Abstract
The budget of water-soluble base cations in a forest soil system is presumably balanced between inputs via canopy throughfall, Ao-layer and soil release (mainly by organic decomposition and ion exchange with soil colloid), and outputs via biological uptake and leaching. An in situ method combining ion exchange resin (IER) bag and core ion exchange resin (core-IER) was adopted in this study to investigate water-soluble base cation dynamics in an 18-yr-old Japanese cedar (Cryptomeria japonica D. Don) stand over a 7-month period. Chemical characteristics of the canopy throughfall and the soil solution beside the IER bags were also measured. Inputs of K, Ca, Mg to the soil system via canopy throughfall, Ao-layer & soil release differed greatly from each other. Canopy throughfall provided 54% of the total input of K to the soil, and Ao-layer and soil release provided 12% and 34%, respectively. Ao-layer and soil release supplied more Ca and Mg (85% and 78%) to the soil than canopy throughfall (15% and 22%). Among the outputs, biological uptake accounted for 66% of K, 42% of Ca and 45% of Mg. The higher biological uptake of K in comparison with Ca and Mg indicated that potassium was rapidly recycled in this forest ecosystem. Evaluation of the applicability of the in situ combined IER method suggested that this method may be useful for comparative analysis of water-soluble cation dynamics in a forest soil.
