Change of ecochemical indicators as a result of introducing beech undergrowth into pine stands

The aim of the presented research was to assess the changes in selected ecochemical indices along the vertical precipitation profile - rainwater passing through the tree canopy and penetrating the topsoil. Two Scots pine stands were selected for this comparison (at one of them beech undergrowth was introduced), located at the Tuczno research site near the existed eddy covariance tower. The concentration of basic cations and anions in the collected water samples was measured and the following indices were calculated: Acid Neutralising Capacity (ANCaq), Alkalinity (ALK), Basic Cation Saturation (BS%) and Calcium to Aluminum ratio (Ca/Al). Additionally, Dry Deposition Factor (DDF) and Canopy Exchange for potassium, calcium, and magnesium cations were estimated (CE_K+, CE_Ca2+and CE_Mg2+, respectively). Observed changes in these variables values in throughfall (TF), as compared to bulk precipitation, at both pine stands during the investigated period 2013–2015 indicate that rainwater was enriched with almost all analyzed ions after passing through the canopy. Moreover, the mean annual deposition of all elements in throughfall was higher in the pine stand with beech undergrowth (SP + Bch) than at the plot with Scots pine only (SP). The average value of the DDF index was almost 3 times higher in the pine stand with beech undergrowth than at solely pine stand. Along with the depth in the soil profile, the ANCaq and ALK decreased. The main conclusion was that introduction of beech undergrowth in the pine stand most likely resulted in the accumulation of more organic matter and thus a slower decomposition rate, as suggested by an increase in acidification of the topsoil (0–15 cm). However, such an effect was not visible in the deeper layers. Higher values of ALK, ANCaq, and pH value under pine stand with beech undergrowth indicate positive effect of beech undergrowth in pine stands.