1. HORT 301 – Plant Physiology October 5, 2007
Mineral Nutrition
HORT 301 – Plant Physiology
October 5, 2007
Taiz and Zeiger, Chapter 5, Web Topics 5.1 and 5.2
courtesy of Burkhard Schulz

2. Mineral nutrition – acquisition and utilization by plants of naturally occurring essential mineral elements
Plant nutrient status – based on symptoms (growth, pigmentation, senescence, etc.), and soil and tissue analyses
Mineral nutrient acquisition from the soil – chemical forms and availability of mineral nutrients in the soil solution
Mineral nutrient absorption by roots – uptake from the soil
Mycorrhizal fungi and mineral nutrient absorption by plants – symbiosis that facilitates absorption

3. Mineral nutrition – acquisition and use of essential mineral nutrients by plants
Naturally occurring minerals (elemental, or simplest chemical or molecular form) that are in soils
Plants access mineral nutrients typically by root absorption from the soil solution
Mineral nutrients are products of recycling of organic matter and soil weathering
Mineral nutrients often limit plant growth, agricultural practice is to optimize the nutrient status of a plant by soil amendment

4. Essential elements – mineral nutrients that are required by plants for metabolic function, and growth and development
These nutrients together with CO2 and H2O, and sunlight (light energy) allow plants to synthesize all other necessary molecules
An essential mineral nutrient is:
a required component of structure (silicon in the cell wall) or plant
metabolism
2. necessary for plant growth, development or reproduction

5. Hydroponics (liquid solution culture) - facilitated determination of essential mineral nutrients
Some micronutrients are required in low amounts, essentiality was difficult to establish using soil
Solution culture requires a synthetic “medium” containing essential nutrients, e.g.Hoagland’s solution

6. Essential elements are categorized as macronutrients or micronutrients based on relative concentration in plant tissue (dry weight)
Macronutrient – up to 1.5%, 15,000 ppm in dry matter

7. Micronutrient - 100 ppm (dry matter) or less

8. Classification of essential mineral nutrients by function
Group 1 (N and S) – components of organic molecules
Group 2 (P, Si, B) – energy storage or cellular structure

9. Group 3 (K, Ca, Mg, Cl, Mn, Na) – present as ions in cells, enzyme co-factors, osmotic adjustment, signaling

10. Group 4 (Fe, Zn, Cu, Ni, Mo) – metals involved in redox reactions (electron transfer),

11. Nutrient deficiency symptoms – soils (generally) have a limited mineral nutrient load capacity
Plant nutrient deficiency symptoms may be used to determine when and what type of soil nutrient amendment (fertilization) is necessary
Symptoms are complex, occurring from deficiency of different individual nutrients and further complicated by stresses, see Web Topic 5.1 for an in-depth treatise of plant nutrient deficiency symptoms

12. Nutrient Deficiency Symptoms

13. Nutrient deficiency symptoms – soils (generally) have a limited mineral nutrient load capacity
Plant nutrient deficiency symptoms may be used to determine when and what type of soil nutrient amendment (fertilization) is necessary
Symptoms are complex, occurring from deficiency of different individual nutrients and further complicated by stresses, see Web Topic 5.1 for an in-depth treatise of plant nutrient deficiency symptoms
Plant tissue analysis – a precise method to assesses nutrient status of tissues, used to optimize fertilizer application (crop production + reduced pollution)

14. HORT 301 – Plant Physiology October 5, 2007
Mineral Nutrition
HORT 301 – Plant Physiology
October 5, 2007
Taiz and Zeiger, Chapter 5, Web Topics 5.1 and 5.2
courtesy of Burkhard Schulz

15. Mineral nutrition – acquisition and utilization by plants of naturally occurring essential mineral elements
Plant nutrient status – based on symptoms (growth, pigmentation, senescence, etc.), and soil and tissue analyses
Mineral nutrient acquisition from the soil – chemical forms and availability of mineral nutrients in the soil solution
Mineral nutrient absorption by roots – uptake from the soil
Mycorrhizal fungi and mineral nutrient absorption by plants – symbiosis that facilitates absorption

