Elsevier

Applied Soil Ecology

Volume 122, Part 2, January 2018, Pages 162-169
Applied Soil Ecology

Review
Humusica 2, article 11: Histic humus systems and forms–Epihisto intergrades and dynamics

https://doi.org/10.1016/j.apsoil.2017.03.001Get rights and content

Abstract

The processes of formation and evolution of Histic humipedons are related to the soil/water dynamics. In a first part of the paper we present diagnostic features and horizons necessary for describing the intergrade humipedons existing between Histic and Hydro humipedons. Called Epihistic (“superficial” Histic), these humipedons are very common and help in better defining the relationships between plant and soil in semi-terrestrial environments. In a second part of the paper we set some information about biological activities and correlated environmental frames of Histic and Epihisto units. The article concludes with dynamic relationships between humipedons, describing them in fen or bog ecosystems, allowing the interpretation of complex wetlands. The present manuscript updates the description and classification of semi-terrestrial humus forms previously published by Zanella et al., 2011a, Zanella et al., 2011b.

Section snippets

Specific terms and diagnostic horizons

Intergrades between Histic and Terrestrial humus systems are necessary for understanding the processes of litter transformation and soil formation in wet ecosystems (Fig. 1).

Names of Epihistic intergrades

When concomitance of histic (H or anA) and hydromorphic horizons (gOH or/and gA), the prefix “Epihisto” (from “Epi”, superficial, and “Histic”, submerged humus forms) is set before the name of the corresponding Histic form.

Examples of names of Epihistic Anmoors:

  • Epihisto Anmoor = anA or lHS or HS/anA + gzoA or/and gOH

  • Euanmoor = anA; Epihisto Euanmoor = anA + gzoA or gOF or gOH

  • Limianmoor = lHS/anA; Epihisto Limieuanmoor = lHS/anA + gzoA or/and gOF and gOH

  • Saprianmoor = HS/anA; Epihisto Saprianmoor = HS/anA + gzoA

Dynamic specificities

Epihistic forms can be grouped according to the process of formation in three categories:

  • stationary thin Histic forms in which decomposition matches accumulation of organic matter. They develop in mesotrophic environments such as groundwater fed areas, brookvalleys and wet depressions (rather common) and generate Epihistic Anmoor and Saprimoor;

  • real initial forms generated as a consequence of a dynamic evolution from Terrestrial Hydro forms into Epihisto Histic soil conditions in different ways.

Simplified table of classification of Histic forms and Epihisto intergrades

All encountered Epihistic humus forms are reported in Fig. 7. Epihistic diagnostic horizons are reported on both sides of the table in the grey-green columns. Each main Histic system has been subdivided in two, three or four humus forms according to the thickness ratio of the composing diagnostic horizons and using the following prefixes:

  • Fibri, Mesi, Humi and Sapri along a gradient of increasing biological activity and consequent transformation of the HF (fibric) horizon in an HS (sapric)

Bioactivity of Histic humus systems and forms

In water-saturated systems, the bioactivity, and with it the decomposition of organic plant residues, depend on water quantity, oxygen availability, water quality (pH, nutrients and bases) and quality of the peat itself, mineral content included. All these factors are closely related and form the complex which describes the main peat-forming systems (Stortelder et al., 1998).

The water quantity can be described in terms of water level and oxygen availability, which vary with frequency and

Bioactivity in bogs and rain-fed floating fens

In fens, bogs and springs the fluctuation of the water table is rather small. Decomposition in oxygen-poor circumstances (a constant state of water saturation) is mainly directed by anaerobic microorganisms (Scheffer et al., 1982). As a result, the level of mineralization, humification and mixing of the organic material is very low (Fig. 9). The accumulation of almost unaltered plant remains is the main humus forming process here. The humus form in this kind of environment is mainly a

Bog and fen vegetation dynamics

Fens and bogs often show dynamic relationships (Fig. 10). In temperate climates (not mountain, not boreal, not arid, not tropical), where biological activity is moderate during most of the year, the formation of bogs succeeds that of fens (Hughes and Barber, 2003). Starting with base-rich water, fed by groundwater, a pond (whether issued from natural or man-made cavities) appears after its bottom has been made impermeable (sealing) through the sedimentation of very fine mineral particles

Springs and brook valleys

At the more base-rich and more mineral end of the Semiterrestrial spectrum, such as springs and groundwater-fed wet brook valleys, the accumulation of organic matter is not spectacular and most bioactivity is due to actinomycetes (Scheffer et al., 1982). In these circumstances, rather rich Anmoor humus forms will develop. Under the influence of lower pH and lower calcium availability, a much poorer Anmoor will form, the activity of actinomycetes being decreased (Fig. 9, Fig. 10).

In wet brook

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