Environmental Engineering Reference
In-Depth Information
(Draper and Crosby
1981
; Zepp et al.
1992
; Wang et al.
2001
; White et al.
2003
;
Nakatani et al.
2007
; Vione et al.
2006
,
2009a
,
b
).
3.6 Occurence of H
2
O
2
and its Effect on Photosynthesis
In support of the involvement of H
2
O
2
in the photosynthetic reaction, several
H
2
O
2
-related phenomena have been observed in natural waters, which can be clas-
sified as follows (Mostofa et al.
2009
). First, the correlation between carbon pro-
duction and photolytically formed H
2
O
2
concentration, suggesting a link between
hydrogen peroxide and organic matter photosynthesis in lake water (Anesio et al.
2005
). Second, Chl
a
production in the epilimnetic layer (5-10 m) is typically
observed to increase with a decrease in total CO
2
contents (Talling
2006
), sug-
gesting that photosynthesis is highest at the epilimnetic layer (5-10 m) than in
the uppermost epilimnion (0-1 m). Correspondingly, the O
2
and Chl
a
contents
reach a minimum when the water temperature become highest during the summer
stratification period (Talling
2006
), suggesting that photoinduced degradation or
assimilation of Chl
a
may be responsible for the decrease in Chl
a
at the upper-
most layer. Here O
2
may be involved in the production of free radicals (H
2
O
2
or
HO
•
) that could inhibit photosynthesis (Mostofa and Sakugawa
2009
; Moffett and
Zafiriou
1990
). This result is similar to earlier studies where photosynthesis was
observed to be less effective in the uppermost layer (1 m) compared to the subse-
quent epilimnion (3 m) (Nozaki et al.
2002
). A ratio of variable to maximal fluo-
rescence (Fv/Fm) of phytoplankton productivity showed a decrease as irradiance
increased during the morning and an increase as irradiance declined in the after-
noon. These results may be associated with both photoprotective strategies in the
antennae of PSII and photo damage of PSII reaction centers (Zhang et al.
2008
).
Conversely, H
2
O
2
usually increases gradually starting in the morning, reaches a
maximum at noon and then gradually decreases in the afternoon (Mostofa and
Sakugawa
2009
). It is therefore suggested that high production of H
2
O
2
and sub-
sequent photoinduced generation of HO
•
at noon is susceptible to damage the PSII
reaction centers.
Third, H
2
O
2
may be concentrated by particulate organic matter or small fungi
through rapid transpiration (Komissarov
1994
,
1995
,
2003
). This hypothesis
can be supported by observation of relatively low production of H
2
O
2
in unfil-
tered samples compared to filtered ones during irradiation (Moffett and Zafiriou
1990
; Cooper et al.
1988
; Petasne and Zika
1997
). An increase in the growth rate
of plants and mycelial fungi is detected when the H
2
O
2
concentration increases
up to an optimum level, from 1 nM to 10 M, and the growth rate decreases when
H
2
O
2
approaches 1 mM (Komissarov
2003
; Ivanova et al.
2005
). High levels of
H
2
O
2
may photolytically produce HO
•
, a strong oxidizing agent, that may cause
ecophysiological disorders in plants, decrease the CO
2
assimilation rate and
affect stomatal conductance, fluorescence and needle life span (Kume et al.
2000
;
Kobayashi et al.
2002
). In natural waters, HO
•
that is produced photolytically from