Boron occurs in nature exclusively in the form of boron compounds. With an average molar
concentration of 4,16.10-4 mol/l, boron is the eighth most common element in marine
water. Expressed in mass units its average concentration is 4,5.10-3 g/l (4,5
mg/l).
Version 2012-III
Boron - (Borum) - B
Boron occurs in
nature exclusively in the form of boron compounds. With an average
molar concentration of 4,16.10-4 mol/l, boron is the eighth most
common element in marine water. Expressed in mass units its average
concentration is 4,5.10-3 g/l (4,5 mg/l).
Occurrence
Boron occurs in marine water in two equally represented forms (H3BO3
- Boric acid and B(OH)4-). Although not widely known, boron’s contribution
to the buffer capacity of marine water is surpassed only by that of carbon.
Contribution to the buffer capacity of marine water:
94% Carbon – HCO3-,
CO32-
5% Boron – B(OH)4-
1% Ostatní
Biogenous role
Current knowledge regarding boron reconfirms the conclusion that
it plays an essential biogenous role; nevertheless the exact mechanisms
are still not fully understood. A series of experiments was performed on
cyanobacteria to study the effect of the boron concentration on the fixation
of atmospheric nitrogen. The observed inhibition of the activity of the
nitrogenase enzyme, as well as of the growth for certain cyanobacteria
species (Nodularia sp., Chlorogloeopsis sp., Nostoc sp.) was ascribed to
the absence of boron. The evidence shows that the boron absence leads to
negative changes in the morphology of heterocyst - specialised cells, essential
for the organic fixation of atmospheric nitrogen.
Cyanobacteria, also known as blue-green algae, produce their own strain
through photosynthesis. They can live overland as well as in the oceans,
where they participate in the nitrogen ocean cycle. Some cyanobacteria
species co-exist in coral cells with Zooxanthellae, where they produce
the nitrogenase enzyme.
Thanks to its capability to reduce the triple nitrogen bond, this enzyme
is widely used for nitrogen fixation - it is the only way to a regressive
use of molecular (atmospheric or diluted in marine water) nitrogen for
live organisms. Cyanobacteria, as well as other bacteria, enter this process
as symbionts, since the large majority of plants and animals do not possess
the capability of fixing molecular nitrogen themselves. In order for the
bacteria to produce nitrogenase, the presence of certain trace elements
is essential, as for instance iron and molybdenum.
Further studies were carried out to determine the effect of concentration
changes of certain trace elements - among them also boron - on corallites.
The long-term test results showed clearly the direct relation between the
boron concentration and coral riff growth and in this manner also with
photosynthesis (Zooxanthellae, phytocysts). The maintenance of the right
boron concentration in tanks with primarily hard corals is therefore essential.
Summary
Occurrence in seawater:
H3BO3 a B(OH)4-
Recommended concentration:
4,5 mg/l (4,4 – 4,8 mg/l)
Influence on:
Alkalinity (buffering capacity); Invertebrates
Biogenous role:
Coral growth
Literature
An Introduction to the Chemistry of the Sea, Michael E. Q. Pilson, Pearson Education Boron Requirement in Cyanobacteria Its Possible Role in the Early Evolution of Photosynthetic Organisms. Ildefonso Bonilla , Mercedes Garcia-González , Pilar Mateo , Plant Physiol. 1990 Dec ;94 (4):1554-1560 16667889 Trace metals in corals--hind casting environmental chemical changes in the tropical Atlantic waters Holmes, C W, Koenig, A, Ridley, W I, Wilson, S A Eos Trans. AGU, 83(47), Fall Meet. Suppl., Abstract xxxxx-xx, 2002, GC21B-0157 Discovery of Symbiotic Nitrogen-Fixing Cyanobacteria in Corals Michael P. Lesser, Charles H. Mazel, Maxim Y. Gorbunov, Paul G. Falkowski
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