A comparison of plant and microbial biomarkers in grassland soils from the Prairie Ecozone of Canada

Abstract

Free and bound lipids and CuO oxidation products from four grassland soils that developed from similar parent materials, vegetation, relief, and time but under different climatic conditions were analyzed using solvent extraction, chemolysis and gas chromatography–mass spectrometry (GC–MS) to assess the stage of soil organic matter (SOM) decomposition. In general, the more northern soils (Black Chernozems) yielded less free and bound lipids and CuO products than those in the southern region (Brown Chernozems). The solvent extracts contained a series of long-chain aliphatic lipids, steroids, and triterpenoids. Most of the free lipids were typical constituents of higher plant waxes while biomarkers for microbes represented minor components. A series of aliphatic lipids and several phenols were detected in the soils after base hydrolysis. The predominant long-chain ω-hydroxyalkanoic and α,ω-alkanedioic acids are typical biomarkers for suberin and indicate a major input of root-biomass to the soils. Cutin-derived short-chain hydroxyacids (C 16, C 18) and phenols originating from suberin and ligno-cellulose were also detected. The CuO oxidation products comprised benzyls, lignin phenols and short-chain diacids and hydroxy acids. The lignin composition with equal proportions of vanillyl, syringyl, and cinnamyl units reflect its origin from non-woody angiosperms. The similar composition of free and bound lipids and lignin degradation products in all soils analyzed is consistent with the same type of overlying vegetation (prairie grasses). Different stages of SOM degradation in the Brown and Black Chernozems are indicated by the extract yields and degradation parameters of lignin and cutin/suberin. Lower yields of recognizable products of SOM biodegradation and parameters indicating a higher stage of degradation while exhibiting higher C contents were observed in the Black Chernozems. The results suggest that the plant-derived biomolecules in the Black Chernozems are altered into less biodegradable structures (“humification”) and are accumulated in the SOM. The observations are in accordance with the formation of the soils in this climosequence and imply that there are large reserves of recalcitrant components in the northern part of the Prairie Ecozone.