Mineral Cycles

Sulfate, sulfite, thiosulfate, elemental sulfur and sulfide

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

Transformation of unavailable compounds into available ones

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

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

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

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

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

Soils and rocks, not atmosphere cyclical

Soluble Orthophosphate Organic forms Mineral forms(apatite)

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

Inositol phosphate and plant-precipitated inositol hexaphosphate(phytin)

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.

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

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

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

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

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

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

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

Microbe oxidation of Fe as an electron acceptor

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

Hemes, transferrins, ferritin, humic acids, oxalate.