Mineral Cycles Flashcards
What are the inorganic forms of sulfur?
Sulfate, sulfite, thiosulfate, elemental sulfur and sulfide
Sulfate
Most abundant sulfur compound, which is anionic and soluble, and usually the form assimilated by microorganisms, immobilised when reduced, unavailable for uptake
Mineralisation
Transformation of unavailable compounds into available ones
Mineralisation of Sulfur…
First-order reaction depending on substrate concentration, thus mineralisation rates deplete over time, with sulfhydryl bond ester cleavage releasing compunds
Example of Sulfur redox reactions?
SO42-/Thiosulfate used as a terminal electron acceptor in respiration
Products of redox reactions…
Oxidised S compounds like sulfate may be used as an electro acceptor at certain redox potential
Reduction produce gaseous by-products which are toxic
Sulfate reduction in sewage treatment plants…
Cathodic depolarisation is spontaneous reaction of sulfate reduction of iron in pipes
Thiobacilli
Primary S oxidisers, usually inactive, increase with sulfur addition, used to outcompete actinomycetes when S acidifies soils
P stores…
Soils and rocks, not atmosphere cyclical
What are the forms of P?
Soluble Orthophosphate
Organic forms
Mineral forms(apatite)
When does Orthophosphate become avaialble?
With alkalinity and association with Na, but can precipitate with Ca, Fe and Mg
Most common organic P forms?
Inositol phosphate and plant-precipitated inositol hexaphosphate(phytin)
Microbial P cycling importance in crops…
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.
How might P become available?
Destabilisation by oxalic acid chelation with minerals.
Solubiltiy of mineral found in, ferric Fe less soluble than Ferrous, dissolving.
Acidity dissolves minerals
Organic P availability…
Requires mineralisation, favoured by thermophilic temperatures, neutral-to-alkaline pH and OM rich in P…
What performs organic P mineralisation?
Phytases and phosphotases which can be extracellular, inhibited by excess inorganic P
Influence of Mycorrhizae of P…
Organic acid/CO2 production solubilises P
Extending root surface area for contacting P-containing compounds
Extracellular phosphatase secretion
Conditions of P environmental management…
P mostly immobile due to rapid precipitation thus stratifies in surface horizons devoid of cultivation like no-tillage
Example of Fe minerals formed by microbes…
Goethite(Iron Hydroxide oxidation), hematite and pyrite(Fe and H2S)
What is redox state of Fe determined by?
pH and redox potential: O2 and NO3 supress Fe3 reduction, increasing redox potential.
When does gleying occur?
Microbe oxidation of Fe as an electron acceptor
How might ferric Fe be solubilised?
Acidification/Complexation with organic material, podzolisation solublises Fe with organic acids/precipitation to B horizons
Examples of chelating compounds sourcing Fe?
Hemes, transferrins, ferritin, humic acids, oxalate.
