EFB530 Plant Physiology

Mineral nutrition

Plant are sessile and autotrophic

• must obtain the nutrients they need to live on from the medium in which they grow - soil is a plant's supermarket
• mechanisms have evolved in plants to allow them to survive in media with varying nutrient properties
• plants are the primary agents of mineral incorporation into the biosphere-they are biology's miners

• collect plant tissues, dry them down, chemically assay the elements that have been taken up by the plant (see the Table below)
• when we do that - find that there are alot of different elements in plant tissue

How do we figure out which ones are essential for plant growth and reproduction -which were taken up, but are not needed by the plant

• Try to grow plants in a precisely defined medium, then remove individual components and observe the effect on growth
• Do this using hydroponics - growing plants in a liquid medium, with precise concentrations of elements added to absolutely pure water, must keep the liquid oxygenated

1) Required for normal growth and completion of the life cycle

2) Not replaceable under normal growth conditions

3) Have a demonstrated biological role in the plant - structural or physiological function

There are 17 essential elements

H hydrogen; O oxygen; C carbon

• Obtained mostly from water and O₂ & CO₂ from the atmosphere

N, K, Ca, P, Mg, S - Macronutrients

• generally required in large amounts (0.1-5 % by dry weight)

Fe, Cl, Cu, Mn, Zn, Mo, B, Ni - Micronutrients

• required in trace quantities
• not discovered until techniques for generating & handling very pure water were used

Na, Co, Si - Required by some plants

• Na and Co are taken up by plants - are generally not required - BUT are required in the nutrition of the animals that eat plants

Dennis Hoagland developed a defined mineral solution that has an optimum mixture of the essential elements = Hoagland's solution

• includes N from both NH₄ and from NO₃

• Since we know at the molecular level how the elements function, we can begin to predict some of the effects of a deficiency in that element
• vice versa, deficiency symptoms of an element begin to give clues about its function
• although most elements serve multiple functions

Plants will focus resources to newly growing tissues or to reproductive tissues & seeds, if that is possible

• some elements can be remobilized by the plant =mobile elements
• some are fixed in location once they are deposited=immobile elements

Immobile elements - S, Ca, Fe, Mn, B, Cu, Zn

• Ca is locked into the cell walls
• metals are not easily metabolized or transported
• deficiency symptoms seen in young leaves first

Mobile elements - N, P, K, Mg

• N, P can be metabolized easily, K, Mg quite mobile
• deficiency seen first in older leaves

What is the distribution of nutrients in the plant?

• generally much higher accumulation of nutrients (by % dry weight) in the leaves compared with the wood
• by harvesting a whole plant - can remove much greater proportion of the nutrients from the system

Mineral deficiencies in the soil can be restored by adding fertilizer

• usual deficiencies are in N, P, or K; can supplement with chemical fertilizer
• N=ammonium nitrate; P=phosphate; K=muriate of potash
• organic fertilizers also replenish these components and add water holding capacity to the soil

Mineral deficiency can occur when the minerals are inaccessible to the plant do to alkaline or acidic pH

• most minerals form soluble carbonates at moderately low pH - these can be taken up by the plant
• at alkaline (high) pH or very low pH, some minerals become inaccessible - lime can be added to raise the soil pH to a range optimum for nutrient uptake