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 ¹³C 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.