Monday, August 3, 2009 - 4:00 PM

OOS 3-8: Selective transfer of root-derived biomolecules to soil organic matter pools

Timothy R. Filley, Purdue University


Changes in the rate and type of plant input to litter and soil can have a cascading influence on the biogeochemical processes that control short and long term cycling of soil organic matter (SOM).  The same is true for the relative input of root and above ground litter to soil with many recent studies indicating that belowground sources have the greater influence on SOM stabilization and soil structure dynamics. Soil fauna can also have a dramatic influence on both relative source apportionment, type of decomposition, and degree of mineral soil interaction.  It is difficult, however, to determine the relative contributions of above and below ground sources.  Even at the biomarker level, there is significant overlap in molecular composition of biomarkers derived from cutin, suberin, and lignin, among root and leaf.  Additionally, the relative abundance of the molecular components that make up the macromolecules are known to change during decay of may have environment specific relative decay rates.  Such differences can make source designations equivocal. The main tool in the investigations presented herein is alkaline CuO oxidation which decomposes suberin, cutin, and lignin into GC-amenable fragments. This chemical extraction was followed by structural analysis and compound-specific stable carbon isotope analysis

Results/Conclusions We present results from forests systems of different successional stage to investigate the relative role of leaf and root litter contribution to soil fractions and the possible influence of invertebrate activity on their distribution.  In general this biomarker approach indicates that most soils investigated, soil particles isolated based upon either microaggregate association or mineral association, exhibit selective accrual of either leaf vs root tissue in different particles. For example, in a young successional sweet gum plantation where fine root productivity is increasing relative above ground leaf input our molecular indicators suggest that root-derived tissue was quantitatively more important for non-microaggregated POM while foliar tissue is selectively accrued in microaggregated POM, silts and clays.  Analysis of the fecal material from soil fauna from this site illustrate the important role of certain larvae and worms in this apportionment.  Additionally, in other systems with gradients in earthworm activity the molecular ratios of lignin and cutin and suberin markers indicate relative input of root material to POM decreases with increased activity of some earthworms.  Leaf vascular tissue such as petioles, that are rich in lignin, selectively accrue in particulate soil organic matter fractions due to selective decomposition of leaf blades by litter decomposing worms.