1. §3 Plant Absorption of Mineral Nutrition

2. 3.1 Characteristics of Mineral Absorption
1. Root tips (root hair zone) is the main area for mineral absorption.

3. (2)absorption of minerals promotes water absorption. Difference:
2. Relative independence for water and mineral absorption
Dependence:
(1)minerals must be dissolved in water for absorption and transportation;
(2)absorption of minerals promotes water absorption.
Difference:
(1) the rate is different;
(2) the mechanism is different: water is absorbed by osmosis while mineral is absorbed mainly by active transport.

4. 3. selective absorption of ions.
1). Different uptake of various ions in the same solution

5. 2). The plants can also selectively absorb different ions in a certain salt leading to alteration of soil pH.
e.g: for NaNO3: prefers NO3-, so more OH- or HCO3- from root surface into soil solution, soil pH increase, NaNO3 is called physiologically alkaline salt.
for (NH4)2SO4: prefers NH4+, so more H+ from root surface into soil solution, soil pH decrease, (NH4)2SO4 is called physiologically acid salt.
But forNH4NO3: uptake of NH4+ and NO3- was somewhat equal, so soil pH does not change at all, NH4NO3 is called physiologically acid neutral salt. .

6. Exchangeable adsorption
3) How does this happen?
Exchangeable adsorption H+ H＋
HCO3－
＋ NaNO3
NO3－

7. A. NaCl+KCl+CaCl2；B. NaCl+CaCl2
小麦根在盐类溶液中的生长情况
A. NaCl+KCl+CaCl2；B. NaCl+CaCl2
C. CaCl2； D. NaCl
4. Toxicity of single salt(单盐毒害）
single salt results in plant poisoning is called toxicity of single salt.
5. Ion antagonism（离子拮抗）
Ion antagonism is referred to as the interaction among ions can limit toxicity of single salt.

8. 6. Balanced solution（平衡溶液）
Solution containing many salts with optimal concentration can not only provide the plants with essential nutrition but also avoid ionic toxicity.
E.g. Hoagland nutrient solution; soil solution

9. 3.2 Ion Transport in Roots
Ions Moving through the Root Cross Both Symplastic and Apoplastic Spaces
Xylem Parenchyma Cells Participate in Xylem Loading

10. Ion Symplast Apoplast Symplast Apoplast Figure 5.11
Root epidermis (rhizodermis), cortical cells
Endodermis + suberized Casparian band
Vascular tissues: vessel elements, parenchyma cells
Ion
Symplast
Apoplast
Symplast
Apoplast

11. The other function of Casparian band
Because the ion concentration of stelar apoplast is much higher than in the surrounding cortex, the other function of Casparian band could be to prevent loss of ions from the stele by diffusion.
In addition, it suggests that ion release into the vessels is a different kind of process than ion uptake by the roots and possibly by ion loading.

12. 3.3 Factors influencing mineral absorption
Temperature:
High temp: enzyme denaturizing, root early aging.
Low temp: metabolism reduction, high viscosity, low microbe activity, low decomposition.

13. 2: O2 Absorption increases when [O2] is between 1-4%,
then keeps steady when [O2] is over 4%
Soil [O2] is between 10.35~20.7%.
O2 insufficient occurs only when flooding and soil case-hardening happens.

14. 3: nutrient concentration.

15. 4: soil pH Alkaline soil: lack of Fe, Ca,Mg,Cu,Zn for low solubility
Acidic soil: PO4,K,Ca,Mg :easily leached away for high solubility
Fe,Mn,Al: toxic for high solubility

16. 5. Soil Colloids
Colloids are particles small enough to remain in suspension but too large to go into true solution.
Colloids provide (1) large specific surface area binding surface for cations and (2) carry a large number of charges for ion exchange.

17. Colloids provide large specific surface area
Particles of colloidal dimension have a high surface area per unit mass, or specific surface area.
Specific surface area: loam>clay>silt>sand
So, nutrient reservoir capacity: loam>clay>silt>sand

18. Colloids provide binding surface for cations.
It’s colloidal clay (Al2Si2O5·(OH)4) or colloidal carbonaceous residue (humus) that the surfaces are all negatively charged, which makes soil colloids capable of binding cations and easily hydrated.

19. Because the ability of exchange cations of colloidal surfaces, the colloidal fraction of soil is the principal nutrient reservoir for the soil.

20. Protons (hydrogen ion) can replace most of the cations easily
Protons (hydrogen ion) can replace most of the cations easily. Therefore, plant roots also secrete protons to make cations available for absorption. Acid rain will wash out the cations of soil solutions and colloidal surfaces by the same mechanism of cation exchange.

