Topic 14.2 - Plant Nutrition

Biology 1001 - 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 Ca2+, Mg2+, K+

Generally function as components of macromolecules eg. Mg2+ 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 Mg2+ 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