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31.1C: Essential Nutrients for Plants - Biology

31.1C: Essential Nutrients for Plants - Biology


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Approximately 20 macronutrients and micronutrients are deemed essential nutrients to support all the biochemical needs of plants.

Learning Objectives

  • Distinguish among the essential nutrients for plants

Key Points

  • An element is essential if a plant cannot complete its life cycle without it, if no other element can perform the same function, and if it is directly involved in nutrition.
  • An essential nutrient required by the plant in large amounts is called a macronutrient, while one required in very small amounts is termed a micronutrient.
  • Missing or inadequate supplies of nutrients adversely affect plant growth, leading to stunted growth, slow growth, chlorosis, or cell death.
  • About half the essential nutrients are micronutrients such as boron, chlorine, manganese, iron, zinc, copper, molybdenum, nickel, silicon, and sodium.

Key Terms

  • micronutrient: a mineral, vitamin, or other substance that is essential, even in very small quantities, for growth or metabolism
  • chlorosis: a yellowing of plant tissue due to loss or absence of chlorophyll
  • macronutrient: any of the elements required in large amounts by all living things

Essential Nutrients

Plants require only light, water, and about 20 elements to support all their biochemical needs. These 20 elements are called essential nutrients. For an element to be regarded as essential, three criteria are required:

  1. a plant cannot complete its life cycle without the element
  2. no other element can perform the function of the element
  3. the element is directly involved in plant nutrition

Macronutrients and Micronutrients

The essential elements can be divided into macronutrients and micronutrients. Nutrients that plants require in larger amounts are called macronutrients. About half of the essential elements are considered macronutrients: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. The first of these macronutrients, carbon (C), is required to form carbohydrates, proteins, nucleic acids, and many other compounds; it is, therefore, present in all macromolecules. On average, the dry weight (excluding water) of a cell is 50 percent carbon, making it a key part of plant biomolecules.

The next-most-abundant element in plant cells is nitrogen (N); it is part of proteins and nucleic acids. Nitrogen is also used in the synthesis of some vitamins. Hydrogen and oxygen are macronutrients that are part of many organic compounds and also form water. Oxygen is necessary for cellular respiration; plants use oxygen to store energy in the form of ATP. Phosphorus (P), another macromolecule, is necessary to synthesize nucleic acids and phospholipids. As part of ATP, phosphorus enables food energy to be converted into chemical energy through oxidative phosphorylation. Light energy is converted into chemical energy during photophosphorylation in photosynthesis; and into chemical energy to be extracted during respiration. Sulfur is part of certain amino acids, such as cysteine and methionine, and is present in several coenzymes. Sulfur also plays a role in photosynthesis as part of the electron transport chain where hydrogen gradients are key in the conversion of light energy into ATP. Potassium (K) is important because of its role in regulating stomatal opening and closing. As the openings for gas exchange, stomata help maintain a healthy water balance; a potassium ion pump supports this process.

Magnesium (Mg) and calcium (Ca) are also important macronutrients. The role of calcium is twofold: to regulate nutrient transport and to support many enzyme functions. Magnesium is important to the photosynthetic process. These minerals, along with the micronutrients, also contribute to the plant’s ionic balance.

In addition to macronutrients, organisms require various elements in small amounts. These micronutrients, or trace elements, are present in very small quantities. The seven main micronutrients include boron, chlorine, manganese, iron, zinc, copper, and molybdenum. Boron (B) is believed to be involved in carbohydrate transport in plants; it also assists in metabolic regulation. Boron deficiency will often result in bud dieback. Chlorine (Cl) is necessary for osmosis and ionic balance; it also plays a role in photosynthesis. Copper (Cu) is a component of some enzymes. Symptoms of copper deficiency include browning of leaf tips and chlorosis (yellowing of the leaves). Iron (Fe) is essential for chlorophyll synthesis, which is why an iron deficiency results in chlorosis. Manganese (Mn) activates some important enzymes involved in chlorophyll formation. Manganese-deficient plants will develop chlorosis between the veins of its leaves. The availability of manganese is partially dependent on soil pH. Molybdenum (Mo) is essential to plant health as it is used by plants to reduce nitrates into usable forms. Some plants use it for nitrogen fixation; thus, it may need to be added to some soils before seeding legumes. Zinc (Zn) participates in chlorophyll formation and also activates many enzymes. Symptoms of zinc deficiency include chlorosis and stunted growth.

Deficiencies in any of these nutrients, particularly the macronutrients, can adversely affect plant growth. Depending on the specific nutrient, a lack can cause stunted growth, slow growth, or chlorosis. Extreme deficiencies may result in leaves showing signs of cell death.


Top 10 Essential Elements of Micronutrients | Plants

The following points highlight the top ten essential elements of Micronutrients. The elements are: 1. Iron 2. Manganese 3. Boron 4. Molybdenum 5. Zinc 6. Copper 7. Chlorine 8. Sodium 9. Cobalt 10. Silicon.

Micronutrients Element # 1.

Iron:

Iron is mainly absorbed by the plant in the ferrous form, but ferric ion may also be absorbed. Soils are usually not deficient in iron, but they may be deficient in soluble forms of iron. Availability of iron to the plant is controlled by the soil pH. Acid soil favours availability of soluble forms of iron. However, in neutral or alkaline soils, iron is much more insoluble.

Iron performs a number of important functions in the overall plant metabolism. Like other elements, it functions both as a structural component and as a cofactor for enzymatic reactions.

Oxidation-reduction reactions are most commonly associated with iron containing enzymes. Iron is a transition metal, as it exists in more than one oxidation states. That is why, it can accept or donate electrons according to the redox potential of the reactants.

Physiological Role of Iron:

(i) A large portion of iron is found associated with porphyrins in the form of cytochromes, which are necessary for the electron transport system in mitochondria as well as chloroplasts.

(ii) Iron is a component of ferredoxin which is indispensable for the light reactions of photosynthesis and N2-fixation.

(iii) Iron is a constituent of the enzymes catalase and peroxidase, which involve molecular oxygen directly in oxidation-reduction reactions.

(iv) Iron is essential for the synthesis of chlorophyll, but where does iron have its effect on chlorophyll synthesis, is uncertain.

(v) Ferrous form of iron is required for the aconitase reaction in TCA cycle. By coordinate bond formation with the enzyme molecule the ferrous iron helps in substrate recognition and binding.

(vi) Ferric form of iron is required for amylase synthesis in GA-treated barley aleurone layer.

(vii) Iron has also been identified as a component of various flavo-proteins active in biological oxidations.

(viii) Iron is a constituent of leghaemoglobin, which is found in root nodules of leguminous plants. This leghaemoglobin by means of its iron atom protects nitrogenase of bacteroids from oxygen inactivation.

(ix) Iron is a constituent of N2-ase enzyme which is responsible for biological nitrogen fixation both in free living and symbotic bacteria.

Deficiency Symptoms of Iron:

Pronounced interveinal chlorosis occurring first on the youngest leaves, results in iron-deficient plants.

Sometimes interveinal chlorosis is followed by chlorosis of the veins, so the whole leaf then becomes yellow. In severe cases, the young leaves may even become white with necrotic lesions. The symptom may be general or sometimes strictly local. This is due to the fact that iron does not move freely from the older to the younger leaves.

Micronutrients Element # 2.

