Impact of lignite on pedogenetic processes and microbial functions in Mediterranean soils
Résumé
We compared a calcareous soil developed from a lignite vein (natural outcrop) and a control adjacent soil without lignite in order to assess the impact of lignite on pedogenetic processes and microbial functions in Mediterranean soils. Lignite was evidenced by the C-14 analysis, delta C-13 signature and SS C-13 CPMAS NMR spectroscopy in the various soil horizons. Physico-chemical (particle size analysis, pH, total organic carbon, carbonate content, nitrogen, sulfur, cation exchange capacity, crystalline and amorphous Fe and Al, mineralogy, bulk density) and biological (enzyme activities: beta-glucosidase, arylsulfatase, acid phosphatase, arylamidase, fluorescein dilaurate hydrolase and fluorescein diacetate hydrolase; basal respiration and Biolog (R) catabolic profile) properties were also analyzed in all horizons. We showed that the naturally-occurring lignite modified soil organic matter quality and mineralogy and improved some soil properties such as clay content, C-org, CEC and porosity. On the contrary, lignite had a higher C/N and higher recalcitrant C content compared to recent soil organic matter, which resulted in a decrease in the expression of microbial soil functions involved in the turn-over of the main bio-elements C, N, P and S due to lignite acting as a diluting factor (i.e. inert regarding microbial activities). The information derived from this study offers insight on the long term fate of lignite in soil, especially relevant if lignite is aimed at being used as amendment. (C) 2014 Elsevier B.V. All rights reserved.