Plant Nutrition

SWES 316

Section H

What Do Plants Need to Grow?

• Van Helmont early 1600s– Grew a tree in 200# of soil for 5 years, gave it

only water. After 5 yrs, he accounted for all but 2 oz of soil. Conclusion: water is the only essential nutrient for plants.

• Boyle mid 1600s– Plants contain “salts, spirits, earth, and oil”,

which he thought were derived from water. Agreed with van Helmont.

What Do Plants Need to Grow?• John Woodward 1700

– Grew spearmint in water from different sources (e.g. fresh, sewage).

– Concluded that “earth”, not water, was the principal nutrient of vegetation.

• Jethro Tull 1700– Believed that roots “eat” soil.

• Justus von Liebig early 1800s– C in plants comes from atmosphere, H and

O come from water, other elements from soil.

What are Plants Made of?

Water90.0%

Dry Matter10.0%

WaterDry Matter

Plant Composition

C, H, O95.0%

"Mineral Elements"5.0%

C, H, O"Mineral Elements"

Dry Matter

Elements Found in Plants

• At least 50 chemical elements have been found in plants. However, most are not needed for plant growth.

• There are 17 chemical elements that are apparently required for all plants, and some more that are required for some plants.

• Plants are about 90% water and only 10% solids. Of the solids, only about 5-10% actually comes from the soil.

Essential Nutrient Elements

• An element is essential if it functions in some way in plant metabolism.

• Specifically, essential elements are those for which:– 1) it is impossible for the plant to complete its life

cycle without that element, – 2) a deficiency can only be solved by supplying

that element, and – 3) the element is directly involved in the nutrition of

the plant (and not in solving an environmental circumstance).

Essential Elements

• The above definition includes 17 elements required by all plants:

"Macronutrients": C, H, O, N, P, K, S, Ca, Mg

"Micronutrients": Fe, Mn, Zn, Cu, Mo, B, Cl, Ni

Additional: Na, Si, V, Co

Essential Elements

• Organized by position in the periodic table:– Nonmetals:

• C, H, O, N, P, Cl, S, B

– Alkali and alkaline earth metals: • K, Mg, Ca

– Transition metals: • Mn, Fe, Ni, Cu, Zn, Mo

Representative Element Concentrations in Plants

Element Concentration (ppm)C 450000N 15000K

10000

P 2000Ca 5000Mg 2000Fe 100Zn 20Mo 0.1

Nutrient Uptake (kg/ha/yr)

N

P

K

Ca

Mg

Zn

Broccoli 165 10 210

Celery 195 50 435

New Hamp.Hardwood

116 12 67 62 10

Alfalfa 397 30 400 212 35 0.3

California Chaparral

131 7 46 74 14

Nutrient Functions in Plants

• C, H, O Main structural components of plants

• N Amino acids, nucleic acids, proteins, chlorophyll

• P phospholipids, energy transfer (ATP)

• K osmotic regulation• S proteins

Nutrient Functions in Plants

• Ca strengthens cell walls• Mg chlorophyll• Fe, Mn, enzyme activation, electron

Cu, Zn transport• B cell division• Cl osmotic regulation• Mo nitrate reductase enzyme

Nutrient Functions in Plants

• Co essential for N fixation• V oxidation reduction reactions• Na essential for halophytes, osmotic

regulation• Si required for some grasses,

strengthens cell walls• Ni essential for legumes, urease

enzyme

How do nutrients get into plants?

Root Morphology

Zone of mostrapid nutrientuptake

Slower nutrientuptake

Cross-section of maturation zone

Nutrient Uptake

• Apoplasmic Transport– transport in the root “free space”. Is a “dead-end”

except in the youngest part of the root.

• Symplasmic Transport - involves uptake across the plasma membrane:– Passive transport– Active transport

The Plant Cell

Nutrient Uptake• Movement through the root to the xylem

– Apoplasmic vs. Symplasmic– Apoplasmic in the youngest part of the root– Symplasmic in young and old parts of root

• Uptake into the Symplasm– Nutrients must cross plasma membrane– Active vs. Passive– Active: energy input needed– Passive: no energy input needed

Nutrient Uptake

Cell Structure

The Plant Cell

Plasma Membrane

• Function: to control the passage of water and solutes into and out of the cell

• Structure:– Phospholipid bilayer--hydrophilic outside,

hydrophobic inside. When intact is impermeable to water and solutes

– Embedded proteins: “channels” and “carriers” for passage of water and solutes. Under metabolic control.

The Plasma Membrane

Nutrient Uptake• Definition: passage of nutrient ions or

molecules across the plasma membrane. Nutrients thus taken up are then transported to the xylem for redistribution to sinks throughout the plant

• Active transport (uptake): requires direct input of energy (ATP)

• Passive transport (uptake): does not require energy

Apoplasmic vs. Symplasmic

• Most nutrients can be transported apoplasmically and symplasmically, and therefore can be taken up along the root axis.

• However, in many plant species, Ca is not transported symplasmically.– Therefore, only the youngest part of the

root system takes up Ca.– This explains why some plants are

especially susceptible to Ca deficiency.

Remobilization

• Remobilization is the movement of nutrients from one part of the plant to another. Some nutrients are mobile and some are immobile within plants.

• Remobilization from mature leaves to areas of new growth is essential to the life of the plant under conditions of limited nutrient availability (e.g wildland soils, poorly fertilized agricultural soils).

• Nutrient mobility affects where nutrient deficiencies are manifested.

Nitrogen and Corn

Ca Deficiency

Nutrient Mobility

• Mobility of a nutrient is often related to the function(s) of that nutrient in plants.

• Mobile nutrients: N, P, K, Mg, Cl

• Immobile: Ca, S, B, Fe, Mn, Cu, Mo, Zn

Nutrient Deficiencies

• Nutrient deficiency symptoms are often related to the function of that nutrient in plants.

• An "educated guess" regarding what nutrient is responsible for a particular deficiency can be made by considering the following:– position of deficiency on plant (old, young)– pattern of deficiency– color of deficiency

Deficiency Symptom

Corn

Older leaves

Interveinal chlorosis

Magnesium

Deficiency Symptom

Tomato

Fruit

“Blossom end rot”

Calcium

Deficiency Symptom

Cabbage

Older leaves

Chlorosis

Nitrogen

Deficiency Symptom

Cotton

Younger leaves

Interveinal chlorosis

Iron

Deficiency Symptom

Alfalfa

Older leaves

Spotting, necrosis

Potassium

Deficiency Symptom?

Grapes

All leaves

Marginal burning,necrosis

Salt, sodium toxicity