Effect of vegetation on chemical composition of H horizons in incipient podzols as characterized by 13C NMR and pyrolysis-GC/MS

In a primary vegetation sequence on wind blown sands in the Netherlands, podzolization becomes evident under pine forest with various undergrowth and is more expressed under the subsequent beech forest. Recognizable podzol-B horizons appear together with H (humified O) horizons. In order to investigate whether the vegetation influences H horizon composition and the water-soluble fraction of this horizon, H horizons of three subsequent succession stages (Pinus/Empetrum-Fagus/Vaccinium-Fagus without undergrowth) were sampled, fractionated, and analysed with C-13 CPMAS-NMR, pyrolysis-GC/MS, and by pollen analysis. Water soluble and NaOH soluble fractions of the three H horizons were very similar, suggesting that the humified material in the H horizon was formed exclusively from pine litter and that beech Litter, yearly added to the soil surface in large amounts, did not influence the composition of the H horizon. The fact that the input of beech litter into the H horizon under beech was small was supported by very low amounts of Fagus pollen in all H layers. Humin fractions of the three H horizons were remarkably different, which was mainly due to varying amounts of beech root litter. The similarity of the water soluble organic matter fractions suggested that a direct relation between vegetation and organic matter mobilized by humification in the H horizon only exists under pine forest. Hence, increased podzolization under beech was probably not due to changing organic matter input, but to the factor time. (C) 1999 Elsevier Science B.V. All rights reserved.