Seasonal variation of pH_H2O and pH_CaCl2 in centimeter‐layers of mor humus in a Picea abies (L.) Karst. stand

Abstract

Ten mor cores (O‐horizon) were sampled every month during September 1985 to August 1986 (except December) from a 9 m² plot. Each core usually yielded four sliced 1‐cm‐layers in addition to the S‐layer. Each layer was extracted in both distilled water and in 0.01 M CaCl₂ The spatial pH variation was found to be greater than the seasonal variation in all layers. With few exceptions, pH_H2O and pH_CaCl2 showed a similar seasonal trend in the entire mor layer. Seasonal alteration of chemical or biological conditions generally influenced pH of all cm‐layers in the same direction. The general seasonal trend of pH_H2O and pH_CaCl2 was a‐continuous increase during autumn and winter, with a maximum in April, followed by a more drastic decrease and a pH_H2O minimum in June. The minimum pH_CaCl2appeared in August. Cation uptake (May‐June) and mineralisation, leaching and alteration of organic acid properties (September‐April, July‐August) were discussed as the dominating factors behind the seasonal pH variation.

Key words:

• pH
• exchangeable acidity
• O‐horizon
• mor layer seasonal variation
• cation uptake
• precipitation
• leaching
• Picea abies