The microbial community uses organic C as a energy and biomass source from the residues of the structural reduction of organic macromolecules, this process is the depolymerization. The product of microbial metabolic process or mineralization is CO2.

This CO2 can react with other elements in soil solution, forming carbonates and/or bicarbonates in soil. These last are inorganic C forms and can't be mineralized, only can be solubilized. The solubilization of -CO3 may be for pH modifications associated to microbial activity but the final result for inorganic C solubilization is CO2 and only the autotrophic bacteria (such as Cyanobaterias) can use the C as CO2 for photosynthetic pathways.

not sure if I understand the question, as inorganic C is already a mineral. If you mean whether microbes can use inorganic C, photosynthetic organisms would including bacteria, archea and algae living in the soil. Again, I am uncertain of what you are asking.  

Your question is not clear. Certainly microbes use organic carbon sources for their energy. 

Maybe you want to know what the inorganic  carbon source is to be consumed by micobes. For  CaCO3, it can be dissolved by the organic acid which is able  to be produced in living process of microbes.

The microbial community uses organic C as a energy and biomass source from the residues of the structural reduction of organic macromolecules, this process is the depolymerization. The product of microbial metabolic process or mineralization is CO2.

This CO2 can react with other elements in soil solution, forming carbonates and/or bicarbonates in soil. These last are inorganic C forms and can't be mineralized, only can be solubilized. The solubilization of -CO3 may be for pH modifications associated to microbial activity but the final result for inorganic C solubilization is CO2 and only the autotrophic bacteria (such as Cyanobaterias) can use the C as CO2 for photosynthetic pathways.

@Bruno M. Chávez-Vergara

Thank you for your help. That is to say if we provide the soil microbes with CaCO3 such carbonate, only autotrophic bacteria can use the C? For the majority of microbes, the main C source are organic carbon?

Hi Xin,

I not know if any autotrophic bacterial group using the dissolution of carbonates as primary source of CO2. This process can occur but I think that the principal effect of addition of carbonate is not C fertilization, inclusive could promote a limitation in P availability that can affect microbial growth.

In general, saprotrophs microbes use the organic carbon as energy and biomass source and through of this is explained the decomposition of soil organic matter

Its an interesting topic. Here I also want to include my query. I did some work on different land uses in Mollisol where I got positive significant correlation between soil Inorganic Carbon (analysed by TOC analyzer, Shimadzu) and microbial biomass carbon, microbial quotient  (MBC/TOC) and potentially mineralizable nitrogen. How am I suppose to interpret these results?? Kindly help. Thank you.

Hi Sudeshna,

In your soils, the carbonates are derived from parental material or are secondary carbonates?

Hello Bruno,

As per my knowledge the carbonates are secondary carbonates.