Mineral Cycles

Question 1

What are the inorganic forms of sulfur?

Answer 1

Sulfate, sulfite, thiosulfate, elemental sulfur and sulfide

Question 2

Sulfate

Answer 2

Most abundant sulfur compound, which is anionic and soluble, and usually the form assimilated by microorganisms, immobilised when reduced, unavailable for uptake

Question 3

Mineralisation

Answer 3

Transformation of unavailable compounds into available ones

Question 4

Mineralisation of Sulfur…

Answer 4

First-order reaction depending on substrate concentration, thus mineralisation rates deplete over time, with sulfhydryl bond ester cleavage releasing compunds

Question 5

Example of Sulfur redox reactions?

Answer 5

SO42-/Thiosulfate used as a terminal electron acceptor in respiration

Question 6

Products of redox reactions…

Answer 6

Oxidised S compounds like sulfate may be used as an electro acceptor at certain redox potential
Reduction produce gaseous by-products which are toxic

Question 7

Sulfate reduction in sewage treatment plants…

Answer 7

Cathodic depolarisation is spontaneous reaction of sulfate reduction of iron in pipes

Question 8

Thiobacilli

Answer 8

Primary S oxidisers, usually inactive, increase with sulfur addition, used to outcompete actinomycetes when S acidifies soils

Question 9

P stores…

Answer 9

Soils and rocks, not atmosphere cyclical

Question 10

What are the forms of P?

Answer 10

Soluble Orthophosphate
Organic forms
Mineral forms(apatite)

Question 11

When does Orthophosphate become avaialble?

Answer 11

With alkalinity and association with Na, but can precipitate with Ca, Fe and Mg

Question 12

Most common organic P forms?

Answer 12

Inositol phosphate and plant-precipitated inositol hexaphosphate(phytin)

Question 13

Microbial P cycling importance in crops…

Answer 13

Require 1-30kg of P per hectare whilst amount of dissolved P from 0.1-1kg, 10% of solubilised P is microbial in the rhizosphere, performed by chelation, Fe reduction and acidification.

Question 14

How might P become available?

Answer 14

Destabilisation by oxalic acid chelation with minerals.
Solubiltiy of mineral found in, ferric Fe less soluble than Ferrous, dissolving.
Acidity dissolves minerals

Question 15

Organic P availability…

Answer 15

Requires mineralisation, favoured by thermophilic temperatures, neutral-to-alkaline pH and OM rich in P…

Question 16

What performs organic P mineralisation?

Answer 16

Phytases and phosphotases which can be extracellular, inhibited by excess inorganic P

Question 17

Influence of Mycorrhizae of P…

Answer 17

Organic acid/CO2 production solubilises P
Extending root surface area for contacting P-containing compounds
Extracellular phosphatase secretion

Question 18

Conditions of P environmental management…

Answer 18

P mostly immobile due to rapid precipitation thus stratifies in surface horizons devoid of cultivation like no-tillage

Question 19

Example of Fe minerals formed by microbes…

Answer 19

Goethite(Iron Hydroxide oxidation), hematite and pyrite(Fe and H2S)

Question 20

What is redox state of Fe determined by?

Answer 20

pH and redox potential: O2 and NO3 supress Fe3 reduction, increasing redox potential.

Question 21

When does gleying occur?

Answer 21

Microbe oxidation of Fe as an electron acceptor

Question 22

How might ferric Fe be solubilised?

Answer 22

Acidification/Complexation with organic material, podzolisation solublises Fe with organic acids/precipitation to B horizons

Question 23

Examples of chelating compounds sourcing Fe?

Answer 23

Hemes, transferrins, ferritin, humic acids, oxalate.