Photosynthesis in Nature: A New Look - Photobiogeochemistry of Organic Matter - page 615

and PO 4 3 − ) are mostly released dur-
ing photoinduced and microbial assimilation or respiration of algal/phytoplankton
biomass (Mostofa et al. 2011 ; Kopá ˇek et al. 2003 ; Li et al. 2008 ; Mallet et al.
1998 ; Carrillo et al. 2002 ; Lehmann et al. 2004 ; Fu et al. 2005 ). (ii) Formation
of N-containing (NH 4

− − +

follows: (i) Nutrients (NO 3 , NO 2 , NH 4

) and P-containing inorganic compounds (PO 4 3 − )
typically occurs upon degradation of dissolved organic nitrogen (DON) and dis-
solved organic phosphorus (DOP) in natural waters (Mostofa et al. 2011 ; Kim
et al. 2006 ; Li et al. 2008 ; Bronk 2002 ; Zhang et al. 2004 ; Vähätalo and Järvinen
2007 ; Haaber and Middelboe 2009 ). The degradation of Phaeocystis pouchetii
lysates is associated with significant regeneration of inorganic N and P and
produces 148 g N L − 1 and 7 g P L − 1 , which corresponds to 78 % and 26 % of
lysate N and P being mineralized to NH 4

+ −

or NO 2

and PO 4 3 − , respectively (Haaber and
Middelboe 2009 ). Contribution of nutrients through viral lysis might be an impor-
tant mechanism that promotes heterotrophic nutrient cycling and stimulates pri-
mary production (Haaber and Middelboe 2009 , 2008 ; Brussaard et al. 2008 ).
(iii) NO 3

+

− −

and NO 2 can be regenerated by oxidation of ammonia in nitrifica-

+ 2H + + H 2 O) and of dissolved organic nitrogen
(DON) in lake waters (Lehmann et al. 2004 ; Mack and Bolton 1999 ; Kopá ˇek et
al. 2004 ; Minero et al. 2007 ). (iv) NO 2

+ −

tion (NH 4 + 2O 2 → NO 3

− −

are preferentially detected in
epilimnetic water rather than the hypolimnion (Mostofa KMG et al., unpublished
data; Kim et al. 2006 ; Li et al. 2008 ; Lehmann et al. 2004 ; Kopá ˇek et al. 2004 ;
Minero et al. 2007 ), and they are also involved in photoinduced generation of HO

and NO 3

•

that is able to degrade DOM in the epilimnion (see also chapters “ Photoinduced
Generation of Hydroxyl Radical in Natural Waters ” and “ Photoinduced and
Microbial Degradation of Dissolved Organic Matter in Natural Waters ”) (Mostofa
et al. 2009 ; Nakatani et al. 2007 ; Takeda et al. 2004 ; Zellner et al. 1990 ; Mopper
and Zhou 1990 ). Furthermore, the NO 2

−

ion is generally observed at low concen-
tration during the summer season (Mostofa KMG et al., unpublished data; Kim et
al. 2006 ; Li et al. 2008 ), and possibly it is photolytically more active in production
of HO

•

−

(see also chapters “ Photoinduced Generation of Hydroxyl
Radical in Natural Waters ” and “ Photoinduced and Microbial Degradation of
Dissolved Organic Matter in Natural Waters ” ). It is also a rather photolabile
compound in surface waters, undergoing faster direct photolysis in lake than in
ultrapure water. This effect is linked to the scavenging of photogenerated tran-
sients by DOM, which finally prevents the recombination of photogenerated, tran-
sient nitrogen species back into nitrite (Vione et al. 2009a ).
Primary production or Chl a often increases with increasing total phosphorus
(TP) and nutrients, suggesting that uptake of P and nutrients takes place during
primary production (Doyle et al. 2005 ; Huszar et al. 2006 ; Nõges et al. 2008 ;
McCarthy et al. 2009 ; Mohlin and Wulff 2009 ; Guildford and Hecky 2000 ;
Lehmann et al. 2004 ; Schindler 1974 , 2006 ; Havens et al. 1995 ; Smith et al.
1995 ). Chl a is significantly correlated with total P in marine environments, but
total P concentration in marine sites is relatively higher compared to freshwater
(Guildford and Hecky 2000 ). Uptake of phosphorus during phytoplankton growth
is greatly stimulated in presence of humic substances, but the phosphate uptake is

than in NO 3