Carbon stabilization and microbial growth in acidic mine soils after addition of different amendments for soil reclamation

Resumen

The extreme soil conditions in metalliferous mine soils have a negative influence on soil biological activity andtherefore on soil carbon estabilization. Therefore, amendments are used to increase organic carbon content andactivate microbial communities. In order to elucidate some of the factors controlling soil organic carbon stabilization in reclaimed acidic mine soils and its interrelationship with microbial growth and community structure, weperformed an incubation experiment with four amendments: pig slurry (PS), pig manure (PM) and biochar (BC),applied with and without marble waste (MW; CaCO3). Results showed that PM and BC (alone or together withMW) contributed to an important increment in recalcitrant organic C, C/N ratio and aggregate stability. Bacterialand fungal growths were highly dependent on pH and labile organic C. PS supported the highest microbial growth;applied alone it stimulated fungal growth, and applied with MW it stimulated bacterial growth. BC promoted thelowest microbial growth, especially for fungi, with no significant increase in fungal biomass. MW+BC increasedbacterial growth up to values similar to PM and MW+PM, suggesting that part of the biochar was degraded, at leastin short-term mainly by bacteria rather than fungi. PM, MW+PS and MW+PM supported the highest microbialbiomass and a similar community structure, related with the presence of high organic C and high pH, with immobilization of metals and increased soil quality. BC contributed to improved soil structure, increased recalcitrantorganic C, and decreased metal mobility, with low stimulation of microbial growth.