What makes up a plant?
Jean-Bapiste von Helmont in the 1600's wanted to know why plants could get bigger without apparently using soil they grew in. He designed an experiment to determine how much soil a plant actually used and discovered that a 5 year old willow tree used only about 0.5% of the soil that it was grown in. Thus most of the material that makes up a plant must come from gases or water.
After plants are desiccated, analysis show that 95% of the dry weight material is of organic production (carbons chains [ CHO] ; carbohydrates, proteins, lipids), and only 5% is of inorganic derivation (minerals and the like).
Nutrients required for growth:
Water as we discussed earlier under xylem dynamics is essential for plant life. Plants need water for: respiration & photosynthesis, transport of sugars, transpiration/ cooling of plants, absorption of nutrients, and for structure ( turgor pressure).
In addition to water, other inorganic nutrients are need for survival, growth, and reproduction:
Element
Form used by plant
% by fresh weight of plant
Carbon
CO3--, HCO3- , CO2
45
Hydrogen
H+ (water)
8
Oxygen
H2O, other oxides
41
MACRONUTRIENTS
Nitrogen
ammonium (NH4) ions, or as nitrate (NO3) ions
2
Phosphorus
HPO4--, H2PO4-
0.4
Potassium
K+
1.1
Calcium
Ca++
0.6
Magnesium
Mg++
0.3
Sulfur
SO3--, SO4--
0.5
MICRONUTRIENTS
Iron Fe
Fe++, Fe+++
0.02
essential for the synthesis of chlorophyll. Manganese Mn
Mn++, Mn+++
0.05
may substitute for Mg by activating certain phosphate-transferring enzymes Copper Cu
Cu+, Cu++
0.001
activates many enzymes:deficiency interferes with protein synthesis and causes a buildup of soluble N compounds Zinc Zn
Zn++
0.01
controls the synthesis of indoleacetic acid, which dramatically regulates plant growth Molybdenum Mo
MoO4--
0.0001
functions largely in the enzyme systems of N fixation and nitrate reduction. Boron B
BO3---
0.005
regulates the metabolism of carbohydrates Chlorine Cl
Cl-
<0.0001
NOTE: Some plants require others trace elements for growth. However, these are case specific and thus we won't elaborate on them here.
Rather than go over the role of each of the nutrients, I've selected the following nutrients all of which, except Cu, are macronutrients and often can be found to be deficient especially in soils used heavily for agricultural purposes:
Nitrogen
N is a part of all living cells including all proteins, enzymes and metabolic processes involved in the synthesis and transfer of energy.
* Nitrogen iis a constitutent of chlorophyll
* N helps plants with rapid growth, increasing seed and fruit production and improving the quality of leaf and forage crops.
- Nitrogen deficiencies appear in crops as a yellowing of older plant tissue and general stunting of plants. When soil nitrate levels are high, plants can accumulate nitrates in certain tissues above what is needed at that stage of growth. A shortage of nitrogen will cause the plant to mobilize extra nitrate stored in older tissue and send it to younger, developing tissue.
Phosphorous
- Plants absorb phosphorus (P) as either HPO4-2 or H2PO4-1 ions. Soil pH is the important fact in determining which ion is most dominant in the soil solution.
- P is an essential part of the process of photosynthesis.
* Involved in the formation of all oils, sugars, starches.
* Helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress.
* Effects rapid growth.
* Encourages blooming and root growth.
- A soil solution containing only a few parts per million of phosphate ions is usually considered adequate for plant growth. Concentrations of phosphate ions in the soil solution may be as low as 0.001 parts per million.
- Phosphorus deficiency often appears early in plant growth as stunting, with purple or reddish tints in the leaf and vegetative tissues of corn, barley, and some mustard crops. Phosphorus deficiency can sometimes be induced through situations that inhibit root growth, such as soil compaction or cold soil temperatures.
Potassium
- Potassium is absorbed by plants in larger amounts than any other mineral element except nitrogen and, in some cases, calcium.
- Potassium is a major cell electrolyte, used to balance charge within the plant produced from the uptake of anions such as nitrate (NO3-1), sulfate (SO4-2) and chloride (Cl-1) ions, as well as from the internal production of organic acids.
- Potassium is an enzyme activator and helps regulate stomates.
- K is involved in several enzymatic reactions, particularly those involving the adenosine phosphates (ATP and ADP). It aids in the building of protein, photosynthesis, fruit quality and reduction of diseases.
- In many plants, such as corn, wheat and bean, potassium deficiency results in stunted plants and yellowing of the outer leaf margins of older leaves. Severe deficiency can advance the yellowing into necrosis, or a "scorched" appearance. Advanced stages will show general bronzing of the areas between the leaf veins. Leaf tissue will eventually brown and die, but petioles will remain green for some time.
Calcium
- Calcium, is an essential part of plant cell wall structure, and provides for normal transport and retention of other elements as well as strength in the plant. It is also thought to counteract the effect of alkali salts and organic acids within a plant.
- Calcium levels are dependent on the soil makeup...calcareous soils derived from limestone may be high in Ca while those soils derived from granitic or mafic sources may be low.
- Calcium is not readily translocated between plant tissues, and plants do not accumulate high calcium concentrations when it is in excess. Proper development of fruits and storage roots are dependent on a constant soil supply of calcium. Deficiency in tomato is characterized as blossom end rot.
- Calcium deficiency is hard to detect with plant analysis or soil testing, because it is usually caused by low soil water uptake by the plant. The Ca may be in the soil but it is not being taken up.
Copper
- Several enzymes include copper in their structure. Copper is also part of several compounds important in photosynthesis.
- A deficiency interferes with protein synthesis and causes a buildup of soluble N compounds. Excess quantities of Cu may also induce Fe deficiency.
- Deficiency shows as deformed tops in younger plant tissue of broadleaf plants. Flowering is reduced and ovules are often aborted.
Magnesium
- Magnesium is the central element within the chlorophyll molecule. It is also an essential element in the production of proteins and activator of several enzymes = cofactor
- Magnesium deficiency is shown first by the yellowing of older leaves. The yellowing is usually interveinal initially. Later on, the leaf margins can appear similar to potassium deficiency.
- Sulfur
* Essential plant food for production of protein.
* Promotes activity and development of enzymes and vitamins.
* Helps in chlorophyll formation.
* Improves root growth and seed production.
* Helps with vigorous plant growth and resistance to coldWhere and how do plants obtain these nutrients?........ continue on to the soil page
Note: sometimes too much is too good.....
Oxygen is needed for respiration. However, if the soil is water saturated then there will be no pockets of air and in effect the roots will suffocate. This is one reason why the overwatering of a plant is detrimental ( another is it encourages the growth of fungi which will result in damping off or root rot).