1. Chapter 37
Plant Nutrition

2. I. Nutritional Needs of Plants

3. 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

4. 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

7. II. Soil

8. 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

10. 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?

12. 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

13. 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

14. 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

15. 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+

17. IV. Symbiosis of Plants and Soil Microbes

18. 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

20. 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

22. 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

24. 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

25. 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

27. 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

29. 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

30. Sun Dew Plant