612
K. M. G. Mostofa et al.
1992). Some desiccation-tolerant cells accumulate large amounts of the disaccharides trehalose and/or sucrose. Of these, mostly trehalose can prevent damage
from dehydration, not only by inhibiting fusion between adjacent membrane vesicles 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 superoxide 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 various 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 significantly enhance the sudden growth of plants all over the world at the beginning 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 production 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 μM, see chapter
“Photoinduced and Microbial Generation of Hydrogen Peroxide and Organic
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 photosynthesis ( Komissarov 1995, 2003; Mostofa et al. 2009). However, high concentrations 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 mechanisms 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
− , NO 3
− and PO 4
3− ) and various photo- and microbial products, such as H 2 O 2 , CO 2 , DIC, LMW DOM, and so on (see also chapters “Dissolved Organic Matter in Natural Waters”, “Photoinduced and Microbial
Degradation of Dissolved Organic Matter in Natural Waters”, “Chlorophylls
and Their Degradation in Nature”, and “Impacts of Global Warming on
K. M. G. Mostofa et al.
1992). Some desiccation-tolerant cells accumulate large amounts of the disaccharides trehalose and/or sucrose. Of these, mostly trehalose can prevent damage
from dehydration, not only by inhibiting fusion between adjacent membrane vesicles 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 superoxide 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 various 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 significantly enhance the sudden growth of plants all over the world at the beginning 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 production 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 μM, see chapter
“Photoinduced and Microbial Generation of Hydrogen Peroxide and Organic
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 photosynthesis ( Komissarov 1995, 2003; Mostofa et al. 2009). However, high concentrations 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 mechanisms 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
− , NO 3
− and PO 4
3− ) and various photo- and microbial products, such as H 2 O 2 , CO 2 , DIC, LMW DOM, and so on (see also chapters “Dissolved Organic Matter in Natural Waters”, “Photoinduced and Microbial
Degradation of Dissolved Organic Matter in Natural Waters”, “Chlorophylls
and Their Degradation in Nature”, and “Impacts of Global Warming on