PHENOLIC AND CARBOHYDRATE SIGNATURES OF ORGANIC-MATTER IN SOILS DEVELOPED UNDER GRASS AND FOREST PLANTATIONS FOLLOWING CHANGES IN LAND-USE

Comparisons were made between the phenolic and carbohydrate signatures of soil profiles developed under grass, spruce and ash stands. Sample s were collected from a brown earth soil which was originally under th e same land use, but over the past 43 years has supported different mo nocultures. Distinct signatures associated with each litter type were recorded in individual profiles. A relatively undecomposed phenolic fr action from lignin and hydrolysable carbohydrate fraction from plants had accumulated in the soils under spruce and ash. This largely reflec ted the quantity and quality of the litter inputs from the spruce and ash compared with the grass. The phenolic and hydrolysable carbohydrat e fractions accounted for as much as 60% of the total organic carbon c oncentration in the deep horizons. In the grassland profile both fract ions were more decomposed than under ash and spruce suggesting that th e forest profiles had rapidly accumulated a carbon pool with a compara tively slow rate of decomposition. This was most apparent from the spr uce profile (which contained 398 mg g(-1) C carbohydrate hydrolysed us ing trifluoracetic acid (TFA) in the C horizon compared with 165 and 4 5 mg g(-1) C under ash and grass respectively). We conclude that the d ecay rate of these fractions is a function of the vegetation type.