Manganese:

Manganese exists in the soil in divalent, trivalent, and tetravalent forms, but it is absorbed largely as the divalent manganous cation (Mn 2+ ). Much of the manganese of the soil is present in insoluble compounds in the tri- and tetravalent forms and only a little amount in the bivalent form and thus is largely unavailable to the plant.

In poorly aerated acid soils, the tri- and tetravalent forms are reduced to the bivalent form, thus it becomes available to the plants. Well-aerated alkaline soils, on the other hand, favours the oxidation of manganese to form unavailable manganese oxides, such as Mn2O3 and MnO2.

Functions of Manganese:

(i) Manganese is involved in oxidation-reduction processes together with decarboxylation and hydrolytic reactions.

(ii) Manganese plays an important role in photosynthesis. Photosystem II in chloroplast contains manganese protein. Four Mn 2+ ions are bound to one or more proteins and a chloride ion bridges two Mn 2+ together. The Mn-protein is a part of the inner side of the thylakoid membrane and is involved directly in H2O oxidation (Barber. 1984) and thus O2 evolution.

(iii) Manganese can replace magnesium in many of the phosphorylating and group-transfer reactions like hexokinase, glucokinase, phosphoglucokinase, phosphoglucomutase, adenosine kinase, etc.

(iv) Manganese is the predominant metal ion of Krebs cycle reactions.

(v) Manganese acts as an activator for the enzymes nitrite reductase and hydroxylamine reductase.

(vi) Manganese is absolutely required by the NAD-malic enzyme system found in leaves of aspartate type C4 plants.

(vii) RNA-polymerase has an absolute requirement for manganese or magnesium.

(viii) Manganese, along with magnesium has been found to be essential for optimal activity of the enzyme responsible for the formation of phosphatidyl inositol.

(ix) There is considerable evidence that manganese influences the level of auxin in plant tissues. It enhances the IAA oxidase activity.

Deficiency Symptoms of Manganese:

(i) Mottled chlorosis with necrotic spots appear in the interveinal areas of the leaf.

(ii) In manganese deficiency, chloroplast is markedly affected. The chloroplasts lose chlorophyll and starch grains, become yellowish, vacuolated and granular, and finally disintegrate.

Micronutrients Element # 3.

Boron:

Boron is absorbed by the plants from the soil as un-dissociated boric acid (H3BO3). Boron is also present in the soil as calcium or manganese borates. The dissolved boron content is very low in the soil solution. The amount of boron is higher in acid soils. With the increase in pH of the soil, boron becomes less available to the plants.

It is evident that essentiality of boron for all green plants is not absolute. It is required by higher green plants and diatoms but has not been shown to be essential for all species of green algae.

In higher plants boron performs the following important functions:

(i) Boron is essential for sugar transport. It complexes with sugar. Owing to their negative charge, the sugar borate complexes might pass through a negatively charged membrane more readily than neutral sugar molecules. Boron reacts with membrane constituents to form borate loci or borate reaction centres on membranes. These loci or centres might facilitate the passage of sugar through membranes.

It was suggested that boron might perform this role either:

(a) Through formation of sugar borate complexes which traverse membranes more readily than non-borated sugar molecules, or

(b) Through the formation of boron loci on membranes which facilitate the passage of sugars. The second suggestion is favoured as the mode of action of boron.

(ii) Boron is essential for the formation of pectin from uridine diphosphate D-glucose. Thus, boron is concerned with the cell wall metabolism specially involved in cell wall bonding.

(iii) Boron is involved in the polymerization of lignin precursors.

(iv) Dugger (1957) postulated that boron inhibits conversion of sugar to starch. Boron inhibits starch formation by forming an unreactive glucose-1 -phosphate-boron complex.

(v) Boron helps in germination and growth of pollen grains.

(vi) Boron along with GA3 influences the α-amylase activity in germinating seeds. Boron apparently has a regulatory role in synthesis of GA3.

(vii) Boron is essential for DNA synthesis.

The biochemical and physiological functions proposed for boron were reviewed by Dugger (1983), Philbeam and Kirkby (1983) and Lovatt and Dugger (1984). No specific function is yet certain, but evidence favours special involvement of boron in nucleic acid synthesis and some unclear functions in membranes.

Deficiency Symptoms of Boron:

(i) Boron deficiency results in ‘heart rot’ of beets, ‘water core’ of turnip, ‘stem crack’ of celery and ‘drought spot’ of apples.

(ii) Root tip elongation is inhibited.

(iv) Nodule formation in legumes does not occur.

(v) The branches at the ends of twig form a rosette.

Micronutrients Element # 4.

Molybdenum:

Molybdenum is present in the soil as dissolved molybdate ions, in an exchangeable form adsorbed to soil particles, and in a non-exchangeable form. It is absorbed by the plants as molybdate ions (MoO4 2- ).

Functions of Molybdenum:

(i) Initially molybdenum was shown to be essential for nitrogen fixation by Azotobacter chroococcum.

(ii) Later it was also found to be essential in nitrogen fixation by legumes.

(iii) Molybdenum is a component of the enzyme nitrate reductase, which is a sulphydryl, metallo-FAD-protein containing Mo.

(iv) Molybdenum is a component of nitrogenase found in nitrogen fixing organisms. The enzyme consists of two components or fractions known as component I or fraction I containing molybdenum and iron, and component II or fraction II containing iron.

Deficiency Symptoms of Molybdenum:

(i) Molybdenum deficiency causes chlorotic interveinal mottling of the leaves with marginal necrosis and in-folding of leaves.

(ii) In crucifers molybdenum deficiency causes ‘whitetail’ disease, the partial or complete withering of leaf lamina except the midrib.

(iii) In severe deficiency the mottled areas become necrotic and may cause the leaf wilt.

(iv) The flowers abscise before fruit setting.

Micronutrients Element # 5.

Zinc:

Zinc is absorbed as divalent Zn 2+ ion. The sources of zinc in the soil are ferromagnesian minerals, magnetite and biotite. Zinc is released from these minerals. Soil pH is the main factor for the availability of zinc.

Zinc is an essential microelement performing the following important functions:

(i) Zinc is associated most commonly with the biosynthesis of indole-3-acetic acid (an auxin). Skoog suggested that zinc prevented oxidation of IAA. Zinc is essential for the biosynthesis of tryptophan which is the precursor of auxin. So, through the synthesis of tryptophan zinc affects auxin levels.

(ii) Zinc is essential for the activity of many enzymes like pyridine nucleotide dehydrogenases, alcohol dehydrogenase, glucose-6-phosphate and triose phosphate dehydrogenases. Zn 2 + is involved in binding NAD to the enzyme protein.

(iii) Zn 2+ is required by the enzyme phosphodiesterase.

(iv) The enzyme carbonic anhydrase requires Zn 2 + for maximal activity. Zinc acts as a metal activator of this enzyme.

(v) Zn 2+ induces de novo synthesis of cytochrome.

(vi) Zn 2 + participates in chlorophyll formation and prevents chlorophyll destruction.

Deficiency Symptoms of Zinc:

Zinc deficiency shows the following symptoms:

(i) Interveinal chlorosis of the older leaves starts at the tips and margins.

(ii) Growth is stunted in severe zinc deficiency.

(iii) The leaves become smaller and the internodes shorten to give a rosette form.

Micronutrients Element # 6.

Copper:

Copper is sufficiently available in nearly all soils. It is absorbed as both divalent and monovalent cations. Copper source in the soil is chalcopyrite (CuFeS2).

