Rapid molecular assessment of the bioturbation extent in sandy soil horizons under pine using ester-bound lipids by on-line thermally assisted hydrolysis and methylation-gas chromatography / mass spectrometry

Each plant species has a unique chemical composition, and also within a given plant the various tissues differ from one another in their chemistry. These different compositions can be traced back after decay of the plant parts when they are transformed into soil organic matter (SOM). As a result, the composition of SOM reflects not only the plant origin, but also of the various tissues, which, consequently, mirrors an estimate of the contribution of above-ground vs. below-ground litter. From the latter distribution the extent of bioturbation (mixing of above-ground litter with the mineral soil) can be assessed. Application of Thermally assisted Hydrolysis and Methylation (THM) using tetramethylammonium hydroxide (TMAH) and subsequent analysis by GC/MS released all typical cutin- and suberin-derived aliphatic monomers (mono-, di- and trihydroxyalkanoic acids, ¿,¿-alkanedioic acids) as their methyl esters and/or ethers in a rapid manner. Using the distribution of ¿-hydroxyalkanoic acids that are present in pine needle cutin (C12 and C14) and not in root suberin and those that are present in roots but not in needles (C20 and C22) the extent of bioturbation (mixing of above-ground plant litter with the mineral soil) can be assessed. Similarly, the (9,16-dihydroxyhexadecanoic acid + 9,10,18-trihydroxyoctadecanoic acid)/(C20+C22 ¿,¿-alkanedioic acids) ratio reflects the degree of bioturbation. Three mineral soil profiles under Corsican pine with an A horizon that exhibited extensive bioturbation phenomena, and underlying C horizons with hardly or no bioturbation were investigated in order to examine the applicability of such an approach. It appeared that the A horizons had all four mentioned ¿-hydroxyalkanoic acids, while the C horizons contained virtually only the C20 and C22 members. The results not only suggest that bioturbation occurs in the A horizons, but also that possible illuviation or other transport mechanisms of ¿-hydroxyalkanoic acids seem hardly or not to occur, which is a prerequisite to apply this biomarker approach in assessing bioturbation degrees

THE FATE OF TANNINS IN CORSICAN PINE LITTER

Tannins are ubiquitous in higher plants and therefore also in litter and soils where they affect many biogeochemical processes. Despite this well recognized role, the fate of tannins in litter and mineral soils is hardly known as often only trace amounts, if any, of tannins are measured. In this study we conducted an incubation experiment using Corsican pine litter to which known amounts of tannic acid (TA) or condensed tannins (CTs) from Corsican pine were added. Using Folin-Ciocalteu as a measure for total phenolics and HCl-butanol as an assay specific for CTs, acetone/water extractable phenolics and tannins decreased with time towards very low levels. Application of Thermally assisted Hydrolysis and Methylation to litter before and after acetone/water extraction revealed that revealed that TA concentration decreased. By contrast, CTs remained to a great extent in the litter and could not be extracted suggesting that they were tightly bound