vii
Foreword
The oceans, with a global surface area of >70% and an average depth of over
3500 m, are the largest habitat for living organisms on Earth, and microbial activity
there plays a major role in the global N cycle. In the late nineteenth and early part
of the twentieth centuries, N 2 fixation by marine microbes was little studied and was
thought to be a minor contribution to the Earth’s N cycle. In early attempts in the
late 1800s at assessing the biomass and concentration of the cyanobacterium
Trichodesmiumn, before the advent of flowmeters, and before it was known to be
able to fix N 2 , nets were lowered vertically with the mouth closed to 200 m, then
pulled up through the water column with the mouth open. Later, in the 1970s,
mechanical Clark-Bumpus opening/closing nets were towed at selected depths to
assess vertical population structure. More recently, the populations can be assessed
underway using digital optical counting devices. In the early 1960’s, Richard
Dugdale and coworkers, who introduced enriched
15
N 2 as a tracer for marine N 2
fixation, demonstrated that Trichodesmium was able to fix N 2 . There were doubters
however because Trichodesmium didn’t possess heterocysts, anoxic cells found in
some cyanobacteria that were then known to be the sites of N 2 fixation, and they
labeled the observation as “Nitrogen Fiction.” With the advent of rapid sea-going
gas chromatographic methods for indirectly measuring nitrogenase activity in the
early 1970s, it was shown that N 2 fixation in the global ocean was a significant part
of the marine N cycle. This led to updated concepts of marine N cycling, diazotrophic organisms, and N 2 fixation rates by several contributing authors to the book
Nitrogen in the Marine Environment in 1983 (Carpenter and Capone 1983) and in a
subsequent edition in 2008 (Capone et al. 2008).
This volume, written by Jon Zehr and Doug Capone, colleagues in the quest to
put together new discoveries on the marine N cycle and how it functions biologically,
is a beautiful and rich compendium of the state of knowledge of marine N 2 fixation
today. The chapters start with an introduction and review of the fundamentals of the
process of N 2 fixation and the history of marine N 2 fixation research. Subsequent
chapters describe habitats and organisms responsible for N 2 fixation and the rates of
N 2 fixation in different ecosystems. The factors controlling N 2 fixation rates, such as
water temperature, nutrient availability, and other environmental controls, are
Foreword
The oceans, with a global surface area of >70% and an average depth of over
3500 m, are the largest habitat for living organisms on Earth, and microbial activity
there plays a major role in the global N cycle. In the late nineteenth and early part
of the twentieth centuries, N 2 fixation by marine microbes was little studied and was
thought to be a minor contribution to the Earth’s N cycle. In early attempts in the
late 1800s at assessing the biomass and concentration of the cyanobacterium
Trichodesmiumn, before the advent of flowmeters, and before it was known to be
able to fix N 2 , nets were lowered vertically with the mouth closed to 200 m, then
pulled up through the water column with the mouth open. Later, in the 1970s,
mechanical Clark-Bumpus opening/closing nets were towed at selected depths to
assess vertical population structure. More recently, the populations can be assessed
underway using digital optical counting devices. In the early 1960’s, Richard
Dugdale and coworkers, who introduced enriched
15
N 2 as a tracer for marine N 2
fixation, demonstrated that Trichodesmium was able to fix N 2 . There were doubters
however because Trichodesmium didn’t possess heterocysts, anoxic cells found in
some cyanobacteria that were then known to be the sites of N 2 fixation, and they
labeled the observation as “Nitrogen Fiction.” With the advent of rapid sea-going
gas chromatographic methods for indirectly measuring nitrogenase activity in the
early 1970s, it was shown that N 2 fixation in the global ocean was a significant part
of the marine N cycle. This led to updated concepts of marine N cycling, diazotrophic organisms, and N 2 fixation rates by several contributing authors to the book
Nitrogen in the Marine Environment in 1983 (Carpenter and Capone 1983) and in a
subsequent edition in 2008 (Capone et al. 2008).
This volume, written by Jon Zehr and Doug Capone, colleagues in the quest to
put together new discoveries on the marine N cycle and how it functions biologically,
is a beautiful and rich compendium of the state of knowledge of marine N 2 fixation
today. The chapters start with an introduction and review of the fundamentals of the
process of N 2 fixation and the history of marine N 2 fixation research. Subsequent
chapters describe habitats and organisms responsible for N 2 fixation and the rates of
N 2 fixation in different ecosystems. The factors controlling N 2 fixation rates, such as
water temperature, nutrient availability, and other environmental controls, are