16. Tissue mineral nutrient content zones for plant growth:
Critical concentration - minimum tissue nutrient content for maximum growth or yield
Toxic concentration zone – content at which yield declines because the nutrient is in excess
Adequate zone - determination of adequate zones minimizes fertilization inputs

17. Mobile nutrients (N, K, Mg, P, Cl, Na, Zn and Mo) - symptoms are evident first in older leaves
Immobile nutrients (Ca, S, Fe, B and Cu) - symptoms develop first in the younger leaves

18. Nutrient Deficiency Symptoms

19. Mineral nutrient acquisition from the soil - plants access virtually all mineral nutrients from the soil solution
Mineral nutrients – derived from inorganic as well as organic components of the soil rhizosphere
Organic decomposition (microbes) “releases” mineral nutrients to the soil solution (mineralization)

20. Mineral nutrient forms
Macronutrients
Micronutrients

21. Soil particles – both inorganic (gravel (>2 mm) to clay (< 2 µm)) and organic soil particles have a negative charge
Cation exchange capacity (CEC) - negatively charged soil particles form electrostatic interactions with cationic mineral nutrients (positively charged ions)
CEC facilitates availability of cations (positively charged elements or molecules) for absorption by plant roots

22. Negatively charged ions (anions), e. g
Negatively charged ions (anions), e.g., NO3-, H2PO4-, Cl- - remain in the soil solution between particle spaces, adhesion of water
Limited anion exchange capacity of soils - anions form bridges with multivalent cations like Fe2+or Al3+ and H2PO2-
OR, anions are present in relatively insoluble compounds e.g., SO42- in gypsum (CaSO4), which are gradually released
Anions are repelled by surface particle charge and tend to be leached through the soil to the ground water

23. Decomposition of organic material lowers the pH
pH and mineralization – affect mineral nutrient availability in soil solution, pH 5.5 to 6.5 is optimal
Decomposition of organic material lowers the pH
Soil amendments alter pH - lime (CaO, CaCO3, Ca(OH)2, attract protons) increases pH (alkaline)
Sulfur reduces pH (mineralization results in release of sulfate and hydrogen ions) of the soil solution
Shaded area is the relative nutrient availability to plants

24. Nutrients move in the soil solution to the root surface by pressure-driven bulk flow and diffusion, directly linked to water flow

25. Root structure and mineral nutrient absorption – roots acquire water and mineral nutrients
As with water, root surface area and absorption is enhanced substantially by production of secondary roots and root hairs

26. Roots seek water and nutrients, e.g. water - hydrotropism

27. Effect of Localized Supply of PO4,2- , NO3- , NH4+ , and K+ on Root Growth in Barley
Part of the root system receiving the complete nutrient solution
Part of the root system receiving the nutrient solution deficient
in specified nutrient -
Drew (1975) New Phytol. 75 :

28. Main regions of a primary root are the meristematic zone, elongation and maturation zones
Meristematic – root cap protects the root, gravitropic (gravity response), perhaps other tropic/trophic responses, quiescent zone of meristem initials and cell division for proliferation of cell types
Elongation zone (0.7 to 1.5 mm from apex) – reduced cell division, rapid cellular elongation and development of cell types, including endodermis with Casparian strip, xylem and phloem

29. Maturation zone – root hair zone that increases the surface area for absorption of water and mineral nutrients
Foliar application facilitates more rapid uptake of mobile elements

30. Mycorrhizal fungi facilitate water and mineral nutrient uptake into roots – extend the root absorption surface area
Mycorrhiza fungi – symbiotic (sugar for mineral nutrients) association between a fungus and plant roots, 83% of dicot species, 79% of monocots and all gymnosperms
Ectomorphic mycorrhizal fungi – hyphae extend into the cortex (apoplast) of plants and into the soil, up to 100% increase in surface area for nutrient absorption, reduces the nutrient depletion zone at the root surface

31. Vesicular arbuscular mycorrhizal fungi – hyphae are less dense and penetrate into cortical cells where they branch (arbuscule) and transfer nutrients to the plant root, hypae extend from the root facilitating nutrient acquisition beyond the root surface
It is not known precisely how nutrients move from the hyphae to the plant cells, i.e. diffusion or release at hyphal death