N Fertilization Dependent Bacterial and Archaeal …
65
causing low oxidation—reduction potential. The intermittent change of redox potential (Eh) is a unique character, which vary from −200 to −300 mV to + 500 to +
700 mV. Reduced environment with an Eh of—250 mV is prevalent after flooding
when the soil pores are filled with water and free oxygen replacing air and soil
environments. Alternate wetting and drying process encourages change in pH and
are influenced by type of cations, water contents and concentration of neutral salts.
The variation in both pH and Eh approves changes in redox sensitive components
like iron, manganese, sulfur, carbon and nitrogen [78]. The reaction curtails oxygen
supply furthermore and results in death of aerobic organisms and proliferation of
facultative anaerobes. They are in turn proceeded by series of reduction process and
the reducing elements in the order of O 2 , NO 3 , MnO 2 and Fe (OH) 3 -Fe
2+ resulting
in reduced counterparts namely Fe(II), Mn(II),NH 4 along with an array of unstable
organic components [72]. This also results in domination of facultative microbes
followed by anaerobic microorganisms consequently using oxidized soil substrate
as electron acceptors.
1.2 Zones of Wetland
The assorted soil-water lowland system comprises of three zones viz., surface (oxic),
anoxic and rhizosphere which harbor indigenous microbial community with its own
unique biological activities respectively [69]. The zone surrounding the plant roots
gets accustomed to submerged soils and develops process ensuring oxygen and other
gas exchange mainly through aerenchyma tissues. The porous aerenchyma enables
root respiration where most of the oxygen is consumed and escaped oxygen oxidizes
the reduced soil components surrounding them making thin aerobic zone characterized by high redox potential [95]. The oxic layer can further be differentiated
into floodwater and oxidized surface layer which are oxidized and partially oxidized
respectively. Oxidized surface layer is the water column superimposed on the anaerobic layer marked by dissolved oxygen and ranges from few mm to one cm in
thickness depending upon the O 2 utilization rate [32]. They are characterized with
higher redox potential encompassing aerobic microbial reactions like nitrification,
ammonification, and immobilization. They are also prone to pH fluctuations due
growth of algae which ensures removal of CO 2 . The anaerobic (anoxic) layer is
characterized by low redox potential, holds few cm thickness and are conducive
accumulation of ammonia [50]. Waterlogged cultivation of paddy supports anoxia in
most of soil compartments rendering a hotspot for methanogenenic microorganisms.
In addition, various N transformation reactions including N 2 fixation, N mineralization and immobilization, denitrification and dissimilatory nitrate reduction occurs.
Thus, anaerobic metabolism heads the role and their products formed marks distinct
from the arable soils.
65
causing low oxidation—reduction potential. The intermittent change of redox potential (Eh) is a unique character, which vary from −200 to −300 mV to + 500 to +
700 mV. Reduced environment with an Eh of—250 mV is prevalent after flooding
when the soil pores are filled with water and free oxygen replacing air and soil
environments. Alternate wetting and drying process encourages change in pH and
are influenced by type of cations, water contents and concentration of neutral salts.
The variation in both pH and Eh approves changes in redox sensitive components
like iron, manganese, sulfur, carbon and nitrogen [78]. The reaction curtails oxygen
supply furthermore and results in death of aerobic organisms and proliferation of
facultative anaerobes. They are in turn proceeded by series of reduction process and
the reducing elements in the order of O 2 , NO 3 , MnO 2 and Fe (OH) 3 -Fe
2+ resulting
in reduced counterparts namely Fe(II), Mn(II),NH 4 along with an array of unstable
organic components [72]. This also results in domination of facultative microbes
followed by anaerobic microorganisms consequently using oxidized soil substrate
as electron acceptors.
1.2 Zones of Wetland
The assorted soil-water lowland system comprises of three zones viz., surface (oxic),
anoxic and rhizosphere which harbor indigenous microbial community with its own
unique biological activities respectively [69]. The zone surrounding the plant roots
gets accustomed to submerged soils and develops process ensuring oxygen and other
gas exchange mainly through aerenchyma tissues. The porous aerenchyma enables
root respiration where most of the oxygen is consumed and escaped oxygen oxidizes
the reduced soil components surrounding them making thin aerobic zone characterized by high redox potential [95]. The oxic layer can further be differentiated
into floodwater and oxidized surface layer which are oxidized and partially oxidized
respectively. Oxidized surface layer is the water column superimposed on the anaerobic layer marked by dissolved oxygen and ranges from few mm to one cm in
thickness depending upon the O 2 utilization rate [32]. They are characterized with
higher redox potential encompassing aerobic microbial reactions like nitrification,
ammonification, and immobilization. They are also prone to pH fluctuations due
growth of algae which ensures removal of CO 2 . The anaerobic (anoxic) layer is
characterized by low redox potential, holds few cm thickness and are conducive
accumulation of ammonia [50]. Waterlogged cultivation of paddy supports anoxia in
most of soil compartments rendering a hotspot for methanogenenic microorganisms.
In addition, various N transformation reactions including N 2 fixation, N mineralization and immobilization, denitrification and dissimilatory nitrate reduction occurs.
Thus, anaerobic metabolism heads the role and their products formed marks distinct
from the arable soils.