Effect of parent material on soil acidity and carbon content in soils under silver fir (Abies alba Mill.) stands in Poland

• We investigated the influence of parent materials on total soil acidity.
• Total soil acidity was fractionated into hydrogen (HTA) and aluminium (AlTA).
• The content of fine fractions increased soil acidity.
• AlTA was greater in TS, while the content of HTA was similar in TS and QSW soils.
• AlTA and HTA appeared to have a similar impact on soil carbon content.

The objective of this research was to investigate the influence of parent materials on soil acidity, particularly pH, fractions of aluminium (AlTA) and hydrogen (HTA), and their effect on soil organic matter accumulation in acid forest soils under silver fir stands. We established 86 investigation plots with soils developed from Triassic sandstones, TS (33 plots), and Quaternary sand derived from weathering of sandstones, QSW (53 plots). Soil samples of the A horizons were analysed for pH measured in water extract (pHw), the content of carbon (Ct), base cations (BCEX) and total acidity (TA). Additionally, TA was fractionated into HTA and AlTA. We also analysed chemical composition of water extracts. Soils developed from TS were significantly richer in clay and Ct than QSW soil. The mean pHw of soils developed from TS and QSW was similar. TA was significantly greater in TS soils; however, this difference was only related to the content of AlTA. Conversely, the content of HTA was similar in TS and QSW soils. The content of Ct and TA soil showed a moderate significant positive correlation with clay content (r = 0.50 and 0.60, respectively). The TA correlation was largely attributed to AlTA (r = 0.60), while HTA was not correlated with clay content. The positive correlation between clay content and TA suggests that clay fraction increases soil acidity. Higher TA of TS soils was particularly related to the higher AlTA content, while the content of HTA was not related to either parent material or clay content. Small differences in soil pHw between the investigated parent materials may result from the similar relationship between AlTA and Ct. AlTA and HTA appeared to have a positive similar impact on soil Ct.