A plant nutrient is called an essential element if the plant fails to complete its life cycle or grows abnormally when the element is absent or insufficient. Essential elements (Table 35.1) fall roughly into two categories—
| Element (abbreviation; absorbed form) | Typical amount in plant (g/kg dry wt) |
Major functions | Deficiency symptoms |
|---|---|---|---|
| Macronutrients | |||
| Nitrogen (N; NO3– and NH4+) | 15 | In proteins, nucleic acids | Oldest leaves turn yellow and die prematurely; plant is stunted |
| Phosphorus (P; H2PO4– and HPO42– |
2 | In nucleic acids, ATP, phospholipids, and phosphoproteins | Plant is dark green with purple veins and is stunted |
| Potassium (K; K+) | 10 | Enzyme activation; water balance; ion balance; stomatal opening | Older leaves have dead edges |
| Sulfur (S; SO24– |
1 | In proteins and coenzymes | Young leaves are yellow to white with yellow veins |
| Calcium (Ca; Ca2+) | 5 | Affects the cytoskeleton, membranes, and many enzymes; second messenger | Growing points die back; young leaves are yellow and crinkly |
| Magnesium (Mg; Mg2+) | 2 | In chlorophyll; required by many enzymes; stabilizes ribosomes | Older leaves have yellow stripes between veins |
| Micronutrients | |||
| Iron (Fe; Fe2+ and Fe3+) | 0.1 | In active site of many redox enzymes and electron carriers; chlorophyll synthesis | Young leaves are white or yellow |
| Chlorine (Cl; Cl–) | 0.1 | Photosynthesis; ion balance | Leaf tips wilt; leaves turn yellow and die |
| Manganese (Mn; Mn2+) | 0.05 | Cofactor for many enzymes | Younger leaves are pale with green veins |
| Boron [B; B(OH)3] | 0.02 | Required for proper cell wall formation and expansion | Poor growth of leaves and roots |
| Zinc (Zn; Zn2+) | 0.02 | Enzyme activation; auxin synthesis | Young leaves are abnormally small; older leaves have many dead spots |
| Copper (Cu; Cu2+) | 0.006 | Cofactor for some redox enzymes and electron carriers | New leaves are dark green, may have dead spots |
| Nickel (Ni; Ni2+) | 0.001 | Activation of the enzyme urease | Leaf tips die; deficiency is rare |
| Molybdenum (Mo; MoO42– |
0.0001 | Cofactor of enzymes involved in nitrogen reduction | Leaves turn yellow between veins; older leaves die |
A plant needs macronutrients in concentrations of at least 1 gram per kilogram of the plant’s dry matter.
A plant needs micronutrients in concentrations of less than 100 milligrams per kilogram of the plant’s dry matter.
How do we know if a plant is getting enough of a particular nutrient?