Topic Plant Nutrition Biology November 18, 2005

5. Essential Minerals of Plants Mineral nutrients are essential chemical elements that plants extract from the soil in the form of inorganic ions Macronutrients are needed in relatively large amounts  Nitrates supply nitrogen  Phosphates supply phosphorus  Sulfates supply sulfur  Ca 2+, Mg 2+, K +  Generally function as components of macromolecules eg. Mg 2+ is a component of chlorophyll; K + functions in water balance Micronutrients are needed in very small amounts  Ionic forms of chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum  Often function as enzyme cofactors, components, or to activate enzymes Macronutrients and micronutrients are essential elements because they are required for a plant to complete its life cycle  Without the proper nutrients, mineral deficiencies occur

Mineral Deficiencies Chlorosis due to Mg 2+ deficiency

6. Obtaining Nutrients  Figure 37.2!  Carbon dioxide enters the plant through the stomata in the leaf  Water, mineral nutrients and oxygen are absorbed through the roots  Water and oxygen exit the plant through the leaf, while carbon dioxide is expelled from the roots  Plants are net producers of oxygen and net consumers of carbon dioxide and water 80-90% of a plant’s wet weight is water The bulk of a plant’s dry mass is derived from carbon dioxide

The Role of Bacteria in Symbiotic Nitrogen Fixation  Symbiotic relationships with nitrogen-fixing bacteria provide certain plants with a source of fixed nitrogen Usually plants in the legume family eg. Peas, soybeans, peanuts, alfalfa and clover The bacteria, such as Rhizobium, live in swellings on the roots called nodules that consist of plant cells with the bacteria in the form of bacteroids located in vesicles

Mycorrhizae and Plant Nutrition  Mycorrhizae (“fungus roots”) 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 The fungus increases the surface area for water uptake by the root, and selectively abosrbs phosphates and other minerals from the soil and supplies them to the plant Occur in most plant species, and probably represent an early adaptation to a terrestrial environment

Unusual Nutritional Adaptations of Plants  Epiphytes, parasitic plants and carnivorous plants use other organisms in unusual nonmutualistic ways Epiphytes nourish themselves but grow on other plants  They obtain water and minerals through leaves, from rain Parasitic plants absorb sugars and minerals from their hosts  Some are photosynthetic, some not  Roots may function as haustoria, nutrient-absorbing projections into the host plant Carnivorous plants obtain nitrogen and minerals by killing and digesting small animals such as insects  They are photosynthetic, but live in acid bogs and other mineral- poor soils

Unusual Nutritional Adaptations in Plants