Biological impact on mineral dissolution: Application of the lichen model to understanding mineral weathering in the rhizosphere

Abstract

Microorganisms modify rates and mechanisms of chemical and physical weathering and clay growth, thus playing fundamental roles in soil and sediment formation. Because processes in soils are inherently complex and difficult to study, we employ a model based on the lichenmineral system to identify the fundamental interactions. Fixed carbon released by the photosynthetic symbiont stimulates growth of fungi and other microorganisms. These microorganisms directly or indirectly induce mineral disaggregation, hydration, dissolution, and secondary mineral formation. Model polysaccharides were used to investigate direct mediation of mineral surface reactions by extracellular polymers. Polysaccharides can suppress or enhance rates of chemical weathering by up to three orders of magnitude, depending on the pH, mineral surface structure and composition, and organic functional groups. Mg, Mn, Fe, Al, and Si are redistributed into clays that strongly adsorb ions. Microbes contribute to dissolution of insoluble secondary phosphates, possibly via release of organic acids. These reactions significantly impact soil fertility. Below fungi-mineral interfaces, mineral surfaces are exposed to dissolved metabolic byproducts. Through this indirect process, microorganisms can accelerate mineral dissolution, leading to enhanced porosity and permeability and colonization by microbial communities.

Mobilisation of potassium and phosphorus from iron ore by ectomycorrhizal fungi

“…Slime produced by microorganisms largely consists of polysaccharides that can bind metals from solution (Banfield et al 1999). Such a process can possibly create a concentration gradient that can increase movement of ions from mineral into solutions (Delvasto et al 2009).…”

“…This is one of the mechanisms that fungi generally used to solubilise minerals (Burgstaller and Schinner 1993). Apart from the direct binding of elements from the minerals, attachment to mineral surfaces also enhance a particular feeding mechanism in fungi known as scavenging (Banfield et al 1999;Delvasto 2009). Closeness of the fungal mycelia to the mineral surface during scavenging promotes direct absorption of nutrients contained inside the mineral.…”

The effect of phytostabilization on Zn speciation in a dredged contaminated sediment using scanning electron microscopy, X-ray fluorescence, EXAFS spectroscopy, and principal components analysis

“…This phenomenon, which was observed in the six vegetated pots (SAT, SFR, STSAT, STSFR, SAPAT and SAPFR), suggests that plants increased the solution concentration of Mg, Al and Si, in addition to Zn. Silicate minerals, whose dissolution rate has been shown to be enhanced by biota (White, 1995;Barker et al, 1998;Banfield et al, 1999), are the main source of Mg, Al and Si. The role of plants on mineral dissolution was investigated for plagioclase (Berner, 1995;Bormann et al, 1998; real world studies of the mineralogy of the rhizosphere (Kodama et al, 1994;Courchesne and Gobran, 1997;Nordborg and Olsson, 1999;Egli et al, 2003).…”

Fate of Trace Metals in Anaerobic Digestion

“…under sulfidic condition and extensive metal-sulfide precipitation), microbes are able to excrete strong metalbinding organic compounds to facilitate the uptake of essential metals. These extracellular organic compounds encompass strong metal binding properties and in many cases may result in enhanced solubility of metal-bearing minerals [49]. A well-studied example is microbial Fe acquisition by excretion of Fe-chelating siderophores and further uptake by cognate receptors [50].…”