Dr Adam Gillespie1, Dr Bert Vandenbygaart2, Dr Ed Gregorich2, Dr Bobbi Helgason3
1University Of Guelph, Guelph, Canada, 2Agriculture and Agri-Food Canada, Ottawa, Canada, 3University of Saskatchewan, Saskatoon, Canada
Tillage and water erosion are fundamental soil forming factors in hummocky landscapes. Soil organic matter (SOM) is redistributed horizontally and vertically, thereby exposing subsoil carbon at erosional positions and preserving C by burial in depositional positions. Here we explore the links between microbial communities and organic matter chemistry across an erosion/deposition-affected prairie catena. Original A-horizon material at this site has been buried for ca. 70 y, is >55 cm below the current surface, and contains ca. 6% organic C. Total lignin phenol contributions to total soil C were lowest in the buried A horizons compared to surface soils. Microbial alteration of lignins also was highest in buried A horizons. Amino sugar residues were greatest in the buried C-rich soil layers due to selective enrichment of glucosamine. Analysis by XANES (NEXAFS) of the bulk SOM indicated that buried soil layers contained a high proportion of functional groups such as ketones and pyridines, indicative of repeated microbial C and N turnover. High-level microbial taxonomy (Phyla) was strongly correlated with the relative abundance of SOM functional groups associated with substrates or products of metabolism. Lignin alteration, amino sugar content, and spectroscopic evidence of microbially-degraded organic matter suggests that the microbial community altered the SOM in response to available resources and environmental conditions in this spatially and temporally complex landscape. Environmental conditions deep in the soil profile exert selective pressures on the microbial communities in buried C-rich layers, resulting in an enhanced prominence of microbial by-products as stabilized C. Study of this unusual C-rich environment provides a unique insight into the microbial controls on soil C cycling which may be occurring at small spatial scales within microsites and aggregates, or over a long time scales (decades).