Copper is required by plants in very minute amounts and copper performs the following important functions:

(i) Copper is a component of cytochrome a, which is further a component of cytochrome c oxidase complex. This copper atom alternates between a+ 2 oxidized form and a + 1 reduced form as it transfers electrons from cytochrome a3 to molecular oxygen (Nason and McElroy, 1963).

(ii) In the thylakoid membrane, there is an electron carrier which is a small copper containing protein named plastocyanin. It remains bound loosely to the inside of thylakoid membrane. When the copper atom of plastocyanin becomes reduced from Cu 2 + to Cu 1 + by PS II, it can move along the membrane carrying an electron to PS I where it is re-oxidized to the Cu 2+ form.

(iii) Copper is found in a group of enzymes in which oxygen is used directly in the oxidation of substrate. These enzymes are tyrosinase, laccase, and ascorbic acid oxidase.

The general reaction is:

Here also copper mediates the enzyme transformations by undergoing cyclic oxidation and reduction: (Price, 1970).

(iv) Copper has an indirect effect on nodule formation (Cartwright and Halls-worth, 1970). Copper deficiency reduces cytochrome oxidase activity, which in turn increases oxygen – levels in the nodule, thus restricting nitrogen fixation.

Deficiency Symptoms of Copper:

Plants are rarely deficient in copper, mainly because it is required in very minute amount.

Still there are certain copper deficiency symptoms as follows:

(i) Copper deficiency causes yellow leaf tips or reclamation disease in cereals accompanied by failure to set seeds.

(ii) Copper deficiency results in exanthema, a disease of fruit trees that is characterized by gummosis, accompanied by dieback and glossy brownish blotches on leaves and fruits.

(iii) Necrosis of the young leaf tips proceeds along the margin and gives it a withered appearance. In severe cases, the leaves fall and the whole plant tends to wilt.

Micronutrients Element # 7.

Chlorine:

No chloride-containing compound has been found in higher plants. It appears that it is not so essential in most higher plants.

Still it performs some important functions as follows:

(i) Chloride ion is involved in the primary process of oxygen evolution. PS II contains one or more proteins containing manganese, called manganese protein which is involved directly in the first step of H2O oxidation. It is thought that a chloride ion bridges two Mn 2 + together.

(ii) During stomatal opening in light there is an influx of both potassium and chloride ions into the guard cells from subsidiary cells, giving osmotic potentiality to the guard cells. But the exact role of CI – ion in stomatal opening is not clear.

Micronutrients Element # 8.

Sodium:

Sodium is not essential for many plants, but its essentiality is restricted to certain species normally found in high saline environments. Sodium has been found to be essential for Artiplex vesicaria, Halogeton glomeratus, etc. Sodium can partially replace potassium in many of the reactions known to require potassium. Sodium is apparently necessary for C4 carbon fixation in certain plant species.

Aeluropus litoralis, a halophyte, has been found to fix carbon through C3 pathway when depleted of sodium. If a C3 plant is grown in presence of sodium, the photosynthetic pathway is shifted to C4 mode. It was also demonstrated that sodium influences the balance between PEP- carboxylase and RuBisCO in maize.

Certain CAM plants show a requirement for Na for the expression of Crassulacean acid metabolic pathway. If the plants are treated with NaCl, CO2 uptake is increased in the dark with the increase in malate content in the leaves. Sodium plays a role in maintaining a favourable water balance in plants.

Micronutrients Element # 9.

Cobalt:

Cobalt is required by the symbiotic organisms for nitrogen fixation. It is also involved in leghaemoglobin metabolism. In Rhizobium ribonucleotide reductase requires cobalt for maximum activity.

Micronutrients Element # 10.

Silicon:

Silicon is essential for the formation of silicified walls of diatoms. Growth of the diatom cells is directly proportional to the concentration of the silicon in the medium. Silicon reduces toxicity of other elements.


Secondary Plant Nutrients: Calcium, Magnesium, and Sulfur

Calcium, magnesium, and sulfur are essential plant nutrients. They are called “secondary” nutrients because plants require them in smaller quantities than nitrogen, phosphorus, and potassium. On the other hand, plants require these nutrients in larger quantities than the “micronutrients” such as boron and molybdenum.

Calcium, magnesium, and sulfur are generally adequate in most Mississippi soils with favorable pH and organic matter levels. They affect pH when applied to the soil. Calcium and magnesium both increase soil pH, but sulfur from some sources reduces soil pH. Compounds containing one or more of these nutrients are often used as soil amendments rather than strictly as suppliers of plant nutrition.

Calcium

The primary function of calcium in plant growth is to provide structural support to cell walls. Calcium also serves as a secondary messenger when plants are physically or biochemically stressed.

Calcium deficiencies rarely occur in Mississippi soils. Soils with favorable pH levels are normally not deficient in calcium. Acid soils with calcium contents of 500 pounds per acre or less are deficient for legumes, especially peanuts, alfalfa, clovers, and soybeans. At this level, limited root system crops such as tomatoes, peppers, and cucurbite would also need additional calcium. Soluble calcium is available as the Ca2+ ion and is needed for peanuts at pegging time and for peppers and tomatoes to prevent blossom end rot.

Available calcium can be lost from the soil when it is (a) dissolved and removed in drainage water, (b) removed by plants, (c) absorbed by soil organisms, (d) leached from the soil in rain water, or (e) absorbed by clay particles. Deficiency symptoms include death at the growing point, abnormally dark green foliage, weakened stems, shedding flowers, and any combination of these.

Limestone is the primary source of calcium in Mississippi. Other common sources include basic slag, gypsum, hydrated lime, and burned lime. These sources are recommended for peanuts, peppers, and tomatoes. In peanuts, they prevent pops and encourage pegging. In tomatoes and peppers, they prevent pops and blossom end rot. Hydrated lime and burned lime contain more readily available calcium than do basic slag and gypsum. Gypsum does not affect soil pH even though it contains calcium.

Magnesium

Magnesium is adequate for crop production in most Mississippi soils except the coarse sandy soils of the Coastal Plains and the heavy dark clays of the Blackbelt Prairie. Magnesium is absorbed as the Mg2+ ion and is mobile in plants, moving from the older to the younger leaves. It leaches from the soil like calcium and potassium.

Magnesium is the central atom amid four nitrogen atoms in the chlorophyll molecule, so it is involved in photosynthesis. It serves as an activator for many enzymes required in plant growth processes and stabilizes the nucleic acids.

Interveinal chlorosis is a deficiency symptom in crops such as legumes, corn, sorghum, cotton, and certain leafy vegetables. (Interveinal chlorosis is a yellowing between the veins while the veins remain green.) The leaves may become pink to light red and may curl upward along the margins.

To correct magnesium deficiency in soil, use dolomitic lime when lime is needed use soluble sources of magnesium when lime is not needed. Magnesium supplementation may be needed for cotton production in the Blackland Prairie.

Cattle are often affected by grass tetany when forage magnesium content is low. Other factors include nitrogen, calcium, and potassium levels, stage of growth (usually in spring), whether or not cattle are lactating, and seasonal conditions. Dolomitic limestone is recommended as a liming material where grass tetany has been a problem. Give grazing animals supplemental magnesium and calcium when grass tetany is an issue. For more detailed information on grass tetany issues, see Extension Publication 2484 Mineral and Vitamin Nutrition for Beef Cattle.

