Environmental Engineering Reference
In-Depth Information
are effective in inhibiting O
2
evolution and PSII activity of microorganisms. The
inhibitory effect on PSII is often increased with increasing concentration of toxic
compounds. Levofloxacin hydrochloride, one of the most commonly used fluo-
roquinolone antibiotics, can decrease the density of the active photosynthetic
reaction centers of
Synechocystis
sp., inhibit electron transport, and increase the
dissipated energy flux per reaction center. All these effects together are able to
decrease the photosynthetic efficiency (Pan et al.
2009
).
The adverse effect on photosynthesis is thought to be caused by two facts.
First, the molecular structures of organic contaminants are mostly composed of
N-, S-, O-, and/or P-containing functional groups, which are susceptible to form
H-bonding with the functional groups of PSII. This effect can decrease the effi-
ciency of electron release from PSII. It has in fact been demonstrated that the her-
bicide DCMU can directly block the electron transport in PSII (Berden-Zrimec
et al.
2007
; Tissut et al.
1987
; Behrenfeld et al.
1998
). The second issue is that N-,
S-, O-, or P-containing functional groups can release electrons upon excitation by
light, which can produce ROS such as O
2
•
−
, H
2
O
2
and HO
•
. These oxidizing spe-
cies can damage the PSII system, thereby reducing the photosynthetic efficiency as
a whole.
KCN (an inhibitor of mitochondrial respiration) and 3-(3,4-dichlorophenyl)-
1,1-dimethylurea (an inhibitor of photosynthesis) had no significant effects on
ROS production. In contrast, vitamin K3 (a plasma membrane electron shuttle)
can enhance ROS production and its antagonist, dicumarol, can decrease it (Liu
et al.
2007
). Photosynthetic organisms can produce ROS by activating various oxi-
dases and peroxidases, in response to environmental stresses such as pathogens,
drought, light intensity, an increase in temperature from 7 °C to 30 °C, and con-
taminants such as paraquat (Peng and Kuc
1992
; Moran et al.
1994
; Karpinski
et al.
1997
; Iturbe-Ormaetxe et al.
1998
; Twiner and Trick
2000
).
5.10 Effect of Size-Fractionated Phytoplankton
Planktonic algae of <5
μ
m in size are major fixers of inorganic carbon in the ocean
and dominate phytoplankton biomass in post-bloom, stratified oceanic temperate
waters (Li
1994
; Tarran et al.
2001
). Large and small algae are viewed as having
a critical growth dependence on inorganic nutrients. The latter can be assimilated
at lower ambient concentrations due to the higher surface-area-to-volume ratios
of small vs. larger organisms (Malone
1980
; Chisholm
1992
; Zubkov and Tarran
2008
). Experimental studies that adopted phosphate tracer suggest that small algae
can uptake inorganic phosphate indirectly, possibly through feeding on bacterio-
plankton (Hansen and Hjorth
2002
; Stibor and Sommer
2003
; Tittel et al.
2003
;
Unrein et al.
2007
; Zubkov et al.
2007
; Jones
2000
; Bird and Kalff
1986
; Arenovski
et al.
1995
; Rothhaupt
1996
; Thingstad et al.
1996
; Caron
2000
). Inorganic phos-
phate and other nutrients (e.g. NO
3
−
) can originate mostly from two processes:
(i) photoinduced and microbial assimilations of algae (or cyanobacteria), and (ii)
