plant nutrition the soil and nutrients nitrogen metabolism mineral nutrients: essential chemical...

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  • PLANT NUTRITIONThe soil and nutrientsNitrogen metabolismMineral nutrients: essential chemical elements absorbed from the soil in the form of inorganic ionsmineral 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 acidsHydrogen (H2O) [non-mineral] carbs, lipids, proteins, nucleic acidsOxygen (CO2, H2O) [non-mineral] carbs, lipids, proteins, nucleic acidsNitrogen (NO3-, NH4+) proteins, nucleic acids...

    Phosphorus ( HPO4-, H2PO42-)nucleic acids, phospholipids, ATP...Potassium (K+) osmotic pressure; stomata opening, closingSulfur (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 enzymesManganese (Mn2+) amino acid formation, activates some enzymes,Copper (Cu2+) component of many redox and lignin biosynthetic pathwaysZinc (Zn2+) chorophyll formation; activates some enzymesMolybdenum (MoO43+) nitrogen fixation; nitrogen reduction Chlorine (Cl-) osmotically active; required for photosynthesisBoron (H2BO3, HBO32) cofactor in chlorophyll synthesisNickel (Ni2+) cofactor of nitrogen metabolism enzymeCopper-deficient plant with blue-green, curled leavesManganese-deficient plant with chlorosis (yellowing) between the veins;

  • Topsoil


    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 attachmentThe role of soil in plant nutritionSoil 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 topsoilWeathering bedrock Mostly partially broken-down rock parent material for upper layers SOIL HORIZONS IN ROADCUT

  • SOIL HORIZONS IN ROADCUTSOIL FORMATIONMineral particles; millions of years of weathering of rocks by biological and physical processesOrganic material; decomposition of organic debrisSOIL COMPOSITIONSoil Highly weathered outer layer of Earths crust, consists of mineral matter and organic matterMinerals; elements bound as inorganic compoundsMineral matter (sources); includes clay, silt, sand, rock mineral sourcesOrganic matter; includes humus

  • Most roots occur in the topsoil

  • Surface litter

    Top soil

    Sub soilBedrock

    FungusBacteriaProtozoaMiteSpringtailNematodeRootRoot nodules:nitrogen fixing bacteriaDiversity 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. Its the result of both osmotic pressure and water pressure differences.(Keaton and Gould 1993)

  • Nutrient uptake and availabilityNutrients are exchanged as negative or positive ionsMany mineral nutrients exist in soil as positively charged ions (cations) bound to clay; clay particles have important role in nutrient uptakeMineral 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)

  • 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

  • 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: nitrogenasePlants 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 cyanobacteriaFreshwater cyanobacteria

    Terrestrial certain soil eubacteria Rhizobium bacteria living symbiotically in the root nodules of legume plants

    Nitrogen-fixing Cyanobacteria.

  • Nitrogen-fixing Cyanobacteria.

  • Soil ParticlesSoil AirSoil water with dissolved mineralsWet soil; most pore space is filled with waterDry soil; thin film of water is tightly bound to soil particlesPore space, soil, air and water(Solomon 1999)

  • Soil ParticlesSoil AirSoil water with dissolved mineralsPore 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 ExchangeSolomon 1999


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