Dados do Trabalho

Título

THE PRESENCE OF IRON (OXYHYDR)OXIDES MODULATES ORGANIC MATTER MINERALIZATION IN TEMPERATE RAIN FOREST SOILS

Resumo

The stability of soil organic matter (SOM) and mineralization in a highly humid environment is not well established because redox drives the elemental cycle, like iron transformation under anoxic conditions. In this study, sterilized SOM was incubated in an anaerobic microcosm with biogenic iron oxides (ferrihydrite, goethite, hematite, and magnetite) for 30 days to examine the properties and potential processes of oxides on the mineralization of SOM in temperate rain forest soil. This study used the facultative anaerobe Geobacter metallireducens to produce stable biogenic iron minerals under controlled chemical conditions. X-ray diffraction and oxidation state analyses determined the mineralogical compositions of the iron oxides. The release of CO2, Fe(II), and microbial biomass (MB) was measured. Magnetite enrichments produced two times more CO2 than ferrihydrite enrichments from sterilized soils with iron-reducing bacteria (2546.5 mg C-CO2 kg-1 soil). Hematite and goethite emit 854.5 mg C-CO2 kg-1 soil. Bacteria-inoculated soil exhibited a substantially lower Eh value (300 mV) than abiotic controls (Eh > 100 mV). Ferrihydrite is nearly entirely converted to lepidocrocite and goethite within three weeks in soils with the highest Fe(II) release and delayed transformation with higher goethite to lepidocrocite ratios in soils with lower Fe(II) release, according to X-ray diffraction. Oxides, especially ferrihydrite, significantly reduced SOM concentration while increasing MB content. Hematite and ferrihydrite decreased soil pH while increasing soil redox potential (Eh). The stimulation of labile organic carbon microbial assimilation, the modulation of soil chemical basic properties (pH and Eh), and the increase of MB were all potential oxide pathways in the enhancement of SOM mineralization.  

Palavras-chave

Fe(III)-reducing bacteria, CO2 released, Biogenic iron oxides

Instituição financiadora

ANID-FONDECYT regular N◦ 1220716