Watch a Kansas Wheat Field Grow! Development of Agriculture critical to civilization Top three major human foods are grass seeds/fruit (grains) Wheat: Near East 9,000 years ago million Metric Tons 2008/09 global wheat production is projected PLANT NUTRITION

Watch a Japanese Rice Field Grow! Rice: Eastern China & Northern India 7,000 years ago million Metric Tons 2008/09 global rice production is projected

Visit the Iowa Corn Cam! Corn: Central Mexico 5,500 years ago 772 million metric tons 2008/09 global corn production is projected (U.S. ethanol is consuming roughly 13% of the corn produced in the world).

Overview: A Nutritional Network Every organism – Continually exchanges energy and materials with its environment For a typical plant – Water and minerals come from the soil, while carbon dioxide comes from the air

The branching root system and shoot system of a vascular plant – Ensure extensive networking with both reservoirs of inorganic nutrients

Plants require certain chemical elements to complete their life cycle Plants derive most of their organic mass from the CO 2 of air – But they also depend on soil nutrients such as water and minerals CO 2, the source of carbon for Photosynthesis, diffuses into leaves from the air through stomata. Through stomata, leaves expel H 2 O and O 2. H2OH2O O2O2 CO 2 Roots take in O 2 and expel CO 2. The plant uses O 2 for cellular respiration but is a net O 2 producer. O2O2 CO 2 H2OH2O Roots absorb H 2 O and minerals from the soil. Minerals

Macronutrients and Micronutrients More than 50 chemical elements – Have been identified among the inorganic substances in plants, but not all of these are essential A chemical element is considered essential – If it is required for a plant to complete a life cycle

Researchers use hydroponic culture – To determine which chemicals elements are essential TECHNIQUE Plant roots are bathed in aerated solutions of known mineral composition. Aerating the water provides the roots with oxygen for cellular respiration. A particular mineral, such as potassium, can be omitted to test whether it is essential. RESULTS If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and discolored leaves. Deficiencies of different elements may have different symptoms, which can aid in diagnosing mineral deficiencies in soil. Control: Solution containing all minerals Experimental: Solution without potassium APPLICATION In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is to identify essential elements in plants.

Criteria of essentiality (DI Arnon & PR Stout, 1939) 1.The element must be essential for normal growth or reproduction, which can not proceed without it. 2.The element cannot be replaced by another element. 3.The requirement must be direct, that is, not the result of some indirect effect such as relieving toxicity caused by some other substance.

C HOPKNS CaFe Mg Na Cl (Mighty good) (Not always) (Clean) With some apologies to Edward Hopper (American ) Nighthawks, 1942 Oil on canvas; 33 1/8 x 60 in. (84.1 x cm) CuMn CoZn MoB(y)!

Nine of the essential elements are called macronutrients – Because plants require them in relatively large amounts The remaining eight essential elements are known as micronutrients – Because plants need them in very small amounts Key to role elements play in plants for next two slide Structual Cofactors, osmotic relationships

C = carbon = Major structural component of organic molecules H = Hydrogen = Major structural component of organic molecules O = Oxygen = Major structural component of organic molecules; Final electron acceptor in Oxidative Phosphorylation P = Phosphorus = Important structural component of nucleic acids, phospholipids, coenzymes K = Potassium = Important cofactor of some enzymes, stomatal opening, membrane potentials, osmotic balance N = Nitrogen = Important structural component of nucleic acids, proteins, chlorophyll, some phytohormones S = Sulfer = Important structural component of some amino acids, forms disulfide bridges that are important to enzyme activity Fe = Iron = Site of catalytic reaction in many redox enzymes, essential for chlorophyll formation Mg = Magnesium = Involved in stabilization of ribosomes, cofactor for many enzymes, structural component of chlorophyll

Na = Sodium = Beneficial to Halophytes (Mangrove, Atriplex, etc) Cl = Chlorine = Involved in photolysis of water in photosynthesis Cu = Copper = site of catalytic reaction for some enzymes Mn = Manganese = Respiratory enzyme cofactor, involved in photolysis of water, required for auxin synthesis Co = Cobalt = Structural component of vitamin B12, necessary for nitrogen fixation Zn = Zinc = Involved in auxin synthesis, enzyme cofactor Mo = Molybdemun = Involved in reduction of nitrates B = Boron = Involved in translocation and absorption of sugar, interacts with Ca flux Structual Cofactors, osmotic relationships

