82
5.10 Experimental and Observational Formats and Scales
In discussing examination of populations of diazotrophs and their activities, we’ve
considered approaches that range from the molecular (e.g. nifH gene analysis) to the
basin (e.g. using satellite remote sensing) scale. Similarly, short term experimental
assays of activity (e.g. using C 2 H 2 reduction or enriched
15
N 2 uptake) are most often
carried out in relatively small sealed bottles whereas geochemical observations such
a N*, P* or natural abundance are made in nature and provide more integrative
insights over larger time and space scales.
Two approaches have been undertaken in order to attempt to bridge this divide.
Mesocosm studies scale up experiments from small bottles to larger formats to minimize the effects of containment and a large surface to volume ratio (often referred
to as “bottle” effects) (Zobell and Anderson 1943). For marine N 2 fixation, small
format mesocosms (20 L) have been used successfully to study N 2 -fixer population
dynamics and have simultaneously probed for evidence of limiting factors (Zehr
et al. 2007).
More recently, researchers have scaled up mesocosm approaches substantially.
The VAHINE project undertaken in the lagoon of Noumea, New Caledonia deployed
large 50 m
3
enclosures to study the dynamics of diazotrophic populations, trophic
transfer of recently fixed N and factors limiting diazotrophs (Bonnet et al. 2016 and
references therein). A more recent mesocosm study examined the sensitivity of N 2
fixation in waters adjacent to the Cape Verde islands to ocean acidification (Singh
et al. in press).
Fig. 5.7 A surface slick of Trichodesmium observed from a Surface Processes Instrument Platform
(SPIP) drone in the SW Pacific. Inset is a sample of 300 ml of surface water under low magnification. Each colony is about 1 mm in length. (Pictures courtesy of Alex Ingle and Ajit Subramaniam,
respectively)
5 Measurements of Organism Abundances and Activities
5.10 Experimental and Observational Formats and Scales
In discussing examination of populations of diazotrophs and their activities, we’ve
considered approaches that range from the molecular (e.g. nifH gene analysis) to the
basin (e.g. using satellite remote sensing) scale. Similarly, short term experimental
assays of activity (e.g. using C 2 H 2 reduction or enriched
15
N 2 uptake) are most often
carried out in relatively small sealed bottles whereas geochemical observations such
a N*, P* or natural abundance are made in nature and provide more integrative
insights over larger time and space scales.
Two approaches have been undertaken in order to attempt to bridge this divide.
Mesocosm studies scale up experiments from small bottles to larger formats to minimize the effects of containment and a large surface to volume ratio (often referred
to as “bottle” effects) (Zobell and Anderson 1943). For marine N 2 fixation, small
format mesocosms (20 L) have been used successfully to study N 2 -fixer population
dynamics and have simultaneously probed for evidence of limiting factors (Zehr
et al. 2007).
More recently, researchers have scaled up mesocosm approaches substantially.
The VAHINE project undertaken in the lagoon of Noumea, New Caledonia deployed
large 50 m
3
enclosures to study the dynamics of diazotrophic populations, trophic
transfer of recently fixed N and factors limiting diazotrophs (Bonnet et al. 2016 and
references therein). A more recent mesocosm study examined the sensitivity of N 2
fixation in waters adjacent to the Cape Verde islands to ocean acidification (Singh
et al. in press).
Fig. 5.7 A surface slick of Trichodesmium observed from a Surface Processes Instrument Platform
(SPIP) drone in the SW Pacific. Inset is a sample of 300 ml of surface water under low magnification. Each colony is about 1 mm in length. (Pictures courtesy of Alex Ingle and Ajit Subramaniam,
respectively)
5 Measurements of Organism Abundances and Activities