Environmental Engineering Reference
In-Depth Information
plants, bacteria and cyanobacteria. Cyanobacteria, in contrast to higher plants, are
well enriched with PSI as compared with PSII: the PSI/PSII ratio is about unity
in higher plants, but it is much higher in cyanobacteria, varying between 3 and
5.5 (Rakhimberdieva et al.
2001
). On the other hand, either PSI or PSII RCs are
used to convert light energy in anoxygenic photosynthesis, which typically occurs
in many bacteria. Anoxygenicphotosynthesis is a process where uptake of light
energy occurs without the release of O
2
. Anoxygenic species can utilize hydrogen
sulfide (H
2
S) or other species as sources of reductants, giving various forms of sul-
fur as by-products. It is noted that green bacteria can use H
2
S, while purple sulfur
bacteria (
Thiorhodaceae
) can use various reduced sulfur compounds including
Na
2
S
2
O
3
, Na
2
SO
3
, S and H
2
S, molecular hydrogen (H
2
) and organic substances
during photosynthesis (van Niel
1931
;
1936
; Roelofsen
1935
; Muller
1933
).
Anoxygenic species are mostly equipped with variety of bacteriochlorophylls.
The chlorophyll absorption bands at the red end of the spectrum are only of lim-
ited use in water ecosystems, because of the rapid attenuation of red light by water
(Kirk
1976
). Therefore, the ability of many cyanobacteria and aquatic higher plants
to photosynthesize and grow are markedly affected by the availability of blue light,
which is in turn highly dependent on the concentration of yellow substance within
water (Kirk
1976
). All natural waters generally contain a significant amount of yel-
low substances that absorb light in the blue and ultraviolet (Hutchinson
1957
; Kalle
1966
; Jerlov
1968
; Morel et al.
2007
). Yellow substances originate generally from
the occurrences of both allochthonous humic substances (fulvic and humic acids)
of terrestrial plant origin and autochthonous fulvic acids of algal or phytoplank-
ton origin, which absorb light in the blue and ultraviolet range (see also chapters
Matter in Natural Waters
”
) (Mostofa et al.
2009
; Mostofa et al.
2009
; Zhang et al.
2009
; Hutchinson
1957
; Kalle
1966
; Jerlov
1968
; Parlanti et al.
2000
).
2.1 Biogeochemical Functions of Photosynthesis
The different functions of photosynthesis can be summarized as follows: (i)
Photosynthetic oxygen production by cyanobacteria can lead to oxygenation of
the atmosphere and oceans, in turn allowing aerobic respiration and the evolu-
tion of large, complex and ultimately intelligent organisms (Catling et al.
2005
).
Oxygenic photosynthesis has evolved hundreds of millions of years before the
atmosphere became permanently oxygenated. Therefore, biogenic oxygen produc-
tion started very early in Earth's history, before the start of the geological record,
leading to an Archaean (greater than 2.5 Ga, gigaannum: 10
9
years) atmosphere
that was highly oxygenated (Ohmoto
1997
; Catling and Claire
2005
; Buick
2008
).
(ii) Photosynthesis is the only process that can balance the biosphere by convert-
ing atmospheric CO
2
into organic/biological matter, at the same time by releas-
ing O
2
into the atmosphere. (iii) All forms of life in the biosphere are dependent
on food and primarily on vegetables and terrestrial plants, the matter of which is