Essential elements in plants

Symptoms of Mineral Deficiency The symptoms of mineral deficiency – Depend partly on the nutrient’s function – Depend on the mobility of a nutrient within the plant Deficiency of a mobile nutrient – Usually affects older organs more than young ones Deficiency of a less mobile nutrient – Usually affects younger organs more than older ones

The most common deficiencies – Are those of nitrogen, potassium, and phosphorus Phosphate-deficient Healthy Potassium-deficient Nitrogen-deficient

Soil quality is a major determinant of plant distribution and growth Along with climate – The major factors determining whether particular plants can grow well in a certain location are the texture and composition of the soil Texture – Is the soil’s general structure Composition – Refers to the soil’s organic and inorganic chemical components

Texture and Composition of Soils Various sizes of particles derived from the breakdown of rock are found in soil – Along with organic material (humus) in various stages of decomposition The eventual result of this activity is topsoil – A mixture of particles of rock and organic material

The topsoil and other distinct soil layers, or horizons – Are often visible in vertical profile where there is a road cut or deep hole Figure 37.5 The A horizon is the topsoil, a mixture of broken-down rock of various textures, living organisms, and decaying organic matter. The B horizon contains much less organic matter than the A horizon and is less weathered. The C horizon, composed mainly of partially broken-down rock, serves as the “parent” material for the upper layers of soil. A B C

Soils in the Miamian series, for example, are well drained. They typically have a very dark grayish brown to brown silt loam or loam topsoil layer ("A horizon") 5 to 10 inches thick. They commonly have a brown or yellowish brown subsoil layer ("B horizon"), 8 to 35 inches thick, with a higher clay content than the A horizon. Below the subsoil, soils in the Miamian series have a brown to light olive brown substratum ("C horizon") that is slightly or moderately alkaline and has a lower clay content than the B horizon.

After a heavy rainfall, water drains away from the larger spaces of soil – But smaller spaces retain water because of its attraction to surfaces of clay and other particles The film of loosely bound water – Is usually available to plants (a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root. Soil particle surrounded by film of water Root hair Water available to plant Air space

Acids derived from roots contribute to a plant’s uptake of minerals – When H + displaces mineral cations from clay particles (b) Cation exchange in soil. Hydrogen ions (H + ) help make nutrients available by displacing positively charged minerals (cations such as Ca 2+ ) that were bound tightly to the surface of negatively charged soil particles. Plants contribute H + by secreting it from root hairs and also by cellular respiration, which releases CO 2 into the soil solution, where it reacts with H 2 O to form carbonic acid (H 2 CO 3 ). Dissociation of this acid adds H + to the soil solution. H 2 O + CO 2 H 2 CO 3 HCO 3 – + Root hair K+K+ Cu 2+ Ca 2+ Mg 2+ K+K+ K+K+ H+H+ H+H+ Soil particle – – – – – – – – –

Soil Conservation and Sustainable Agriculture In contrast to natural ecosystems – Agriculture depletes the mineral content of the soil, taxes water reserves, and encourages erosion The goal of soil conservation strategies – Is to minimize this damage

Fertilizers Commercially produced fertilizers – Contain minerals that are either mined or prepared by industrial processes “Organic” fertilizers – Are composed of manure, fishmeal, or compost

International Fertilizer Industry Association All fertilizer labels have three bold numbers. The first number is the amount of nitrogen (N), the second number is the amount of phosphate (P2O5) and the third number is the amount of potash (K2O). These three numbers represent the primary nutrients (nitrogen(N) - phosphorus(P) - potassium(K)).primary nutrientsnitrogen phosphoruspotassium This label, known as the fertilizer grade, is a national standard. A bag of fertilizer contains 10 percent nitrogen, 10 percent phosphate and 10 percent potash. A Homeowner's Guide to Fertilizer

Hypoxia means an absence of oxygen reaching living tissues. In coastal waters, it is characterized by low levels of dissolved oxygen, so that not enough oxygen is available to support fish and other aquatic species. Nutrients, such as nitrogen and phosphorous, are essential for healthy marine and freshwater environments. However, an over overabundance of nutrients can trigger excessive algal growth (or eutrophication) which results in reduced sunlight, loss of aquatic habitat, and a decrease in oxygen dissolved in the water. Excess nutrients may come from a wide range of sources: Runoff from developed land Atmospheric deposition Soil erosion Agricultural fertilizers Sewage and industrial discharges also contribute nutrients. Recent estimates indicate 70% of all Nitrogen within Nitrogen Cycle on Earth is currently contributed by human activity! Death in the Gulf

Nitrogen is often the mineral that has the greatest effect on plant growth Plants require nitrogen as a component of – Proteins, nucleic acids, chlorophyll, and other important organic molecules

