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 (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 + ) 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

Essential 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;

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 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 Bacteria Protozoa 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 soil Water 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 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 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 ATP 2NH 3 + H 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 (NH 4 + )

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.

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 (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

Cation Exchange Solomon 1999