Guide to the Planted Aquarium, Part II – Nutrients and Nutrient Supplementation
Phil Edwards, MS
Phil Edwards, MS
This is the second part in the multi-part series "Guide to the Planted Aquarium" In this part the author will discuss the various inorganic nutrients (hereafter, nutrients) needed by plants and their main functions in plant biochemistry. Definitions of terms used in this section can be found in Part I. This section is not intended as a discussion of which source of nutrients, dry chemicals or commercially available solutions, is superior to the other. Any mention of commercially available solutions is included strictly for completeness. It is up to the individual aquarist to choose which source is best for his or her own needs and desires.
Please refer to Part I for definitions and explanations of terms contained herein- http://www.plantedtank.net/forums/8.../1133146-beginners-guide-planted-aquaria.html
Author's Note: Images will be added as needed once permission is granted by the image's owner.
Part II, Section I- Common Sources of Nutrients and Generally Accepted Ranges of Concentration
Commonly used sources of nutrients in dry form:
C: CO2 gas
N: potassium nitrate (KNO3)
P: potassium phosphate (KH2PO4)
K: potassium sulfate (K2SO4)
Ca: calcium chloride (CaCl2) and calcium sulfate dihydrate (CaSO4 * 2H2O)
Mg: magnesium chloride (MgCl2) and Epsom salts (MgSO4 * 7H2O)
S: calcium sulfate dihydrate (CaSO4 * 2H2O) and Epsom salts (MgSO4 * 7H2O)
Fe: chelated iron (ferrous gluconate, FeEDTA, FeDPTA)
Minor and trace elements: commercially available mixes
All of the above are available as liquid solutions.
Currently accepted best practice concentration ranges for each nutrient:
CO2: 20-30 ppm
N03: 10-20 ppm
P04: 0.5-2 ppm
K: 10-20 ppm
Ca: 10-30 ppm
Mg: 2-5 ppm
S: Generally considered to be sufficiently added as part of Epsom salts and/or calcium sulfate
Fe: 0.1 ppm
Author's Note: These are the generally accepted concentration ranges for use in systems with moderate to high light input and which receive the majority of nutrient input from the water column. Plants in aquariums with soil amended substrates "Walstad" or "MTS" receive the majority of their nutrients from the substrate; therefore, maintaining water column concentrations of N, P, and Fe as above is not typically required. Based on the author's research, maintaining the above concentrations of K, Ca, and Mg is recommended, but not strictly necessary.
Part II, Section II- Nutrient FunctionPlant Physiology and Development, 5th Edition, Taiz and Zeiger (Sinauer assoc) was used for fact-checking and as a general reference for this section. Specific citations are listed where appropriate.
This section will only cover the eight main nutrients which are commonly discussed in the hobby: C, N, P, K, Ca, Mg, S, and Fe. Discussion of the remaining minor and trace elements can be summarized as their necessity in general biochemical reactions and functions.
Primary Macronutrient "macros"- Elements (C, N, P, K) needed by plants in large amounts to sustain life and build and maintain tissues. Carbon is typically omitted from the list as it is assumed by terrestrial horticulturists that plants have unlimited access to atmospheric CO2. In planted aquariums C must be supplemented by some means and as such the author has included it in the list of macros to be added.
Carbon (C)- Carbon is the basis of all life on Earth currently known to science. All organisms depend on it to make the organic compounds required for existence. Unlike many animals which create skeletons out of Ca, Mg, and other materials, plants use carbohydrates to create their structure (structural carbohydrate). Two of the most common structural carbohydrates are cellulose and lignin.
One of the unique traits of plants and other photosynthetic organisms is the use of two major systems for the acquisition of energy; the light (light dependent) and dark (light independent) cycles. While plants are receiving light they make the molecules ATP and NADPH in Photosystems 1 and 2. These molecules are then used in the dark cycle to provide the energy needed to produce glucose. From that point plants then either use glucose for respiration or as a source of organic carbon to synthesize amino acids, proteins, enzymes, structural carbohydrates, photosynthetic pigments, and other organic compounds.
