1. Plant Nutrition

2. How plants acquire and use mineral nutrients
Mineral Nutrition
How plants acquire and use mineral nutrients
1. Why is mineral nutrition important?
2. What are the essential mineral nutrients?
classification systems
3. Mineral nutrients in the soil
nutrient availability
adsorption to soil particles
effects of pH
4. Roots and mineral nutrient acquisition
root structure
depletion zones
4. Mycorrhizae
5. Nitrogen - the most limiting soil nutrient

3. Why is mineral nutrition important?
2. In most natural soils, the availability of mineral nutrients limits plant growth and primary productivity.
Nutrient limitation is an important selective pressure and plants exhibit many special traits related to the need to acquire and use mineral nutrients efficiently.

4. 2. What are the essential mineral nutrients?
Macronutrients - present in relatively high concentrations in plant tissues.
N, K, P, Ca, Mg,S, Si
Nitrogen is most commonly limiting to productivity of natural and managed soils. Phosphorus is next most limiting, and is most limiting in some tropical soils.
Micronutrients - present in very low concentrations in plant tissues.

5. There are 17 essential elements required for plant growth
What defines an “essential” element?
In its absence the plant cannot complete a normal life cycle
The element is part of an essential molecule (macromolecule, metabolite) inside the plant
Most elements fall into both categories above (e.g., structural vs. enzyme cofactor)
These 17 elements are classified as
9 macronutrients (present at > 10 mmol / kg dry wt.)
8 micronutrients (< 10 mmol / kg dry wt.)

6. All mineral nutrients together make up less than 4% of plant mass,
yet plant growth is very sensitive to nutrient deficiency.
Not considered mineral nutrients
PP05T011.jpg

7. Micronutrients are present in very low concentrations
ppm
Very low concentrations, but still essential
because of specialized roles in metabolism
PP05T012.jpg

8. PP05T040.jpg

9. I. Plant Nutrients C. Macro/Micronutrients
Hydroponics allowed us to see what was needed
The necessary nutrients are those the plant can not grow with out
Come in two categories
1. Macronutrients (C, O, H, N, S, P, K, Ca, Mg)
Majority of the time used for the main organic compounds
2. Micronutrients (Cl, Fe, B, Mn, Zn, Cu, Mo, Ni)
Mostly cofactors for particular enzymes (Fe -> Cytochromes

10. Hydroponic culture techniques come in different flavors
Fig. 12.1
Main disadvantage of simple solution culture → as plant grows, it selectively depletes certain minerals
When one becomes limiting, growth will slow significantly
Can grow in vermiculite/perlite (inert, non-nutritive) and refertilize daily
Commercially, it is often cheaper and easier to continuously bathe roots in a nutrient solution (nutrient film technique)
Aerates
Standard nutrient level maintained
Continuous process monitoring
To define “essential”, researchers need inert materials contributing low levels of nutrients (NO METAL PARTS!)
Fig. 12.2

12. Soils particles are generally negatively charged and so bind
positively charged nutrient ions (cations).
Cation Exchange Capacity refers to a soil’s ability to bind cations.
PP05050.jpg
NH4+, NO3-, Cl-, PO4-2, SO4-2

13. Soil pH influences availability of soil nutrients.
PP05040.jpg

14. Roots
Provide large surface area for nutrient uptake
- Root hairs

15. Root hairs

16. Depletion zones - regions of lower nutrient concentration -develop
around roots
PP05070.jpg
Fig. 5.7

17. 17 17

18. Root hairs
Root hairs

19. 4. Roots and mineral nutrient acquisition
Fine roots and root hairs “mine” the soil for nutrients.
Mycorrhizal hyphae do this even better.

20. K+ K+ K+
Clay
particle H+ K+ K+ K+ K+ K+
Root hair

21. Vesicular Arbuscular Mycorrhiza
Inside root
Intercellular mycelium
Intracellular arbuscule
tree-like haustorium
Vesicle with reserves
Outside root
Spores (multinucleate)
Hyphae
thick runners
filamentous hyphae
Form extensive network of hyphae
even connecting different plants

22. Mycorrhizae
Ectotrophic mycorhizae

24. Why mycorrhiza?
Roots and root hairs cannot enter the smallest pores

25. Nitrogen fixing bacteria
Genus: Rhizobium
N NH4
Supply of electrons

26. Ion uptake

27. Active uptake Proton pumps establish an electrochemical gradient. Net
Outside cell (positive)
Net
positive charge
Net negative
charge
Inside cell (negative)

28. Cations enter root hairs via channels or carriers

29. Anions enter root hairs via cotransporters.

30. Concept of critical concentration illustrated
Above critical concentration, there is no net benefit (e.g., yield increase) if more nutrient is supplied
Below critical concentration, nutrient level limits growth!
Not shown on diagram: all elements eventually become toxic at very high concentrations

31. Analysis of plant tissues reveals mineral deficiencies

32. The absence of essential elements causes deficiency symptoms
Essential because of their metabolic functions
Characteristic deficiency symptoms shown because of these roles
Typical deficiency responses are
Chlorosis: yellowing; precursor to
Necrosis: tissue death
Expressed when a supply of an essential metabolite becomes limiting in the environment
Element concentrations are limiting for growth when they are below the critical concentraion
This is the concentration of nutrient in the tissue just below the level giving maximum growth

33. Limiting nutrient levels negatively affect growth
Plant responses to limiting nutrients usually very visible: affects yield/growth!
Again, chlorosis and necrosis of leaves is typical
Sometimes straightforward relationship
e.g., in chlorosis (lack of green color),
N: chlorophyll component
Mg: cofactor in chlorophyll synthesis
Ctrl
- P
- N
- Fe
- Ca

34. Chlorosis

35. Necrosis

36. Stunted growth