Organic geochemical studies of soils from the Rothamsted classical experiments - V. The fate of lipids in different long-term experiments

Lipid extracts from four long-term experiments (Broadbalk Wilderness, Geesc roft Wilderness, Hoosfield Spring Barley and Park Grass) were analysed usin g a combination of gas chromatography, gas chromatography-mass spectrometry and gas chromatography-combustion-isotope ratio mass spectrometry. The lip id content of the primary organic inputs for each soil were also analysed i n order to assess the early diagenetic fate of the various compound classes present. Soil pH was observed to either directly or indirectly, have a sig nificant effect on lipids with a relative increase in abundance of n-alkane s at higher pH (7.31) and a large relative increase in n-alkanoic and omega -hydroxy acids at low pH (3.74). Triacylglycerols exhibited severe losses i rrespective of pH. In an arable soil, n-alkanoic acids showed a temporal de crease in concentration whilst levels of n-alkanols remained static, the di fference was ascribed to a more rapid turnover and possible leachate migrat ion of the n-alkanoic acids. The phytosterol, sitosterol, was observed to r apidly diminish in soils possibly as a result of assimilation by soil dwell ing invertebrates. Analysis of 5 beta-stigmastanol (a faecal biomarker) sho wed that it remained at levels indicative of manuring even after 113 years. Furthermore, analysis of 5 beta-stanyl esters revealed a manuring signal e ven more persistent than that exhibited by the free stanols. Knowledge of t he biogeochemical cycling of lipids in the soil environment will help facil itate understanding of the processes which underpin carbon cycling in soils . (C) 2000 Elsevier Science Ltd. All rights reserved.