Multiple carbon supplementation options are available for planted aquarium hobbyists; CO2 gas and liquid carbon sources. The two most common sources of CO2 are pressurized gas and as a biproduct of fermentation aka "DIY". In the past DIY yeast reactors were relatively common source of CO2 as pressurized gas was considered risky due to "End of Tank Dump" which could potentially kill fish. In recent years an increasing number of aquarium supply companies have released yeast reactor kits catering to aquarists who do not wish to make their own or to aquarists who aren't familiar with how to make their own. Use of pressurized gas has become increasingly popular as high quality plant-specific regulators and small injection systems based on low pressure canisters have become available. Since plants have evolved to use CO2 as their primary source of C, gas injection is considered by many to be superior to liquid carbon sources.
While not as popular or well-regarded as they were in the past, liquid carbon products remain a viable source of C for the planted aquarist. Much discussion has centered around the mechanisms by which these products supply C and their true effectiveness as a carbon source. The author has had the opportunity to speak with some suppliers of liquid carbon sources and was told that the products concerned supply either photosynthetic intermediates or molecules used in energy producing metabolic cycles.
Nitrogen (N)- Nitrogen is perhaps the second most used element after carbon. Four N are bound to one Mg to form the center of chlorophyll. It is an essential component of amino acids and thereby all proteins which organisms use to build cellular structure, synthesize genetic material, and in a host of biochemical reactions. Plant scientists have determined that the most energetically favorable forms of N are ammonia and ammonium (NH3/NH4+) whereas nitrate (NO3-) is easier to store due to NH3/NH4+ being toxic at high concentrations.
Phosphorus (P)- Phosphorus is the third of the four macronutrients. Mentioned above, the ATP and NADP molecules used in the light and dark cycles both contain phosphate (PO43-) making P an essential element in energy acquisition and transport. In addition, P is a central element in the phospholipid bilayer found in all cells. This layer plays an important role in maintaining concentrations of water soluble compounds and ions within the cell. Lastly, P is a major component of nucleic acids which control cell division and growth of new tissue.
Potassium (K)- Potassium plays general, but important, roles in osmotic regulation, ionic transport, enzyme activation, and opening/closing of stomata. Of particular note in submerged plants are the roles K plays in activating ATP production enzymes and osmotic regulation. As submerged plants aren't able to take advantage of evaporation to facilitate nutrient transport they must take advantage of osmosis to move nutrient and energy laden solutions throughout their bodies. One way which they accomplish this is transporting K into cells which creates a difference in solute concentration (osmotic gradient), causing water to move toward that concentration in order to dilute the solute and return to a state of solute equilibrium. In emergent culture this same mechanism is used to open and close stomata to regulate atmospheric CO2 aquisition. The author speculates that opening and closing of stomata is a means of regulating oxygen concentration in submergent culture, resulting in pearling.
Calcium (Ca)- Like potassium, calcium plays a general role in plant life. Perhaps the most important of these is as calcium pectate, a material which strengthens cell walls, promotes structural integrity, and aids in cell elongation. (Hanson, 1984) observed that plants cultured in solutions with low Ca concentrations demonstrated leakage of ions and metabolites.
Magnesium (Mg)- Previously mentioned, Mg is the central element in the ring structure of Chlorophyll. It is also used as an enzyme activator and is important to ATP utilization where ATP must be bound to Mg to be used.
Sulfur (S)- The main role of S in plant life is primarily as an activator or enabler of protein, lipid, and enzyme synthesis as well as chlorophyll production.
Iron (Fe)- Iron's main role in plant biology is in chlorophyll synthesis. While not a component of chlorophyll itself it is an essential part of the process. SL353/SS555: Iron (Fe) Nutrition of Plants