Environmental Engineering Reference
In-Depth Information
1992
). Some desiccation-tolerant cells accumulate large amounts of the disac-
charides trehalose and/or sucrose. Of these, mostly trehalose can prevent damage
from dehydration, not only by inhibiting fusion between adjacent membrane ves-
icles during drying, but also by maintaining membrane lipids in the fluid phase
in the absence of water (Singh et al.
2002
; Crowe et al.
1987
,
1992
; Leslie et al.
1994
). Trehalose can depress the phase transition temperature of the dry lipids
after desiccation and maintain them in the liquid crystal state (Crowe et al.
1992
;
Leslie et al.
1994
). The increasing activities of catalase, peroxidase and super-
oxide dismutase and the level of proline can constitute a natural endogenous
defense system that increases the response to water stress (Fariduddin et al.
2009
;
Schützendübel and Polle
2002
).
Rainfall can greatly increase photosynthesis, particularly by increasing vari-
ous physiological phenomena such as leaf water potential, net photosynthetic
rate, stomatal conductance, and transpiration (Souch and Stephens
1998
; Smit
and Rethman
2000
; Morris et al.
2004
; Li et al.
2007
). Moreover, it can sig-
nificantly enhance the sudden growth of plants all over the world at the begin-
ning of summer season and at the end of winter season. The consequence is an
increase of annual biomass production and a simultaneous increase of the pro-
duction of various food and crops. Maximum photoinduced efficiency of PSII is
significantly increased with an increase in rainfall (Li et al.
2007
). Among other
issues, this might also be caused by the occurrence of H
2
O
2
and nutrients in rain
water. The supply of exogenous H
2
O
2
from rainfall (up to 200
μ
M, see chapter
Peroxides in Natural Waters
”) could enhance photosynthesis and make PSII reach
its maximum photoinduced efficiency. On the other hand, leaf wetness causes not
only instantaneous suppression of photosynthesis but also chronic damage to the
photosynthetic apparatus (Ishibashi and Terashima
1995
). Interestingly, a direct
link has been observed between rainwater H
2
O
2
content and the rate of photosyn-
thesis ( Komissarov
1995
,
2003
; Mostofa et al.
2009
). However, high concentra-
tions of H
2
O
2
(50-100 M) in the presence of iron (Fe) and oxalate can generate
HO
•
that would decrease plant productivity and growth (Kobayashi et al.
2002
).
In the case of aquatic microorganisms, drought stress or absence of rainfall for
a longer period can significantly affect photosynthesis. In this case, similar mecha-
nisms are followed as for high light irradiance as explained in the earlier section.
5.5 Effects of the Contents and Nature of DOM and POM
Organic matter (OM) consisting of DOM and POM is one of the key factors that
can produce nutrients (NO
2
and PO
4
3
−
) and various photo- and micro-
bial products, such as H
2
O
2
, CO
2
, DIC, LMW DOM, and so on (see also chap-
−
−
, NO
3
