6
mercially important tropical grasses. N 2 fixation in terrestrial ecosystems is a major
source of N with about 25% due to agriculture (Galloway et al. 2008). In natural
terrestrial environments, N 2 fixation is found in soils catalysed by free-living bacteria, bacteria that form loose associations with plant roots, and symbiotic bacteria
and cyanobacteria that form tight, sometimes endosymbiotic relationships with
multicellular plants on both their leaves and roots. Cyanobacteria are found associated with plant stems and in lichens. The soil matrix is very different in the
microscale distributions of nutrients and O 2 than the water column of aquatic environments. Because of the heterogeneity of soils, N limitation can occur, and microzones that are low in O 2 can facilitate N 2 fixation. In contrast, in the oceans and
activity, there are free-living and symbiotic N 2 -fixing microorganisms, many of
them cyanobacteria, associated with the unicellular algae, the “plants” of the oceans
which dominate oceanic primary production. There is also some N 2 fixation in
marine sediments catalysed by free-living bacteria and possibly Archaea, but at
relatively low rates due to the presence of fixed combined N which can repress the
synthesis and activity of nitrogenase. In some lakes, rivers and estuaries, low N
availability relative to phosphorus stimulates dense growth or blooms of N 2 -fixing
cyanobacteria, most often heterocyst-forming. N 2 fixation is important in the lownutrient oligotrophic regions of the open ocean. The magnitude of N 2 fixation in the
marine environment is difficult to quantify but is an important input and will be
discussed in detail in subsequent chapters.
References
Baas-Becking, L. G. M. (1934). Geobiologie; of inleiding tot de milieukunde. Den Haag: WP Van
Stockum & Zoon NV.
Barnard, R., Leadley, P. W., & Hungate, B. A. (2005). Global change, nitrification, and denitrification: A review. Global Biogeochemical Cycles, 19(1), 1–13.
Canfield, D. E., Glazer, A. N., & Falkowski, P. G. (2010). The evolution and future of Earth’s
nitrogen cycle. Science, 330(6001), 192–196.
Dworkin, M., & Gutnick, D. (2012). Sergei Winogradsky: A founder of modern microbiology and
the first microbial ecologist. FEMS Microbiology Reviews, 36(2), 364–379.
Falkowski, P. G. (2015). Life’s engines: How microbes made habitable (224 p.). Princeton:
Princeton University Press.
Falkowski, P. G., Fenchel, T., & Delong, E. F. (2008). The microbial engines that drive Earth’s
biogeochemical cycles. Science, 320(5879), 1034–1039.
Galloway, J., Dentener, F., Capone, D., Boyer, E., Howarth, R., et al. (2004). Nitrogen cycles: Past,
present and future. Biogeochemistry, 70, 153–226.
Galloway, J. N., Townsend, A. R., Erisman, J. W., Bekunda, M., Cai, Z., et al. (2008). Transformation
of the nitrogen cycle: Recent trends, questions, and potential solutions. Science, 320(5878),
889.
Gottschalk, G. (2012). Bacterial metabolism. New York: Springer.
Howard, J. B., & Rees, D. C. (1996). Structural basis of biological nitrogen fixation. Chemical
Reviews, 96, 2965–2982.
Moore, C., Mills, M., Arrigo, K., Berman-Frank, I., Bopp, L., et al. (2013). Processes and patterns
of oceanic nutrient limitation. Nature Geoscience, 6(9), 701–710.
1 Nitrogen Fixation in the Marine Environment
mercially important tropical grasses. N 2 fixation in terrestrial ecosystems is a major
source of N with about 25% due to agriculture (Galloway et al. 2008). In natural
terrestrial environments, N 2 fixation is found in soils catalysed by free-living bacteria, bacteria that form loose associations with plant roots, and symbiotic bacteria
and cyanobacteria that form tight, sometimes endosymbiotic relationships with
multicellular plants on both their leaves and roots. Cyanobacteria are found associated with plant stems and in lichens. The soil matrix is very different in the
microscale distributions of nutrients and O 2 than the water column of aquatic environments. Because of the heterogeneity of soils, N limitation can occur, and microzones that are low in O 2 can facilitate N 2 fixation. In contrast, in the oceans and
activity, there are free-living and symbiotic N 2 -fixing microorganisms, many of
them cyanobacteria, associated with the unicellular algae, the “plants” of the oceans
which dominate oceanic primary production. There is also some N 2 fixation in
marine sediments catalysed by free-living bacteria and possibly Archaea, but at
relatively low rates due to the presence of fixed combined N which can repress the
synthesis and activity of nitrogenase. In some lakes, rivers and estuaries, low N
availability relative to phosphorus stimulates dense growth or blooms of N 2 -fixing
cyanobacteria, most often heterocyst-forming. N 2 fixation is important in the lownutrient oligotrophic regions of the open ocean. The magnitude of N 2 fixation in the
marine environment is difficult to quantify but is an important input and will be
discussed in detail in subsequent chapters.
References
Baas-Becking, L. G. M. (1934). Geobiologie; of inleiding tot de milieukunde. Den Haag: WP Van
Stockum & Zoon NV.
Barnard, R., Leadley, P. W., & Hungate, B. A. (2005). Global change, nitrification, and denitrification: A review. Global Biogeochemical Cycles, 19(1), 1–13.
Canfield, D. E., Glazer, A. N., & Falkowski, P. G. (2010). The evolution and future of Earth’s
nitrogen cycle. Science, 330(6001), 192–196.
Dworkin, M., & Gutnick, D. (2012). Sergei Winogradsky: A founder of modern microbiology and
the first microbial ecologist. FEMS Microbiology Reviews, 36(2), 364–379.
Falkowski, P. G. (2015). Life’s engines: How microbes made habitable (224 p.). Princeton:
Princeton University Press.
Falkowski, P. G., Fenchel, T., & Delong, E. F. (2008). The microbial engines that drive Earth’s
biogeochemical cycles. Science, 320(5879), 1034–1039.
Galloway, J., Dentener, F., Capone, D., Boyer, E., Howarth, R., et al. (2004). Nitrogen cycles: Past,
present and future. Biogeochemistry, 70, 153–226.
Galloway, J. N., Townsend, A. R., Erisman, J. W., Bekunda, M., Cai, Z., et al. (2008). Transformation
of the nitrogen cycle: Recent trends, questions, and potential solutions. Science, 320(5878),
889.
Gottschalk, G. (2012). Bacterial metabolism. New York: Springer.
Howard, J. B., & Rees, D. C. (1996). Structural basis of biological nitrogen fixation. Chemical
Reviews, 96, 2965–2982.
Moore, C., Mills, M., Arrigo, K., Berman-Frank, I., Bopp, L., et al. (2013). Processes and patterns
of oceanic nutrient limitation. Nature Geoscience, 6(9), 701–710.
1 Nitrogen Fixation in the Marine Environment