The most common soluble sources of magnesium to use as fertilizer are magnesium sulfate (containing 10% Mg and 14% S, also known as Epsom salt), sulphate of potash magnesia (containing 11.2% Mg, 22% S, and 22% K2O, commercially sold as K-Mag), and magnesium oxide (containing 55% Mg, also known as magnesia).

Sulfur

Sulfur is needed in fairly large quantities by most crops. It is an essential building block in chlorophyll development and protein synthesis. Sulfur is required by the rhizobia bacteria in legumes for nitrogen fixation. In general, crops remove about as much sulfur as they do phosphorus. Grasses remove sulfur more efficiently than legumes, and clovers often disappear from pasture mixtures when sulfur is low.

The sulfate ion, SO4, is the form primarily absorbed by plants. Sulfate is soluble and is easily lost from soils by leaching. As sulfate is leached down into soil, it accumulates in heavier (higher clay content) subsoils. For this reason, testing for sulfur in topsoil is unreliable for predicting sulfur availability during a long growing season.

Many coarse-textured, sandy soils and loworganic matter, silty soils throughout Mississippi are sulfur deficient for crop production. Many acid soils contain metallic sulfides that release sulfur as weathering occurs.

Sulfur deficiency symptoms show on young leaves first. The leaves appear pale green to yellow. The plants are spindly and small with retarded growth and delayed fruiting. For a rapid correction of a deficiency, use one of the readily available sulfate sources.

Sulfur may be recommended for major crops in Mississippi at 8–10 pounds per acre annually in some situations. Check with local MSU Extension Service offices or area agronomists for more crop- and sitespecific information.

There are many sources of fertilizer sulfur available. Organic matter is the source of organic sulfur compounds and is the main source of soil sulfur in most Mississippi soils. Other sources of sulfur are rainfall and fertilizers that contain sulfur. Some readily available sources include ammonium sulfate (21% N and 24% S), potassium sulfate (50% K20 and 17.6% S), gypsum (32.6% CaO and 16.8% S), and zinc sulfate (36.4% Zn and 17.8% S).There are several other sulfate sources as well as less available sources of sulfur in the elemental or sulfide form.

Elemental sulfur is a good acidifying agent. An application of 500 pounds of sulfur per acre on sandy loam soil reduces the pH from 7.5 to 6.5. It takes about 3 pounds of lime to neutralize the acidity formed by 1 pound of sulfur.

Table 1. Average percentage of chemical content of major sources of calcium magnesium, and sulfur.


Macronutrients and Micronutrients

The essential elements can be divided into two groups: macronutrients and micronutrients. Nutrients that plants require in larger amounts are called macronutrients . About half of the essential elements are considered macronutrients: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. The first of these macronutrients, carbon (C), is required to form carbohydrates, proteins, nucleic acids, and many other compounds it is therefore present in all macromolecules. On average, the dry weight (excluding water) of a cell is 50 percent carbon. As shown below, carbon is a key part of plant biomolecules.

Three cellulose fibers and the chemical structure of cellulose is shown. Cellulose consists of unbranched chains of glucose subunits that form long, straight fibers.

Cellulose, the main structural component of the plant cell wall, makes up over thirty percent of plant matter. It is the most abundant organic compound on earth. Plants are able to make their own cellulose, but need carbon from the air to do so.

The next most abundant element in plant cells is nitrogen (N) it is part of proteins and nucleic acids. Nitrogen is also used in the synthesis of some vitamins. While there is an overwhelming amount of nitrogen in the air (79% of the atmosphere is nitrogen gas), the nitrogen in the air is not biologically available due to the triple bond between the nitrogen atoms. Only a few species of bacteria are capable of “fixing” nitrogen to make it bioavailable thus nitrogen is often a limiting factor for plant growth.

Phosphorus (P), another macromolecule, is necessary to synthesize nucleic acids and phospholipids. As part of ATP, phosphorus enables food energy to be converted into chemical energy through oxidative phosphorylation. Likewise, light energy is converted into chemical energy during photophosphorylation in photosynthesis, and into chemical energy to be extracted during respiration. Phosphorous is typically available in a form that is not readily taken up by plant roots the form that is bioavailable is present in small quantities and rapidly “fixed” into the bioavailable form once again. Phosphorus is therefore often a limiting factor for plant growth.

Potassium (K) is important because of its role in regulating stomatal opening and closing. As the openings for gas exchange, stomata help maintain a healthy water balance a potassium ion pump supports this process. Potassium may be present at low concentrations in some types of soil, and it is the third most common limiting factor for plant growth.

Other essential macronutrients: Hydrogen and oxygen are macronutrients that are part of many organic compounds, and also form water. Oxygen is necessary for cellular respiration plants use oxygen to store energy in the form of ATP. Sulfur is part of certain amino acids, such as cysteine and methionine, and is present in several coenzymes. Sulfur also plays a role in photosynthesis as part of the electron transport chain, where hydrogen gradients play a key role in the conversion of light energy into ATP.

Magnesium (Mg) and calcium (Ca) are also important macronutrients. The role of calcium is twofold: to regulate nutrient transport, and to support many enzyme functions. Magnesium is important to the photosynthetic process. These minerals, along with the micronutrients, which are described below, also contribute to the plant’s ionic balance.

In addition to macronutrients, organisms require various elements in small amounts. These micronutrients , or trace elements, are present in very small quantities. They include boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), silicon (Si), and sodium (Na).

Deficiencies in any of these nutrients, particularly the macronutrients, can adversely affect plant growth. Depending on the specific nutrient, a lack can cause stunted growth, slow growth, or chlorosis (yellowing of the leaves). Extreme deficiencies may result in leaves showing signs of cell death.

Photo (a) shows a tomato plant with two green tomato fruits. The fruits have turned dark brown on the bottom. Photo (b) shows a plant with green leaves some of the leaves have turned yellow. Photo (c) shows a five-lobed leaf that is yellow with greenish veins. Photo (d) shows green palm leaves with yellow tips. Nutrient deficiency is evident in the symptoms these plants show. This (a) grape tomato suffers from blossom end rot caused by calcium deficiency. The yellowing in this (b) Frangula alnus results from magnesium deficiency. Inadequate magnesium also leads to (c) intervenal chlorosis, seen here in a sweetgum leaf. This (d) palm is affected by potassium deficiency. (credit c: modification of work by Jim Conrad credit d: modification of work by Malcolm Manners)

Plants obtain inorganic elements from the soil, which serves as a natural medium for land plants. Soil is the outer loose layer that covers the surface of Earth. Soil quality is a major determinant, along with climate, of plant distribution and growth. Soil quality depends not only on the chemical composition of the soil, but also the topography (regional surface features) and the presence of living organisms. In agriculture, the history of the soil, such as the cultivating practices and previous crops, modify the characteristics and fertility of that soil.

Plants obtain food in two different ways. Autotrophic plants can make their own food from inorganic raw materials, such as carbon dioxide and water, through photosynthesis in the presence of sunlight. Green plants are included in this group. Some plants, however, are heterotrophic: they are totally parasitic and lacking in chlorophyll. These plants, referred to as holo-parasitic plants, are unable to synthesize organic carbon and draw all of their nutrients from the host plant.

Plants may also benefit from microbial partners in nutrient acquisition. Particular species of bacteria and fungi have co-evolved along with certain plants to create a mutualistic symbiotic relationship with roots. This improves the nutrition of both the plant and the microbe. The formation of nodules in legume plants and mycorrhization can be considered among the nutritional adaptations of plants. However, these are not the only type of adaptations that we may find many plants have other adaptations that allow them to thrive under specific conditions.


