Plant Nutrition (ch37) For a typical plant water and minerals come from the soil, while carbon dioxide comes from the air Branching roots and shoots of a vascular plant ensure procuring these raw materials for photosynthesis

Plants derive most of their organic mass from the CO2 of air they also depend on soil nutrients such as water and minerals CO2, source of C; through stomata. stomata, expels H2O and O2. H2O O2 CO2 H2O and minerals Minerals

SOIL – must be rich in minerals and sufficient H2O 37.2: Soil quality is a major determinant of plant distribution and growth, along with climate Soil Texture Is the soil’s general structure Composition Refers to the soil’s organic and inorganic chemical components

Many types of soil: Clay, silt, sandy, salty Loam is a type of soil with equal parts of sand, silt, and clay topsoil : a mixture of particles of rock and organic material

water drains rapidly from the larger spaces of soil Loam is a type of soil with equal amounts of sand, silt, and clay topsoil is a mixture of these sized particles of rock and organic material water drains rapidly from the larger spaces of soil But clings to surfaces of clay and org. particles

Soil pH determines availability of minerals to plants Acids derived from roots contribute to a plant’s uptake of minerals The H+ produced releases mineral cations from soil particles (esp clay) H2O + CO2 H2CO3 HCO3– + Root hair K+ Cu2+ Ca2+ Mg2+ H+ Soil particle –

Human Agriculture: Erosion, Irrigation, etc Topsoil from thousands of acres of farmland is lost to erosion each year in the United States Irrigation, & changes the chemical makeup of soil can make it saline lost to salinization, in millions of acres:

Soil Bacteria and Nitrogen Availability Nitrogen-fixing bacteria convert atmospheric N2 To nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis Nitrogenase is the enzyme used to catalyze the nitrogen fixation reaction Figure 37.9 Atmosphere N2 Soil Nitrogen-fixing bacteria Organic material (humus) NH3 (ammonia) NH4+ (ammonium) H+ (From soil) NO3– (nitrate) Nitrifying bacteria Denitrifying bacteria Root NH4+ Nitrate and nitrogenous organic compounds exported in xylem to shoot system Ammonifying bacteria

Symbiosis feeds the plants that feeds us Legumes possess root nodules containing nitrogen-fixing Rhizobium bacteria Nodules Roots

Symbiotic Nitrogen Fixation and Agriculture nitrogen fixation is the Underlying reason for crop rotation Corn and soybeans may be rotated to improve the soil for the sake of the corn

Mycorrhizae and Plant Nutrition 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 through photosynthesis In return, the fungus Increases the surface area for uptake of water and minerals

The Two Main Types of Mycorrhizae In ectomycorrhizae The mycelium of the fungus forms a dense sheath over the root Mantle (fungal sheath) (colorized SEM) 100 m (a)

In endomycorrhizae Microscopic fungal hyphae extend into the cells of the root Epidermis Cortex Fungal hyphae Root hair 10 m (LM, stained specimen) Casparian strip (b)

Agricultural Importance of Mycorrhizae Farmers and foresters Often inoculate seeds with spores of mycorrhizal fungi to promote the formation of optimal root systems

Epiphytes, Parasitic Plants, and Carnivorous Plants Some plants Have nutritional adaptations that use other organisms in non-mutualistic ways Epiphytes are plants that nourish themselves but grow on other plants Parasitic plants absorb nutrients from host plants Carnivorous plants procure additional minerals and nitrogen by digesting insects