + 8e- + 8H+ + 16 ATP 2NH3 + H2 + 16 ADP +16 P i

reduction of N2

oxidation of NH4

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.

Cation Exchange

Solomon 1999


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