31.1C: Essential Nutrients for Plants - Biology

By the end of this section, you will be able to do the following:

  • Describe how plants obtain nutrients
  • List the elements and compounds required for proper plant nutrition
  • Describe an essential nutrient

Plants are unique organisms that can absorb nutrients and water through their root system, as well as carbon dioxide from the atmosphere. Soil quality and climate are the major determinants of plant distribution and growth. The combination of soil nutrients, water, and carbon dioxide, along with sunlight, allows plants to grow.

The Chemical Composition of Plants

Since plants require nutrients in the form of elements such as carbon and potassium, it is important to understand the chemical composition of plants. The majority of volume in a plant cell is water it typically comprises 80 to 90 percent of the plant’s total weight. Soil is the water source for land plants, and can be an abundant source of water, even if it appears dry. Plant roots absorb water from the soil through root hairs and transport it up to the leaves through the xylem. As water vapor is lost from the leaves, the process of transpiration and the polarity of water molecules (which enables them to form hydrogen bonds) draws more water from the roots up through the plant to the leaves ((Figure)). Plants need water to support cell structure, for metabolic functions, to carry nutrients, and for photosynthesis.

Figure 1. Water is absorbed through the root hairs and moves up the xylem to the leaves.

Plant cells need essential substances, collectively called nutrients, to sustain life. Plant nutrients may be composed of either organic or inorganic compounds. An organic compound is a chemical compound that contains carbon, such as carbon dioxide obtained from the atmosphere. Carbon that was obtained from atmospheric CO2 composes the majority of the dry mass within most plants. An inorganic compound does not contain carbon and is not part of, or produced by, a living organism. Inorganic substances, which form the majority of the soil solution, are commonly called minerals: those required by plants include nitrogen (N) and potassium (K) for structure and regulation.

Essential Nutrients

Plants require only light, water, and about 20 elements to support all their biochemical needs: these 20 elements are called essential nutrients ((Figure)). For an element to be regarded as essential, three criteria are required: 1) a plant cannot complete its life cycle without the element 2) no other element can perform the function of the element and 3) the element is directly involved in plant nutrition.

Essential Elements for Plant Growth
Macronutrients Micronutrients
Carbon (C) Iron (Fe)
Hydrogen (H) Manganese (Mn)
Oxygen (O) Boron (B)
Nitrogen (N) Molybdenum (Mo)
Phosphorus (P) Copper (Cu)
Potassium (K) Zinc (Zn)
Calcium (Ca) Chlorine (Cl)
Magnesium (Mg) Nickel (Ni)
Sulfur (S) Cobalt (Co)
Sodium (Na)
Silicon (Si)

Macronutrients and Micronutrients

The essential elements can be divided into two groups: macronutrients and micronutrients. Nutrients that plants require in larger amounts are called macronutrients. About half of the essential elements are considered macronutrients: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. The first of these macronutrients, carbon (C), is required to form carbohydrates, proteins, nucleic acids, and many other compounds it is therefore present in all macromolecules. On average, the dry weight (excluding water) of a cell is 50 percent carbon. As shown in (Figure), carbon is a key part of plant biomolecules.

Figure 2. Cellulose, the main structural component of the plant cell wall, makes up over thirty percent of plant matter. It is the most abundant organic compound on earth.

The next most abundant element in plant cells is nitrogen (N) it is part of proteins and nucleic acids. Nitrogen is also used in the synthesis of some vitamins. Hydrogen and oxygen are macronutrients that are part of many organic compounds, and also form water. Oxygen is necessary for cellular respiration plants use oxygen to store energy in the form of ATP. Phosphorus (P), another macromolecule, is necessary to synthesize nucleic acids and phospholipids. As part of ATP, phosphorus enables food energy to be converted into chemical energy through oxidative phosphorylation. Likewise, light energy is converted into chemical energy during photophosphorylation in photosynthesis, and into chemical energy to be extracted during respiration. Sulfur is part of certain amino acids, such as cysteine and methionine, and is present in several coenzymes. Sulfur also plays a role in photosynthesis as part of the electron transport chain, where hydrogen gradients play a key role in the conversion of light energy into ATP. Potassium (K) is important because of its role in regulating stomatal opening and closing. As the openings for gas exchange, stomata help maintain a healthy water balance a potassium ion pump supports this process.

Magnesium (Mg) and calcium (Ca) are also important macronutrients. The role of calcium is twofold: to regulate nutrient transport, and to support many enzyme functions. Magnesium is important to the photosynthetic process. These minerals, along with the micronutrients, which are described below, also contribute to the plant’s ionic balance.

In addition to macronutrients, organisms require various elements in small amounts. These micronutrients, or trace elements, are present in very small quantities. They include boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), silicon (Si), and sodium (Na).

Deficiencies in any of these nutrients—particularly the macronutrients—can adversely affect plant growth ((Figure)). Depending on the specific nutrient, a lack can cause stunted growth, slow growth, or chlorosis (yellowing of the leaves). Extreme deficiencies may result in leaves showing signs of cell death.

Link to Learning

Visit this website to participate in an interactive experiment on plant nutrient deficiencies. You can adjust the amounts of N, P, K, Ca, Mg, and Fe that plants receive . . . and see what happens.

Figure 3. Nutrient deficiency is evident in the symptoms these plants show. This (a) grape tomato suffers from blossom end rot caused by calcium deficiency. The yellowing in this (b) Frangula alnus results from magnesium deficiency. Inadequate magnesium also leads to (c) intervenal chlorosis, seen here in a sweetgum leaf. This (d) palm is affected by potassium deficiency. (credit c: modification of work by Jim Conrad credit d: modification of work by Malcolm Manners)

Everyday Connection

Figure 4. Plant physiologist Ray Wheeler checks onions being grown using hydroponic techniques. The other plants are Bibb lettuce (left) and radishes (right). Credit: NASA

Hydroponics

Hydroponics is a method of growing plants in a water-nutrient solution instead of soil. Since its advent, hydroponics has developed into a growing process that researchers often use. Scientists who are interested in studying plant nutrient deficiencies can use hydroponics to study the effects of different nutrient combinations under strictly controlled conditions. Hydroponics has also developed as a way to grow flowers, vegetables, and other crops in greenhouse environments. You might find hydroponically grown produce at your local grocery store. Today, many lettuces and tomatoes in your market have been hydroponically grown.

Section Summary

Plants can absorb inorganic nutrients and water through their root system, and carbon dioxide from the environment. The combination of organic compounds, along with water, carbon dioxide, and sunlight, produce the energy that allows plants to grow. Inorganic compounds form the majority of the soil solution. Plants access water though the soil. Water is absorbed by the plant root, transports nutrients throughout the plant, and maintains the structure of the plant. Essential elements are indispensable elements for plant growth. They are divided into macronutrients and micronutrients. The macronutrients plants require are carbon, nitrogen, hydrogen, oxygen, phosphorus, potassium, calcium, magnesium, and sulfur. Important micronutrients include iron, manganese, boron, molybdenum, copper, zinc, chlorine, nickel, cobalt, silicon, and sodium.

Review Questions

For an element to be regarded as essential, all of the following criteria must be met, except:

  1. No other element can perform the function.
  2. The element is directly involved in plant nutrition.
  3. The element is inorganic.
  4. The plant cannot complete its lifecycle without the element.

