Lignin signatures show the effects of changes in heather and bracken coveron the composition of organic matter in a moorland soil profile

Bracken (Pteridium aquilinium) is aggressively displacing heather (Calluna vulgaris) on many moorlands in Britain. We investigated the use of lignin d erivatives to identify the distribution of soil organic matter (SOM) derive d from bracken in moorland soil profiles formed under heather. Phenylpropan oids extracted from recently senesced litters, roots and SOM, using alkalin e CuO oxidation, showed distinct signatures for bracken and heather, with v anillyl moieties dominating bracken litter extracts and vanillyl and syring yl dominating heather litter extracts, Ratios of vanillyl and syringyl conc entrations characterised the SOM derived from heather and bracken better th an the concentrations of the individual moieties. The analysis showed up to a. depth of 5 cm under pure bracken cover, and at the interface between he ather and bracken, the SOM was largely derived from bracken litter but belo w that depth SOM was apparently derived from heather. The use of these meth ods to identify the plant origin of SOM not only enables understanding the effects of changing vegetation cover on organic matter dynamics in moorland soils but could also facilitate management techniques in moorland/heathlan d restoration which involve the removal of comparatively nutrient-rich SOM derived from bracken.