Soil Bacteria and Nitrogen Availability Nitrogen-fixing bacteria convert atmospheric N 2 – To nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis Atmosphere N2N2 Soil N2N2 N2N2 Nitrogen-fixing bacteria Organic material (humus) NH 3 (ammonia) NH 4 + (ammonium) H + (From soil) NO 3 – (nitrate) Nitrifying bacteria Denitrifying bacteria Root NH 4 + Soil Atmosphere Nitrate and nitrogenous organic compounds exported in xylem to shoot system Ammonifying bacteria

Plant nutritional adaptations often involve relationships with other organisms Two types of relationships plants have with other organisms are mutualistic – Symbiotic nitrogen fixation – Mycorrhizae

The Role of Bacteria in Symbiotic Nitrogen Fixation Symbiotic relationships with nitrogen-fixing bacteria – Provide some plant species with a built-in source of fixed nitrogen From an agricultural standpoint – The most important and efficient symbioses between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)

Along a legumes possessive roots are swellings called nodules – Composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria (a) Pea plant root. The bumps on this pea plant root are nodules containing Rhizobium bacteria. The bacteria fix nitrogen and obtain photosynthetic products supplied by the plant. Nodules Roots

The bacteria of a nodule – Obtain sugar from the plant and supply the plant with fixed nitrogen Each legume – Is associated with a particular strain of Rhizobium

Development of a soybean root nodule Infection thread Rhizobium bacteria Dividing cells in root cortex Bacteroid 2 The bacteria penetrate the cortex within the Infection thread. Cells of the cortex and pericycle begin dividing, and vesicles containing the bacteria bud into cortical cells from the branching infection thread. This process results in the formation of bacteroids. Bacteroid Developing root nodule Dividing cells in pericycle Infected root hair Nodule vascular tissue 4 3 Growth continues in the affected regions of the cortex and pericycle, and these two masses of dividing cells fuse, forming the nodule. Roots emit chemical signals that attract Rhizobium bacteria. The bacteria then emit signals that stimulate root hairs to elongate and to form an infection thread by an invagination of the plasma membrane. 1 4 The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant.

The Molecular Biology of Root Nodule Formation The development of a nitrogen-fixing root nodule – Depends on chemical dialogue between Rhizobium bacteria and root cells of their specific plant hosts

Symbiotic Nitrogen Fixation and Agriculture The agriculture benefits of symbiotic nitrogen fixation – Underlie crop rotation In this practice – A non-legume such as maize is planted one year, and the following year a legume is planted to restore the concentration of nitrogen in the soil

Mycorrhizae and Plant Nutrition Mycorrhizae – Are modified roots consisting of mutualistic associations of fungi and roots The fungus – Benefits from a steady supply of sugar donated by the host plant In return, the fungus – Increases the surface area of water uptake and mineral absorption and supplies water and minerals to the host plant

The Two Main Types of Mycorrhizae In ectomycorrhizae – The mycelium of the fungus forms a dense sheath over the surface of the root aEctomycorrhizae. The mantle of the fungal mycelium ensheathes the root. Fungal hyphae extend from the mantle into the soil, absorbing water and minerals, especially phosphate. Hyphae also extend into the extracellular spaces of the root cortex, providing extensive surface area for nutrient exchange between the fungus and its host plant. Mantle (fungal sheath) Epidermis Cortex Mantle (fungal sheath) Endodermis Fungal hyphae between cortical cells (colorized SEM) 100  m (a)

In endomycorrhizae – Microscopic fungal hyphae extend into the root Epidermis Cortex Fungal hyphae Root hair 10  m (LM, stained specimen) Cortical cells Endodermis Vesicle Casparian strip Arbuscules 2 Endomycorrhizae. No mantle forms around the root, but microscopic fungal hyphae extend into the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae that form arbuscules, providing an enormous surface area for nutrient swapping. The hyphae penetrate the cell walls, but not the plasma membranes, of cells within the cortex. (b) Farmers and foresters – Often inoculate seeds with spores of mycorrhizal fungi to promote the formation of mycorrhizae

Staghorn fern, an epiphyte EPIPHYTES PARASITIC PLANTS CARNIVOROUS PLANTS Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite Host’s phloem Haustoria Indian pipe, a nonphotosynthetic parasite Venus’ flytrap Pitcher plants Sundews Dodder Epiphytes, Parasitic Plants, and Carnivorous Plants Some plants Have nutritional adaptations that use other organisms in nonmutualistic ways