Nutrients and Growth Flashcards
Nutrient
Dissolved substnces from which organisms can obtain an element which is essential for growth
Biological functions
Phosphorous required to construct key biomolecules, such as DNA and phospholipids
Nitrogen is required for DNA and a major component of proteins
Fe is required to build proteins
Phosphorous chemical forms
Dissolved inorganic phosphate or orthophosphate
Dissolved organic phosphorous
Nitrogen chemical forms
N gas, largely unreactive
Nitrate, majority of fixed N in the oceans
Nitrite
Ammonia mostly as ammonium
Dissolved organic N, urea
Silica chemical form
Soluble in water as silicate ion
Iron chemical forms
Fe III, highly unsoluble at pH8
Fe II, more soluble, rapidly oxidised small pool
Bound to organic ligands
Redfield ratio
C:N:P - 106:16:1
Stoichiometric ratios within average phytoplankton biomass.
138 O
Formula for average OM:
(CH2O)106(NH3)16(H3PO3)
Production of OM represented by equations, can relate C to oxygen by photosynthetic quotient, mols of O consumed to C produced
Vertical profiles
Depleted in surface
Enriched in sub-surface waters by degradation of OM
Major N pools in the sea
N is unavailable to most organisms except diazotrophs
Availability of N is often a constraint on production of new OM
N uptake and assimilation
Synthesis of AAs requires N in form of ammonium into C skeletons
Two sources of nutrients to euphotic:
- local regeneration.
Influx of external nutrients from deep ocean or atmosphere
- 15N can be used as a tracer to estimate the uptake of different forms of N
new N species in the sea
Nitrate, microbial oxidation produces a large pool below thermocline, replenishes waters through upwelling
Nitrite, accumulated in regions of low oxygen, max at base of euphotic, due to phyto excretion
N gas, N fixation in trichodesmium.
Regenerate N species
Ammonium formed from bacterial deamination and animal excretion
Urea bacterial degradation of purines and pyrimidines
N15 uptake experimetn
Spike and incubtate
Filiter, collect particles
Measure (IRMS)
F ratio
Uptake of new N / uptake of new N + regenerated N
F-ratio in different systems
Eutrophic f ratio >60%
Oligotrophic 3-20%
HNLC 30-50%
Nutrient Limitations
N and Fe limiting
Affets yield or crop biomass and rate of growth
Total new biomass produced may be dependant on the minimum amount of limiting nutrient available
Rate of growth may be dependent on the concentration of the limiting nutrient.
Nutrient uptake equation
Uptake of inorganic nutrients is a hyperbolic function of the nutrient concentration:
v = Vmax [S] / Kn + [S]
v= rate of uptake
Vmax= max rate of uptake
S = nutrient conc
Kn = saturation constant
Competition for nutrients
Different types of microbe will vary in their nutrient uptake kinetics
Smaller cells tend to have a lower Kn due to larger SA:V
If all other characteristics remain the same, smallest cells will be the best competitors at low nutrient concs
how to assess
Nitrogen limitaion
Method for assession:
Collect water and in situ microbes
Add potentially limiting nutrients
Measure response
Iron
Fe is largely insoluble and highly particle reactive in oxic sea water.
Sticky and sinks with particles to deep ocean
Fe inputs are low
Southern Ocean Iron Release
Fe to labelled patch of water
When performed in HNLC regions, marked blooms occur
Bloom of SOIREE could be observed from space over a month after initial release
Natural iron input
Volcanic activity input Fe
Iron controls on upper ocean ecosystems
Small cells:
low Fe need
low chlorophyll
Use ammonia
Larger cells:
Higher Fe need
Higher chlorophyll
Use nitrate
