Chapter 37 Plant Nutrition

Uptake of nutrients in plants: Leave and roots

I.Nutrients A.Essential: required for the plant to grow & life cycle B.Macronutrients- required in large amounts. Ex. carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium C.Micronutrients- required in small amounts; cofactors of enzyme action. Ex. chlorine, iron, boron, manganese, zinc, copper, molybdenum, nickel

D.Deficiency chlorosis (lack of magnesium; chlorophyll production) E.Dry weight of plant = 95% organic, 5% inorganic

II.Soil A.Determines plant growth & variety (also climate) B.Soil horizons: Loams: The most fertile topsoil

B. Soil Horizons: O, A, E, B, C, R O Horizon - The top, organic layer of soil, made up mostly of leaf litter and humus (decomposed organic matter). A Horizon - The layer called topsoil; Seeds germinate and plant roots grow in this dark- colored layer. It is made up of humus (decomposed organic matter) mixed with mineral particles. E Horizon - This eluviation (leaching) layer is light in color; It is made up mostly of sand and silt, losing most of its minerals and clay as water drips through the soil (in the process of eluviation).

B Horizon - Also called the subsoil - It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above. C Horizon - Also called regolith: It consists of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very little organic material is found in this layer. R Horizon - The unweathered rock (bedrock) layer that is beneath all the other layers. e/strahler/ /animations/ch21_animations/an imation1.html

III.Nitrogen Fixation A.The atmosphere is ~80% N 2. Plants need nitrogen but cannot take nitrogen gas directly out of the atmosphere. 1.Nitrogen must be converted to ammonium (NH 4 + ) or nitrate (NO 3 - ) to be absorbed by plants. 2.Some nitrogen is put into the soil when dead organisms decompose in the soil.  Microbes break down dead organisms  However, some denitrifying bacteria will convert NO 3 - to N 2.

B.Nitrogen-fixing bacteria: bacteria that take N 2 from the atmosphere and convert it into NH 4 + and NO Nitrifying bacteria: convert NH 4 + to NO Ammonifying bacteria: convert dead organic material into NH 4 +.

THE NITROGEN CYCLE:

IV.Plant symbiosis, I A.Rhizobium bacteria (found in root nodules in the legume family) B.Mutualistic: legume receives fixed N 2  bacteria receives carbohydrates & organic materials

1.Roots emit chemical signals that attract Rhizobium. The bacteria then emit signals that elongate root hairs and form an invagination (infected thread).

2.Bacteria penetrate the root cortex. Root cells divide, and contain vesicles with bacteria in them. 3.Growth continues in the cortex and pericycle. The two masses fuse forming the nodule.

4.The nodules continue to grow into the vascular tissue, which supplies nutrients to the nodules.

Nodules

V.Plant symbiosis, II A.Mycorrhizae (fungi) modified roots B.Mutualistic: fungus receives sugar  plant receives increased root surface area and increased phosphate uptake

C. Two types: ectomycorrhizae ensheaths the root, woody plants, trees, pines endomycorrhizae (90% of plants) through cell wall but not cell membrane (arbuscles)

Fungal Hyphae in between plant root cells of ectomycorrhizae Fungal hyphae branch into the root cells, but do not penetrate the plasma membrane; arbuscles

VI.Plant parasitism & predation A.Mistletoe (parasite)- use haustoria to siphon xylem sap from host tree B.Epiphytes- autotrophic plant that nourishes itself but grows on the surface of another plant, usually on the branches or trunks of trees (mosses) C.Carnivorous plants- glands secrete digestive juices

Mistletoe