Characteristics and pedogenesis of podzolic forest soils along a toposequence near a subalpine lake in northern Taiwan

摘要

Podzolic soils are commonly found under cypress forests in the subalpine region of northern Taiwan where the climatic conditions are cold and humid. Toposequential change from summit to lake shore along a subalpine lake (Lake Jialo) was selected to evaluate the influence of high soil moisture conditions on vegetation and pedogenic processes, and to clarify the mechanism of podzolization. Along this toposequence, the podzolization process occurs at all landscape sites except for the one at the lakeshore. Organically-complexed Fe and Al are the dominant forms in the Bs horizons at summit and footslope sites. The fulvic acids complex Fe and Al and translocate the latter downwards into the Bs horizons. The placic horizon in soils at the footslope is dominated by amorphous Fe oxides. Formation of placic horizons is mainly attributed to perched water, which is caused by heavy rainfall and seasonally high lake water level between the AE and Bs horizons. This situation causes Fe reduction and translocation to lower parts of the soil profile, resulting in formation of a placic horizon between E and Bs horizons. The soils towards the lakeshore are characterized by increasing dominance of hydromorphic process over podzolization. However, although the podzolization process occurs, the studied soils cannot be classified as Spodosols. High clay and crystalline Fe oxide contents derived from parent materials retard the mobility of organically-complexed metal cations and thus slow down the podzolization process and formation of spodic horizons in this area.