Differences in Soil Solution Chemistry and Their Vertical Variation Between Moso Bamboo Forests and Japanese Cedar Plantations in Western Japan

Bamboo invasion into adjacent forests highlights the need to clarify its ecological impacts, particularly on soil solution chemistry, which influences forest nutrient availability and downstream water quality. This study examined how bamboo invasion alters base cations and anion concentrations, their vertical distribution, and the distinct ionic compositions maintaining charge balance in soil solution by comparing Moso bamboo (BF) and adjacent Japanese cedar (CF) forests. In surface soil solution (5 cm), most ion concentrations were significantly higher in CF than in BF, likely attributable to a greater interception of atmospheric nitrogen resulting from taller tree height in CF. In vertical distribution, CF showed generally higher ion concentrations in surface soil solution than at 50 cm, whereas in BF, this phenomenon was observed only for NO3−, NH4+, and K+, consistent with bamboo’s high demand for macronutrients. Significant correlations between the concentration of NO3− and those of Ca2+ and Mg2+ were absent only in BF soil leachate. Conversely, a deficit of strong anions showed a significant correlation with the concentration of Ca2+ and Mg2+ in BF soil leachate, with HCO3− identified as a potentially major component. Our findings provide insights into the concomitant-ion relationships between base cations and NO3− across forest types and soil depths.