Chapter 37 Plant Nutrition

I. Nutritional Needs of Plants

A. Basics Jean Baptiste van Helmont determined it was water, not soil, that made plants grow Stephen Hales determined plants are nourished by air Most weight of a plant comes from atmospheric CO2

B. Essential Nutrients Things that are required for a plant to grow from a seed to a seed bearing adult Macronutrients – elements required in large amounts - C,H,O,P,N,S (organic) and K,Ca,Mg Micronutrients – elements needed in small amounts - Fe,Cl,Cu,Mn,Zn,Mo,B,Ni - Most of them are enzyme cofactors Older leaves are affected by malnutrition because young tissue has more pulling power Most common are deficiencies in N, K, P

II. Soil

A. Basics It comes from rock broken down by freezing, acids, and plants Topsoil – rock pieces, living organisms, and humus (partially decayed stuff) Loam – best soil / equal sand, silt, and clay - provides air spaces and surface area for minerals and water Roots absorb soil solution

B. Cation Exchange Clay holds cations because it is negatively charged H+ ions produced by root hairs replace minerals which are being held by the clay Why is the pH of the soil so important in cation exchange?

C. Fertilizer Usually rich in N,P,K / 20-20-20 Compost is better for fertilization but is slower / commercial fertilizer can be wasted away

D. Irrigation Unavailability of water is the most common limiter of plant growth Irrigation can cause salty land as water evaporates / land can become hypertonic

E. Erosion Erosion can be prevented by windbreaks, terracing, and by planting certain crops Some soils that are contaminated might be able to be helped with phytoremediation This is where certain plants can remove certain contaminates

III. Nitrogen It is the mineral element that most often limits growth Plants only absorb ammonium (NH4+) or nitrate (NO3-) / mainly comes from decomposition Nitrogen Fixing Bacteria change N2 to NH3 in the soil / all life on Earth depends on this / nitrogenase does this by using 16ATP for every N2 Nitrifying bacteria oxidize NH4+ into NO3- which plants absorb and change back to NH4+

IV. Symbiosis of Plants and Soil Microbes

A. Symbiotic Nitrogen Fixation Legumes have nodules which are swellings on roots where Rhizobium, a nitrogen fixing bacteria, is found Mutualistic relationship Crop rotation is important to replenish nitrogen / plow under legumes Azolla and rice

A. Symbiotic Nitrogen Fixation Nodule formation: 1. Roots emit signals to attract Rhizobium 2. Rhizobium emits a signal for plant to make an infected thread (root) and bacteria move in 3. Bacteria move to cortex (bacteroids) and divide with cells and pericycle of stele divides 4. Both masses fuse and become the nodule

A. Symbiotic Nitrogen Fixation Molecular Biology: 1. Root Signal (flavonoid) 2. Activates Nod D gene (transcription factor) in bacteria 3. Binds to Nod Box activating Nod Gene 4. Nod Enzyme made 5. Nod Factor Made (chitin like, mimics plant growth factor) 6. Triggers infection thread production on root

B. Mycorrhizae Modified roots consisting of an association of roots and fungus Mutualistic / help with water uptake Found in almost all plants Nodulin genes and mycorrhizae genes are very similar but mycorrhizae are much older There are two types of Mycorrhizae: 1. Ectomycorrhizae 2. Endomycorrhizae

1. Ectomycorrhizae Form a dense sheath or mantle over the surface of the roots Hyphae grow into the cortex but do not penetrate the root cells Thicker, shorter, and more branched No root hairs are formed Found in woody plants and trees

2. Endomycorrhizae No mantle Microscopic Hyphae extend inward through the cell wall, but do not pierce the plasma membrane Push inward and form knots called arbuscles 90% of plant species have these

V. Parasitism and Predation in Plants Parasites - mistletoe sticks haustoria into trees and sucks out xylem sap - indian pipe uses mycorrhizae of other plants to get it’s nutrients Predators - compensate for poor soils (nitrogen) - pitcher plants and venus flytraps

Sun Dew Plant