The nutrient that is part of carbohydrates, proteins, and nucleic acids, and that forms biomolecules, is ________.

Most ________ are necessary for enzyme function.

What is the main water source for land plants?

Free Response

What type of plant problems result from nitrogen and calcium deficiencies?

Deficiencies in these nutrients could result in stunted growth, slow growth, and chlorosis.

Research the life of Jan Babtista van Helmont. What did the van Helmont experiment show?

van Helmont showed that plants do not consume soil, which is correct. He also thought that plant growth and increased weight resulted from the intake of water, a conclusion that has since been disproven.

List two essential macronutrients and two essential micro nutrients.

Answers may vary. Essential macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Essential micronutrients include iron, manganese, boron, molybdenum, copper, zinc, chlorine, nickel, cobalt, sodium, and silicon.


Nutrients in Aquaponics

Plants need lights and nutrients to grow. In the traditional method of planting, these nutrients are sourced from the soil. However, in an aquaponic system, these nutrients come from fish waste because of the absence of soil. Nutrients have a significant role in any planting methods. In aquaponics, t here are two major categories of nutrients that are essential for the plants in an aquaponics system.

1. Macronutrients

There are six macronutrients that plants need in large amounts. These nutrients are Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), and Sulphur (S). Below are the list outlines of the function of these macronutrients within the plants.

Nitrogen is the basis of all proteins and is essential for building structures, photosynthesis, cell growth, metabolic processes, and chlorophyll production. Nitrogen is a key element in aquaponic nutrient solution and serves as a proxy indicator for other nutrients. Usually, dissolved nitrogen is in the form of nitrate, but plants can use small quantities of ammonia and free amino acid to grow. Excessive nitrogen can cause excessive plant growth resulting in lush, soft plants susceptible to diseases and insect damage and difficulty in flowering and fruiting.

Phosphorus is essential for photosynthesis and the formation of oils and sugars, and encourages germination and root development in seedlings. Phosphorus deficiency can cause low root development.

Potassium functions as a cell signaling via controlled ion flow through membranes control the stomatic opening and are involved in flower and fruit set. Potassium is involved in producing and transporting sugars, water uptake, disease resistance, and fruit ripening. All plants need potassium and can be affected by low levels of these nutrients.
Potassium deficiency in aquaponic plants needs treatment. Because a lack of potassium can negatively affect photosynthesis, which can also affect plant growth, it can also make the plant susceptible to infection or infestation that could lead to plant death.

Calcium is essential for the plants' healthy growth and sturdy cell walls and helps maintain plants' strength and shape. It is involved in the strengthening of stems and contributes to the production of flowers, fruits, and vegetables. Squash, tomatoes, and peppers are some plants susceptible to calcium deficiency.
It is essential to treat calcium deficiency to prevent ruining the harvestable fruits or vegetables. Low calcium levels can also stunt plant growth and can cause plant death.

Low magnesium is a common plant deficiency in aquaponics. Magnesium plays a vital role in the plant's internal functions. Magnesium helps in breaking down the chlorophyll. Treating magnesium deficiency is essential to the overall health and growth of the plants.

Sulfur is essential for the production of some proteins, chlorophyll, and other photosynthetic enzymes. Sulfur deficiencies are rare in aquaponics.

2. Micronutrients

Micronutrients are iron (Fe), copper (Cu), zinc (Zn), manganese (Mn), boron (B), and molybdenum (Mo). Most micronutrient deficiencies include yellowing of the leaves, but copper deficiencies can darken the leaves into green color.

Iron is used in chloroplasts and electron transport chains. Iron is essential for proper photosynthesis. Iron deficiency can be identified easily by using an iron Checker to check the iron level in your water. Another way to identify iron deficiency is by checking if the plants' leaves turn yellow, but the veins remain green, called "choloris." Iron has to be added to the system as "chelated iron." The suggested addition is 5 ml per 1 m2 of grow bed. A large quantity does not harm the system but can cause discoloration of the tank and the pipes.

Manganese is essential to the photosynthesis process of plants because it is used to catalyze water splitting during photosynthesis. Manganese deficiency can be seen by reduced plants' growth rates, a dull grey appearance, and yellowing between veins that remain green.

Boron is involved in the structural polysaccharides and glycoproteins, carbohydrate transport, and regulating some plants' metabolic pathways. Boron is also involved in reproduction and water uptake by cells.

Zinc is used by enzymes and also in chlorophyll that affects the overall size of the plants.


165 Nutritional Requirements of Plants

By the end of this section, you will be able to do the following:

  • Describe how plants obtain nutrients
  • List the elements and compounds required for proper plant nutrition
  • Describe an essential nutrient

Plants are unique organisms that can absorb nutrients and water through their root system, as well as carbon dioxide from the atmosphere. Soil quality and climate are the major determinants of plant distribution and growth. The combination of soil nutrients, water, and carbon dioxide, along with sunlight, allows plants to grow.

The Chemical Composition of Plants

Since plants require nutrients in the form of elements such as carbon and potassium, it is important to understand the chemical composition of plants. The majority of volume in a plant cell is water it typically comprises 80 to 90 percent of the plant’s total weight. Soil is the water source for land plants, and can be an abundant source of water, even if it appears dry. Plant roots absorb water from the soil through root hairs and transport it up to the leaves through the xylem. As water vapor is lost from the leaves, the process of transpiration and the polarity of water molecules (which enables them to form hydrogen bonds) draws more water from the roots up through the plant to the leaves ((Figure)). Plants need water to support cell structure, for metabolic functions, to carry nutrients, and for photosynthesis.


Plant cells need essential substances, collectively called nutrients, to sustain life. Plant nutrients may be composed of either organic or inorganic compounds. An organic compound is a chemical compound that contains carbon, such as carbon dioxide obtained from the atmosphere. Carbon that was obtained from atmospheric CO2 composes the majority of the dry mass within most plants. An inorganic compound does not contain carbon and is not part of, or produced by, a living organism. Inorganic substances, which form the majority of the soil solution, are commonly called minerals: those required by plants include nitrogen (N) and potassium (K) for structure and regulation.

Essential Nutrients

Plants require only light, water, and about 20 elements to support all their biochemical needs: these 20 elements are called essential nutrients ((Figure)). For an element to be regarded as essential , three criteria are required: 1) a plant cannot complete its life cycle without the element 2) no other element can perform the function of the element and 3) the element is directly involved in plant nutrition.

Essential Elements for Plant Growth
Macronutrients Micronutrients
Carbon (C) Iron (Fe)
Hydrogen (H) Manganese (Mn)
Oxygen (O) Boron (B)
Nitrogen (N) Molybdenum (Mo)
Phosphorus (P) Copper (Cu)
Potassium (K) Zinc (Zn)
Calcium (Ca) Chlorine (Cl)
Magnesium (Mg) Nickel (Ni)
Sulfur (S) Cobalt (Co)
Sodium (Na)
Silicon (Si)

Macronutrients and Micronutrients

The essential elements can be divided into two groups: macronutrients and micronutrients. Nutrients that plants require in larger amounts are called macronutrients . About half of the essential elements are considered macronutrients: carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium and sulfur. The first of these macronutrients, carbon (C), is required to form carbohydrates, proteins, nucleic acids, and many other compounds it is therefore present in all macromolecules. On average, the dry weight (excluding water) of a cell is 50 percent carbon. As shown in (Figure), carbon is a key part of plant biomolecules.


