ix
Preface
Nitrogen (N) is a fundamental component of life whose availability constrains the
productivity of the biosphere. It is a unique element in being very abundant in the
atmosphere, but not available to most life in its gaseous form N 2 . N is also interesting
because it exists in multiple oxidation states, resulting in a complex biogeochemical
cycle, and can be energy sources or electron acceptors in microbial metabolisms. N 2
fixation, the reduction of N 2 to biologically available inorganic forms, is performed
by diverse but limited bacteria and archaea species. The importance of N and
biological N 2 fixation has long been known in the terrestrial environment. Decades
of research on the diversity, genetics, biochemistry, and symbiosis involved in N 2
fixation have led to a mature scientific understanding, although it has not yet been
possible to engineer a N 2 -fixing eukaryotic plant. Biological N 2 fixation is an important feature of ecosystems, including the oceans. Although N 2 fixation was assumed
to occur in the oceans, for decades it was not thought to be important in controlling
productivity. Instead, phosphorus availability was presumed to ultimately limit productivity, and that biological N 2 fixation would just alleviate any N deficit that
occurred. Since then, there is now not only a known appreciation for how biological
N 2 fixation controls processes in the sea, but that it is a large fraction of the biological N 2 fixation on Earth.
N 2 fixation in the oceans, since so many microorganisms are uncultivated and
because the oceans are less accessible than land, has been studied from very different
perspectives than on land. There are fundamental differences in the organisms and
the ecology compared to the terrestrial environment. The aim of this book to provide
a comprehensive basic and current understanding of marine N 2 fixation ranging
from fundamental chemistry and biology to microbiology, habitats, and ecosystems
and be a resource for microbial oceanographers and for those in other scientific
disciplines, including terrestrial N 2 fixation.
Santa Cruz, CA, USA
Jonathan P. Zehr
Los Angeles, CA, USA
Douglas G. Capone
Preface
Nitrogen (N) is a fundamental component of life whose availability constrains the
productivity of the biosphere. It is a unique element in being very abundant in the
atmosphere, but not available to most life in its gaseous form N 2 . N is also interesting
because it exists in multiple oxidation states, resulting in a complex biogeochemical
cycle, and can be energy sources or electron acceptors in microbial metabolisms. N 2
fixation, the reduction of N 2 to biologically available inorganic forms, is performed
by diverse but limited bacteria and archaea species. The importance of N and
biological N 2 fixation has long been known in the terrestrial environment. Decades
of research on the diversity, genetics, biochemistry, and symbiosis involved in N 2
fixation have led to a mature scientific understanding, although it has not yet been
possible to engineer a N 2 -fixing eukaryotic plant. Biological N 2 fixation is an important feature of ecosystems, including the oceans. Although N 2 fixation was assumed
to occur in the oceans, for decades it was not thought to be important in controlling
productivity. Instead, phosphorus availability was presumed to ultimately limit productivity, and that biological N 2 fixation would just alleviate any N deficit that
occurred. Since then, there is now not only a known appreciation for how biological
N 2 fixation controls processes in the sea, but that it is a large fraction of the biological N 2 fixation on Earth.
N 2 fixation in the oceans, since so many microorganisms are uncultivated and
because the oceans are less accessible than land, has been studied from very different
perspectives than on land. There are fundamental differences in the organisms and
the ecology compared to the terrestrial environment. The aim of this book to provide
a comprehensive basic and current understanding of marine N 2 fixation ranging
from fundamental chemistry and biology to microbiology, habitats, and ecosystems
and be a resource for microbial oceanographers and for those in other scientific
disciplines, including terrestrial N 2 fixation.
Santa Cruz, CA, USA
Jonathan P. Zehr
Los Angeles, CA, USA
Douglas G. Capone