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© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
J. P. Zehr, D. G. Capone, Marine Nitrogen Fixation,
https://doi.org/10.1007/978-3-030-67746-6_5
Chapter 5
Measurements of Organism Abundances
and Activities
5.1 Introduction
The significance of N 2 fixation in the environment can be assessed by a variety of
means providing differing perspectives, each with their own strengths and weaknesses. These include methods to determine the composition and identity of N 2 -
fixers in various marine communities and their activity at scales from individual
cells to ecosystems and ocean basins. Understanding the types of organisms that are
the major N 2 -fixers has implications for the role of diazotrophs in food webs as well
as the fate of fixed N in the ecosystem. Examining marine N 2 -fixers also informs us
about the unique physiologies and adaptations that have developed in these organisms. In contrast, to understand the roles of N 2 fixation in the productivity of the
oceans, including for predictions of the future, integrated basin-scale measures are
the most relevant. Such approaches, based on a number of biogeochemical proxies,
largely ignore the organisms.
As for many scientific fields, advances in microbial oceanography are often constrained by the technologies and approaches available. Rapid advances in oceanographic sampling and analytical methods and instrumentation in general were
occurring through the 1960s and greatly facilitated the sampling and analysis of
marine phytoplankton and microbial communities (DeLong and Karl 2005). For N 2
fixation, four particular advances propelled the field forward: the introduction of
isotopic tracer methodologies to directly measure rates of N 2 fixation, the acetylene
reduction assay as a facile method to determine nitrogenase activity in the field, the
development of biogeochemical proxies for examining N 2 fixation at the large scale
and the introduction of molecular biology, genomics and metagenomics approaches
to detect, identify and quantify the diverse populations of microbial diazotrophs in
marine systems.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
J. P. Zehr, D. G. Capone, Marine Nitrogen Fixation,
https://doi.org/10.1007/978-3-030-67746-6_5
Chapter 5
Measurements of Organism Abundances
and Activities
5.1 Introduction
The significance of N 2 fixation in the environment can be assessed by a variety of
means providing differing perspectives, each with their own strengths and weaknesses. These include methods to determine the composition and identity of N 2 -
fixers in various marine communities and their activity at scales from individual
cells to ecosystems and ocean basins. Understanding the types of organisms that are
the major N 2 -fixers has implications for the role of diazotrophs in food webs as well
as the fate of fixed N in the ecosystem. Examining marine N 2 -fixers also informs us
about the unique physiologies and adaptations that have developed in these organisms. In contrast, to understand the roles of N 2 fixation in the productivity of the
oceans, including for predictions of the future, integrated basin-scale measures are
the most relevant. Such approaches, based on a number of biogeochemical proxies,
largely ignore the organisms.
As for many scientific fields, advances in microbial oceanography are often constrained by the technologies and approaches available. Rapid advances in oceanographic sampling and analytical methods and instrumentation in general were
occurring through the 1960s and greatly facilitated the sampling and analysis of
marine phytoplankton and microbial communities (DeLong and Karl 2005). For N 2
fixation, four particular advances propelled the field forward: the introduction of
isotopic tracer methodologies to directly measure rates of N 2 fixation, the acetylene
reduction assay as a facile method to determine nitrogenase activity in the field, the
development of biogeochemical proxies for examining N 2 fixation at the large scale
and the introduction of molecular biology, genomics and metagenomics approaches
to detect, identify and quantify the diverse populations of microbial diazotrophs in
marine systems.