The next most abundant element in plant cells is nitrogen (N) it is part of proteins and nucleic acids. Nitrogen is also used in the synthesis of some vitamins. Hydrogen and oxygen are macronutrients that are part of many organic compounds, and also form water. Oxygen is necessary for cellular respiration plants use oxygen to store energy in the form of ATP. Phosphorus (P), another macromolecule, is necessary to synthesize nucleic acids and phospholipids. As part of ATP, phosphorus enables food energy to be converted into chemical energy through oxidative phosphorylation. Likewise, light energy is converted into chemical energy during photophosphorylation in photosynthesis, and into chemical energy to be extracted during respiration. Sulfur is part of certain amino acids, such as cysteine and methionine, and is present in several coenzymes. Sulfur also plays a role in photosynthesis as part of the electron transport chain, where hydrogen gradients play a key role in the conversion of light energy into ATP. Potassium (K) is important because of its role in regulating stomatal opening and closing. As the openings for gas exchange, stomata help maintain a healthy water balance a potassium ion pump supports this process.

Magnesium (Mg) and calcium (Ca) are also important macronutrients. The role of calcium is twofold: to regulate nutrient transport, and to support many enzyme functions. Magnesium is important to the photosynthetic process. These minerals, along with the micronutrients, which are described below, also contribute to the plant’s ionic balance.

In addition to macronutrients, organisms require various elements in small amounts. These micronutrients , or trace elements, are present in very small quantities. They include boron (B), chlorine (Cl), manganese (Mn), iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni), silicon (Si), and sodium (Na).

Deficiencies in any of these nutrients—particularly the macronutrients—can adversely affect plant growth ((Figure)). Depending on the specific nutrient, a lack can cause stunted growth, slow growth, or chlorosis (yellowing of the leaves). Extreme deficiencies may result in leaves showing signs of cell death.

Visit this website to participate in an interactive experiment on plant nutrient deficiencies. You can adjust the amounts of N, P, K, Ca, Mg, and Fe that plants receive . . . and see what happens.



Hydroponics Hydroponics is a method of growing plants in a water-nutrient solution instead of soil. Since its advent, hydroponics has developed into a growing process that researchers often use. Scientists who are interested in studying plant nutrient deficiencies can use hydroponics to study the effects of different nutrient combinations under strictly controlled conditions. Hydroponics has also developed as a way to grow flowers, vegetables, and other crops in greenhouse environments. You might find hydroponically grown produce at your local grocery store. Today, many lettuces and tomatoes in your market have been hydroponically grown.

Section Summary

Plants can absorb inorganic nutrients and water through their root system, and carbon dioxide from the environment. The combination of organic compounds, along with water, carbon dioxide, and sunlight, produce the energy that allows plants to grow. Inorganic compounds form the majority of the soil solution. Plants access water though the soil. Water is absorbed by the plant root, transports nutrients throughout the plant, and maintains the structure of the plant. Essential elements are indispensable elements for plant growth. They are divided into macronutrients and micronutrients. The macronutrients plants require are carbon, nitrogen, hydrogen, oxygen, phosphorus, potassium, calcium, magnesium, and sulfur. Important micronutrients include iron, manganese, boron, molybdenum, copper, zinc, chlorine, nickel, cobalt, silicon, and sodium.

Review Questions

For an element to be regarded as essential, all of the following criteria must be met, except:

  1. No other element can perform the function.
  2. The element is directly involved in plant nutrition.
  3. The element is inorganic.
  4. The plant cannot complete its lifecycle without the element.

The nutrient that is part of carbohydrates, proteins, and nucleic acids, and that forms biomolecules, is ________.

Most ________ are necessary for enzyme function.

What is the main water source for land plants?

Critical Thinking Questions

What type of plant problems result from nitrogen and calcium deficiencies?

Deficiencies in these nutrients could result in stunted growth, slow growth, and chlorosis.

Research the life of Jan Babtista van Helmont. What did the van Helmont experiment show?

van Helmont showed that plants do not consume soil, which is correct. He also thought that plant growth and increased weight resulted from the intake of water, a conclusion that has since been disproven.

List two essential macronutrients and two essential micro nutrients.

Answers may vary. Essential macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Essential micronutrients include iron, manganese, boron, molybdenum, copper, zinc, chlorine, nickel, cobalt, sodium, and silicon.

Glossary


Plant essential nutrients

Scientists have identified 16 essential nutrients and grouped them according to the relative amount of each that plants need:

  • Primary nutrients, also known as macronutrients, are those usually required in the largest amounts. They are carbon, hydrogen, nitrogen, oxygen, phosphorus, and potassium.
  • Secondary nutrients are those usually needed in moderate amounts compared to the primary essential nutrients. The secondary nutrients are calcium, magnesium, and sulfur.
  • Micro- or trace nutrients are required in tiny amounts compared to primary or secondary nutrients. Micronutrients are boron, chlorine, copper, iron, manganese, molybdenum, and zinc.

A very few plants need five other nutrients: cobalt, nickel, silicon, sodium, and vanadium.

Each essential nutrient affects specific functions of plant growth and development (Table 1). Plant growth is limited by the nutrient that is in the shortest supply (Fig. 1).


What Do These Nutrients Do? Let’s Break It Down By Nutrient

1. Nitrogen: Nitrate (the form of nitrogen that plants use) helps foliage grow strong by affecting the plant’s leaf development. It is also responsible for giving plants their green coloring by helping with chlorophyll production (gardensalive.com). For additional information on nitrogen, visit this blog: Nitrogen Fertilizers 101.

2. Phosphorus: Phosphorus is responsible for assisting with the growth of roots and flowers. Phosphorus also helps plants withstand environmental stress and harsh winters (gardensalive.com). For additional information on phosphorus, visit this blog article: Why Your Plants Need Phosphorus.

3. Potassium: Potassium strengthens plants, contributes to early growth and helps retain water. It also affects the plant’s disease and insect suppression (extension.uum.edu).

4. Magnesium: Magnesium contributes to the green coloring of plants (gardeningknowhow.com).

5. Sulfur: Sulfur helps plants resist disease as well as contributing the plant growth and the formation of seeds. They also aid in the production of amino acids, proteins, enzymes and vitamins (davesgarden.com).

6. Calcium: Calcium aids in the growth and development of cell walls. This is key because well-developed cell walls help the plant resist disease. It is also necessary for metabolism and the uptake of nitrogen by the plant (davesgarden.com).

How Do You Add These Nutrients To The Soil? Looking At Well-Balanced Fertilizers

One of the great things about the six essential nutrients is that they are easy to find.

Adding a well-balanced fertilizer is an easy way to increase nutrient levels in the soil. Be sure to check out Holganix's fertilizer options including: Holganix Blue Sky 21-0-0, Holganix 2-10-20 and Holganix granular options.

Unlocking Nutrients In The Soil

Healthy soil is already pumped with these nutrients, although some like nitrogen and phosphorus are often locked in an unusable form for the plant.

Plant and soil probiotics contains ACTIVE, beneficial microorganisms that unlock plant nutrients in the soil. They also nurture longer, more web-like root systems that are better able to mine for nutrients deeper in the soil.

Using Microbes To Improve Soil Health

Holganix Bio 800 + charges soil with over 800 species of soil microbes to improve plant performance. What does that mean for you?

