Nutrients and Growth

Question 1

Nutrient

Answer 1

Dissolved substnces from which organisms can obtain an element which is essential for growth

Question 2

Biological functions

Answer 2

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

Question 3

Phosphorous chemical forms

Answer 3

Dissolved inorganic phosphate or orthophosphate
Dissolved organic phosphorous

Question 4

Nitrogen chemical forms

Answer 4

N gas, largely unreactive
Nitrate, majority of fixed N in the oceans
Nitrite
Ammonia mostly as ammonium
Dissolved organic N, urea

Question 5

Silica chemical form

Answer 5

Soluble in water as silicate ion

Question 6

Iron chemical forms

Answer 6

Fe III, highly unsoluble at pH8
Fe II, more soluble, rapidly oxidised small pool
Bound to organic ligands

Question 7

Redfield ratio

Answer 7

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

Question 8

Vertical profiles

Answer 8

Depleted in surface
Enriched in sub-surface waters by degradation of OM

Question 9

Major N pools in the sea

Answer 9

N is unavailable to most organisms except diazotrophs
Availability of N is often a constraint on production of new OM

Question 10

N uptake and assimilation

Answer 10

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

Question 11

new N species in the sea

Answer 11

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.

Question 12

Regenerate N species

Answer 12

Ammonium formed from bacterial deamination and animal excretion
Urea bacterial degradation of purines and pyrimidines

Question 13

N15 uptake experimetn

Answer 13

Spike and incubtate
Filiter, collect particles
Measure (IRMS)

Question 14

F ratio

Answer 14

Uptake of new N / uptake of new N + regenerated N

Question 15

Nitrogen uptake in different systems

Answer 15

Eutrophic f ratio >60%
Oligotrophic 3-20%
HNLC 30-50%

Question 16

Nutrient Limitations

Answer 16

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.

Question 17

Nutrient uptake equation

Answer 17

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

Question 18

Competition for nutrients

Answer 18

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

Question 19

Nitrogen limitaion

Answer 19

Method for assession:
Collect water and in situ microbes
Add potentially limiting nutrients
Measure response

Question 20

Iron

Answer 20

Fe is largely insoluble and highly particle reactive in oxic sea water.
Sticky and sinks with particles to deep ocean
Fe inputs are low

Question 21

Southern Ocean Iron Release

Answer 21

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

Question 22

Natural iron input

Answer 22

Volcanic activity input Fe

Question 23

Iron controls on upper ocean ecosystems

Answer 23

Small cells:
low Fe need
low chlorophyll
Use ammonia
Larger cells:
Higher Fe need
Higher chlorophyll
Use nitrate