21. Because soil is predominately negative charged, the anions tend to leach out of the soil. This is the reason of eutrophication.
Due to the inability of soil to hold anion, farmers usually apply at least twice the amount of nitrogen (NO3-) required on the crops. However, most of the nitrogen is leaching into the ground water, contaminating streams and lakes. High nitrogen content in the water bodies stimulate the growth of algae, resulting eutrophication.

22. Root-microbe interactions
7. Microorganisms
Root-microbe interactions
Bacteria
mucilages (mucigels: 黏胶层)
proteoid roots
Mycorrhiza
ectomycorrhizae
endomycorrhizae
VAM (vasicular-arbuscular mycorrhiza)

23. Because bacteria can enhance nutrient uptake of roots, the Golgi apparatus of root cells (root cap cells, young epidermis cells, and root hairs) secrete polysaccharide-based mucilages to attract bacteria.
Mucilages
Bacteria
Colloidal soil particles

24. Ectomycorrhizae
-this family of mycorrhizae is restricted to temperate trees and shrubs such as pines and beech.
-they are short, highly branched, and ensheathed by a tightly interwoven mantle of fungal hyphae.
-it also penetrates theintercellular of apoplastic spaces of the root cortex, forming a intercellular network

25. Endomycorrhizae
-it is found in some species of virtually every angiosperm family and most gymnosperms.
-it is developed extensively within cortical cells of the host roots.
-VAM (vesicular-arbuscular mycorrhiza) is the most common type of endomycorrhiza.
-VAM forms arbuscule with host cells without penetrating protoplasm of its host. Arbuscules increase increase contact surface area by two or three times.

26. Maize seedlings that is not colonized by myccorrhiza.
Figure 13.15

27. Nutrient depletion zone defines the limits of the soil from which the root is able to readily extract nutrient elements.
Mycorrhiza can extend the nutrient depletion zone for a plant.
Figure 13.16

28. 3.4 Foliar nutrition(叶片营养）
Foliar nutrition is a method by which the fertilizer is directly applied to leaves.
Advantage:
① rapid
② efficiency
③ effective replenish during the early and late stages of plant life.

29. Attention：
①not too high concentration, macroelements ~ 1%, microelements ~ 0.1%.
②mixture of nutrition solution and detergent (e.g. triton,tween).
③applied in the evening or cloudy day but not just before raining.

30. § 4 Transport and allocation of minerals in plant
Points:
Transport: forms, pathway and velocity.
Allocation: prefers to growing tissues or organs; removable elements remove to the growing or deficient tissues.

31. 4.1 Transport of minerals in the plant
Method: isotope tracing
Pattern: N：mostly as amino acids (mainly Asp and a little Ala, Met, Val) and amides (Asn and Gln); P: mainly as PO43-; S: mainly as SO42-，metals: as ions.
Pathway: For the nutrients absorbed by root: upward through xylem trachea or transpiration stream. For the nutrients absorbed by leaf: downward through phloem sieve tubes. N.B. They can also move by Cross transport between xylem and phloem slightly.
Velocity: cm/h

32. 4.2 Allocation of minerals
Mobile elements: K，N，P，Mg，Zn are mostly distributed in active organs, while immobile elements such as S，Ca，Fe，Mn and B are distributed mainly in non-active organs.
During reproductive growth, mobile elements will be transported to flowers and fruits.
Before leaf abscission, mobile elements will be transported to the stem and root.

34. Deficiencies of phloem-mobile nutrients show up in the old leaves first.
Deficiencies of phloem-immobile nutrients show up in young leaves first.

35. § 5 Physiological basis for reasonable fertilization
5.1 Why fertilizer?
Increase photosynthesis by increasing leaf area, chlorophyll content, leaf longevity, ameliorate the allocation of photosynthetic products to increase harvest index.
Regulate growth and development:
N: promotes the growth of leaves
P K: promotes the transport of photosynthetic products to the sinks
Ameliorate soil conditions such as soil structure, temp, pH and microbes.

36. 5.2 Rules of fertilization
Different crops need different nutrients
Crops need different nutrients at different stages
Crops need different amount of nutrients at different stages.
Germination: No need
Seedling: high
Flowering and fruiting: high
Senescence: Low
Critical period of nutrition: A period during which plant is most sensitive to nutrition deficiency and most easily get injured .

37. 5.3 Diagnosis of nutrition deficiency
Morphological indices:
Leaf color;
leaf growth rate;
leaf appearance
Physiological indices
Element concentration
Amides concentration
Enzyme activity