That means you build soil and root health, adding the benefits of better soil structure to whatever soil type you have. This translates to improved yield on crops, better playability on golf courses and a reduced need for fertilizers and pesticides on lawns.

Download our ingredient list below to learn more about the soil microbes in Holganix Bio 800 +


Systemic Therapy for Colon Cancer

Bevacizumab and Angiogenesis

Angiogenesis delivers essential nutrients and oxygen for the sustained growth and metastasis in tumors and presents a rational target in cancer therapy. 93 These tumor-induced blood vessels are often structurally and functionally abnormal, impairing the effective delivery of chemotherapeutic agents to the cancer. 94 The abnormal process is thought to be driven by an imbalance of pro- and antiangiogenic factors, and disrupting the process by neutralizing vascular endothelial growth factor, a key ligand for angiogenesis, has been a focus in colorectal cancer therapy. 95

Bevacizumab is a humanized recombinant monoclonal antibody that binds vascular endothelial growth factor and inhibits liganddependent angiogenesis. The drug's efficacy was demonstrated in two randomized controlled trials, which led to FDA approval for use with any intravenous 5-FU-containing regimen in first- or second-line metastatic colorectal cancer therapy. 96 Several mechanisms have been speculated to explain the activity of bevacizumab and other antiangiogenic agents, including starving the tumor of essential nutrients and oxygen by inhibition of formation of tumor vasculature, and improving the delivery of chemotherapeutic agents by normalizing the tumor vasculature and decreasing interstitial pressures in tumors.

In a small randomized phase II trial, 104 patients were randomized to receive weekly bolus 5-FU and leucovorin (5-FU/LV) (control arm), bevacizumab 5 mg/kg or 10 mg/kg plus 5-FU/LV (low-dose and high-dose bevacizumab arms, respectively). 97 Compared with those in the control arm, patients in both bevacizumab arms had better response rate (control 17% low-dose 40%, high-dose 24%), longer median TTP (5.2, 9.0, and 7.2 months, respectively), and longer median survival (13.8, 21.5, and 16.1 months, respectively). It is interesting that the low-dose bevacizumab arm seemed to be superior to the high-dose arm and was partly attributed to some imbalance in randomization, resulting in more patients with poor prognostic factors in the latter group. The dose of 5 mg/kg for bevacizumab was thus chosen for the subsequent phase III trial. Bleeding (gastrointestinal and epistaxis), hypertension, thrombosis, and proteinuria were more common in the bevacizumab arms.

In the interim, irinotecan plus bolus 5-FU and leucovorin (IFL) became the standard first-line therapy for metastatic colorectal cancer in the United States (see earlier). As such, the subsequent phase III trial used IFL as the control regimen, and 813 patients with previously untreated metastatic colorectal cancer were randomized to IFL plus placebo, IFL plus bevacizumab 5 mg/kg, and 5-FU/LV plus bevacizumab 5 mg/kg. 98 The 5-FU/LV/bevacizumab arm was discontinued during a planned interim analysis when the data monitoring committee found that the addition of bevacizumab to IFL had an acceptable safety profile. The intention-to-treat analysis showed a superior median survival for the IFL plus bevacizumab arm compared with the control arm (20.3 versus 15.6 months P < .001) ( Fig. 15-4 ). The study arm also had a better response rate (44.8% versus 34.8% P = .004) and median duration of response (10.4 versus 7.1 months P = .001). Reversible hypertension and proteinuria were more frequent in the study arm. Other rare but serious adverse events included thrombotic events, gastrointestinal perforation (1.5% of the patients in the bevacizumab arm) and wound dehiscence.

The role of bevacizumab with oxaliplatin-based regimen for second-line therapy for patients with metastatic colorectal cancer was studied in a randomized phase III study (E3200). 99 In the study, previously treated patients were randomly assigned to FOLFOX4 alone or FOLFOX4 plus high-dose bevacizumab (10 mg/kg). Analysis of 829 patients showed superior median survival in the bevacizumab plus FOLFOX4 arm (12.9 versus 10.8 months P = .001). Dose reduction of bevacizumab to 5 mg/kg was allowed in the study for hypertension, bleeding, thrombosis, proteinuria, and abnormal liver tests. About 56% of 240 patients in the FOLFOX4 plus bevacizumab had bevacizumab dose reduction, and the overall survival was not statistically different from the group without dose reduction. 100

Despite the clear role of bevacizumab with intravenous 5-FU-based regimens in first- and second-line therapy for patients with metastatic colorectal cancer, more clinical questions still need to be clarified, such as efficacy of continuing bevacizumab into second-line therapy and synergism with oral fluoropyrimidines. Studies addressing the combination of bevacizumab and cetuximab are ongoing. In the BOND (Bowel Oncology with Cetuximab Antibody)-2 trial, 101 patients with advanced colorectal cancer who had unsuccessful irinotecan-based therapy, more than 80% of whom had also been pretreated with oxaliplatin, were enrolled in a randomized phase II trial comparing cetuximab plus bevacizumab with cetuximab/bevacizumab plus irinotecan as salvage therapy. The primary objective of the trial was to document the feasibility of the dual-antibody combinations and to assess the response rate in both arms. In terms of the first objective, no unexpected adverse effects were encountered when cetuximab and bevacizumab were combined the combination was feasible. Moreover, the addition of bevacizumab appeared to enhance the efficacy of cetuximab and cetuximab/irinotecan in terms of response rate, but more strikingly, in terms of time to tumor progression (TTP). This effect is even more noteworthy, since cetuximab monotherapy in BOND-1 was only associated with a rather disappointing median TTP of 1.5 months. Combining cetuximab with bevacizumab increased median TTP dramatically to 6.9 months. A similar effect was seen in the cetuximab + bevacizumab + irinotecan arm. Unfortunately, large clinical trials have indicated that “double biologic” strategies are harmful to patients.

With the latter data showing the feasibility of irinotecan with bevacizumab and cetuximab, several trials have investigated the combinations in first-line conventional chemotherapy and monoclonal antibodies. 102–104 In a randomized phase III trial of chemotherapy/bevacizumab with or without panitumumab (PACCE Study), median PFS in the experimental arm with both the biologics was 10 versus 11.4 months in the experimental versus control arms, respectively, and overall survival was 19.4 versus 24.5 months, also favoring the control arm. 102 The combination was inferior even in K-ras wild-type patients with more death rates and excess toxicity. The results are the same with another large study including cetuximab and bevacizumab (CAIRO 2 Study). 103 In this study, the combination of capecitabine/oxaliplatin/bevacizumab chemotherapy, with or without cetuximab, was tested in 755 untreated metastatic colorectal cancer patients. The primary endpoint was PFS. The study demonstrated worsened PFS in the double biologic arm, 10.7 in the control arm, and 9.5 in the experimental arm (P = .01). The quality-of-life scores were worse and toxicities also more common in the experimental arm. In the subset analysis, even patients with wild-type K-ras also did not benefit.

Most double-biologic arms of ongoing studies were closed based on the latter results, and such combinations should not be used outside of a clinical trial. The CALGB/Southwest Oncology Group Intergroup 80405, a phase III intergroup trial comparing FOLFOX or FOLFIRI-based chemotherapy (investigators' choice) with bevacizumab, cetuximab or both was also evaluating the role of double biologics. This trial has been amended now to include patients with K-ras wild-type only.