96
Table 6.1 Environmental factors controlling marine N 2 -fixers, showing major sources of
variability and effects on diazotrophs
Type
Source or control
Factors &
variability
Fluctuations
& gradients
Effects
Physical
Temperature Solar radiation
Latitude, depth,
water clarity
Coastal-open
ocean, depth,
stratification
(seasonal and
interannual),
secular
(climate
change)
Enzyme
kinetics, growth
rates
Light
Solar radiation
Intensity, quality
(color)
Annual, daily,
secular,
turbidity,
coastaloffshore,
depth
Temperature,
photosynthetic
rates
Turbulence Wind, currents,
upwelling, tides,
advection
Season,
geomorphology,
hydrography
Estuarine,
thermal
stratification,
microscale
and
mesoscale
features
Affects nutrient
availability,
oxygen
Pressure
Hydrostatic
pressure
Water depth
Increasing
with depth
Enzyme
kinetics,
adaptation to
pressure
Chemical
Salinity
Freshwater
inputs, rivers,
estuaries, water
masses,
evaporation,
precipitation
Seasonal,
latitude
Estuaries,
annual,
interannual
Growth,
adaptation
Oxygen
Equilibrium with
atmosphere,
photosynthesis,
respiration
Organic matter
inputs, primary
productivity,
stratification,
mixing
Coastal open
ocean,
sediment
interface,
particles
Aerobic vs.
anaerobic
respiration,
chemical form,
stability,
solubility, diel
cycles,
nitrogenase
inactivation
(continued)
6 Factors Controlling N 2 Fixation