2. PLANT NUTRITION The soil and nutrients Essential mineral nutrients Nitrogen metabolism

3. Plant Macronutrients (each may greatly exceed 1% dry weight of healthy plant) Carbon (CO 2 ) [non-mineral.] carbs, lipids, proteins, nucleic acids Hydrogen (H 2 O) [non-mineral.] carbs, lipids, proteins, nucleic acids Oxygen (CO 2, H 2 O) [non-mineral]carbs, lipids, proteins, nucleic acids Nitrogen (NO 3 -, NH 4 + [non-mineral] proteins, nucleic acids... Phosphorus ( HPO 4 -, H 2 PO 4 2- )nucleic acids, phospholipids, ATP... Potassium (K + ) osmotic pressure; stomata opening, closing Sulfur (SO 4 2- ) proteins, coenzymes... Calcium (Ca 2+ ) cytoskeleton; membrane perm. Magnesium (Mg 2+ )chlorophyll; Magnesium deficiciency in a tomato plant. Yellowing of leaves (chlorosis) is the result of an inability to synthesize chlroophyll, which contains magnesium

4. Plant Micronutrients (in most plants, each comprises from less than one ppm to several hundred ppm) Iron (Fe 3+ ) cytochrome component; activates some enzymes Manganese (Mn 2+ ) amino acid formation, activates some enzymes, Copper (Cu 2+) component of many redox and lignin biosynthetic pathways Zinc (Zn 2+ ) chorophyll formation; activates some enzymes Molybdenum (MoO 4 3+ ) nitrogen fixation; nitrogen reduction Chlorine (Cl-) osmotically active; required for photosynthesis Boron (H 2 BO 3, HBO 3 2 ) cofactor in chlorophyll synthesis Nickel (Ni 2+ ) cofactor of nitrogen metabolism enzyme Copper-deficient plant with blue- green, curled leaves Manganese-deficient plant with chlorosis (yellowing) between the veins

5. 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

6. 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

7. 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

8. Most roots occur in the topsoil

9. Surface litter Top soil Sub soil Bedrock Fungus Bacteria Protozoa Mite Springtail Nematode Root Root nodules: nitrogen fixing bacteria Diversity of Life in a Fertile Soil (Solomon 1999)

10. 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)

11. Soil Particles Soil Air Soil water with dissolved minerals (Solomon 1999) Three of the most important gases in soil are:  Oxygen (O 2 ) required by soil organisms for aerobic respiration  Nitrogen (N 2 ) used by nitrogen-fixing bacteria and  Carbon Dioxide (CO 2 ), a product of aerobic respiration

12. 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)

14. 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

15. 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)

16. 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

17. 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

18. Llife on Earth depends on Nitrogen-fixation; carried out exclusively by certain Nitrogen fixing bacteria that reduce N 2 to NH 3 through reaction sequence mediated by one enzyme complex: nitrogenase Plants acquire nitrogen mainly as nitrate (NO 3 - ), which is produced in the soil by nitrifying bacteria that oxidize ammonium (NH 4 + ) to NO 3 - N 2 + 8e - + 8H + + 16 ATP 2NH 3 + H 2 + 16 ADP +16 P i reduction of N 2 oxidation of NH 4

19. 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 (NH 4 + )

20. 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.

27. Cation Exchange Solomon 1999