Carbon stocks and phenolic distributions in peaty gley soils afforested with Sitka spruce ( Picea sitchensis)

Abstract

The carbon storage and phenolic distributions from two peaty gley soil profiles in northeast England have been compared. The phenols were released using on line, thermally assisted hydrolysis and methylation (THM) in the presence of tetramethylammonium hydroxide (TMAH). Two profiles were cored from peaty gley soils afforested with Sitka spruce ( Picea sitchensis); one was taken from the soil beneath a first rotation forest in Coalburn and the other was under a second rotation stand about forty miles away at Harwood Forest. The soil carbon stock under the first-rotation forest at Coalburn was 153.0 ± 34 t C ha −1, lower than the soil from the second rotation stand in Harwood Forest (431.9 ± 155 t C ha −1). THM in the presence of TMAH for the different Soxhlet extracted soils revealed a change in vegetation input and progressive lignin oxidation down each profile, as recorded in the phenol-based proxies for lignin oxidation and source. Comparison between the two profiles revealed that the phenolic accumulation in the Oe2 horizon under the Harwood second-rotation stand was not likely a result of fresh root input or leaching, as the Coalburn profile showed no evidence of phenolic accumulation in the deeper mineral horizons. Instead, soil horizon inversion, undertaken during the planting of the second-rotation forest at Harwood was more than likely responsible for both the enrichment of phenols in the Oe2 horizon and for the presence of phenols, as opposed to their absence from Coalburn, in the deeper mineral horizons.