Pedogenic processes of placic and spodic horizons in subtropical subalpine forest soils with contrasting textures

Abstract

Summary Placic (Bsm) and spodic (Bhs) horizons are common in subalpine or alpine forest soils in Taiwan. Bsm horizons are found more usually in finer textured soils than those with Bhs horizons. To understand the different formation processes in Bsm and Bhs horizons in a humid subtropical ecosystem, we identified micro‐morphological features by using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and electron probe micro‐analysis (EPMA), and determined the physiochemical properties by chemical extractions and clay mineralogy. The study included four pedons with well‐developed Bsm horizons from our previous study and four with well‐developed Bhs horizons at other sites. Both sites were in subtropical mountain forests with similar climate, topography and general geology but over regoliths with distinctly different textures. Micro‐morphology revealed a vughy (small cavities lined with in‐washed materials) microstructure in Bsm horizons but a granular structure with bridge microstructures between coarse grains in Bhs horizons. Chemical analysis revealed more free pedogenic iron (Fed) and aluminium (Ald) in Bsm than in Bhs horizons, but more organically complexed Al (Alp) in Bhs horizons. Energy dispersive spectrometry revealed predominant Fe, oxygen (O) and carbon (C) in the matrix of the Bsm horizons, whereas Al, silicon (Si) and C were the major elements of interstitial materials in Bhs horizons. Polarizing microscopy and EPMA spectra confirmed the illuvial nature of organic Al complexes in Bhs horizons. The transformation of clay minerals showed more intense podzolization in Bhs horizons than in Bsm horizons. The different formation mechanisms in Bsm and Bhs horizons result from contrasting texture; redox processes are predominant in Bsm horizons because of the clayey texture whereas podzolization is predominant in sandy Bhs horizons.

Characterization of soil organic matter in perhumid natural cypress forest: comparison of humification in different particle-size fractions

“…Podzolic soils are commonly found under Chamaecyparis forests in the cold and humid subalpine region in Taiwan (Chiu et al 1999 ; Jien et al 2010a , b 2013 ). The extremely high acidity and soil moisture in such undisturbed Chamaecyparis forest results in low diversity of soil bacterial communities (Lin et al 2010 2011 ) as well as low decomposition of organic matter and humification degree of humic acids (Chung et al 2012 ).…”

Examination of long-term soil development and phosphorus dynamics in a hypermaritime chronosequence, Calvert Island, British Columbia, Canada

“…For example, placic horizons were formed in the Cropp River Basin within 1,500 years with > 10,000mm of MAP (Tonkin and Basher, 2001), whereas placic horizons did not form in Cooloola, southern Norway, or southern Sweden (Thompson, 1981;Mokma et al, 2004;Sauer et al, 2008;Turner et al, 2012a). Interestingly, placic horizons are prevalent in northeastern Taiwan, particularly in finer soils derived from shale and sandstones in areas with > 3200 mm MAP (Wu and Chen, 2005;Jien et al, 2013). Due to the change in texture between the albic and cambic horizon, Wu and Chen (2005) hypothesized that during storms, water would become perched between these horizons and thus the deposition of Fe occurred with the change in redox potential.…”