Humusica 1, article 2: Essential bases—Functional considerations

doi:10.1016/j.apsoil.2017.07.010

Applied Soil Ecology

Volume 122, Part 1, January 2018, Pages 22-41

https://doi.org/10.1016/j.apsoil.2017.07.010 Get rights and content

Highlights

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What is a humus system? Functional consideration.
•
Darwin, Dokuchaev, or Jenny?
•
Which are the main factors arresting litter biodegradation?
•
Can temperature influence humus decomposition?

Abstract

Humusica 1 and 2 Applied Soil Ecology Special issues are field guides for humipedon classification. Contrary to other similar manuals dedicated to soil, the objects that one can describe with these guides are living, dynamic, functional, and relatively independent soil units. This is the reason to why the authors dedicated the whole article number 2 to functional considerations even before readers could go in the field and face the matter to be classified. Experienced lectors can overstep many of the sections reported in this article. If the titles of sections “1 A functional classification", "2 What is a humus system?"and "3 Energetic considerations in terrestrial systems” stimulate the reader’s curiosity, then we suggest to pass through them. Otherwise, only section “4 Climatic, plant litter, or nutritional constraints?” is crucial. Readers will understand how the soil works in terms of litter and Carbon accumulation, which one(s) among climatic, vegetational, or geological factors that intervene and strongly affect the formation processes of terrestrial (oxygenated) soils. The article concludes with a debate about a tergiversated question: can temperature influence humus decomposition? Preceding statements were used for explaining how the biological soil net can store in the soil a maximum of energy in the form of SOM, by raising a plateau partially independent of climatic conditions.

Section snippets

A functional classification

Classifying makes sense only if the established categories of objects correspond to a few references allowing us to better understand the observable real world (see also in Humusica 1, Article 1: Essential bases – Vocabulary and Article 7: Terrestrial humus systems and forms – Field practice and sampling problems). We have named these references Humus forms (= theoretical groups of humus profiles displaying the same series of diagnostic horizons) and Humus systems (= theoretical groups of humus

What is a humus system?

The humipedon – the upper part of a soil made of organic and/or organic-mineral horizons – is directly under the influence of the aboveground parts of an ecosystem. The humipedon constitutes an interaction system born to manage a functional transition between organic and mineral worlds. This humus system has the possibility to degrade structured organic matter and use it as a source of energy. Further, it may act as a sink and a source of energy. Due to the process of photosynthesis, plant

Energetic considerations in terrestrial systems

The large-scale approach (point 2 of Section 1) has to consider the most important parameter while discussing ecosystem functioning: energy. No energy, no life. Sun sends high amounts of energy to Earth. Ignoring clouds, the average insolation for the Earth is approximately 250 W per square meter (= 6 kWhm⁻² day⁻¹). In fact, over the course of a year the average solar radiation arriving at the top of the Earth's atmosphere is roughly 1366 W per square meter of ground. Sun rays are attenuated as they

Climatic, plant litter, or nutritional constraints?

It is not astonishing that this fundamental question was raised by eminent Naturalists. They proposed, however, discording solutions.

Humus systems as an eco-device

Why are we interested in humus forms? Why are we trying to classify them? Why are we investigating processes of biodegradation? All these questions go back to the intuitive feeling that humus is useful for human beings. It might be useful as a source of ‘free’ nutrients needed for crop growth or timber production. It might provide a structure protecting soils from erosion. It might be an interesting sink for carbon sequestration in respect to the problem of climate warming. Also, the humus

Carbon sequestration and decomposition 1

The title covers part of a complex concept and it may be a good start telling a short story. While telling the story we will focus on three main points, which are connected, namely;

(i) Sequestration of carbon in humus. (ii) Steady state for humus. (iii) Humus decomposition vs rate- regulating factors.

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A bizarre layer cake: Why soil animals recolonizing polluted areas shape atypical humus forms
2023, Science of the Total Environment
During soil recolonization by macrofauna in areas previously defaunated by industrial pollution, non-typical humus forms are produced. Given that the evidence of zoogenic activity cessation with increased forest litter depth in these humus forms, we tested the hypothesis that the lower organic layers are more toxic than the upper ones. The studies were conducted in the southern taiga, near the Middle Ural Copper Smelter (Revda city, Russia), in spruce-fir and birch forests. We investigated the series of degraded humus forms at different recovery stages, including those without signs of regradation, as well as at the initial and advanced recovery stages. In the organic layers, each of which were 1–2 cm thick and 6–8 cm in total, we measured the following parameters: pH(water), total acidity, the content of exchangeable Ca²⁺ and Mg²⁺, acid-soluble and exchangeable metals (Cu, Pb, Fe, Cd, and Zn), organic carbon, and total nitrogen. Simultaneously, we diagnosed the degree of zoogenicity of the organic layers following the European morpho-functional classification of humus forms. Concentrations of the metals increased with forest litter depth, reaching a maximum at the boundary between the organic and organic-mineral horizons (the difference exceeded an order of magnitude). In the same direction, the acidity increased, but the saturation of the exchange complex with Ca²⁺ and Mg²⁺ decreased. Within a particular forest litter profile, metal concentrations and acidity were lower in the layer with the highest zoogenicity compared to the layer with the lowest zoogenicity. Based on the metals, pH(water), and exchange complex, the accuracy of the predictions of the degree of layer zoogenicity within the OF horizon in the discriminant analysis reached 100 %. These findings suggest that the vertical gradient of toxic burden persisting in the forest litter after pollution cessation can explain the recovery pattern of humus forms in the contaminated areas.
Technogenic parent materials drive Technosols humus system formation on an industrial brownfield
2023, Catena
The study of humus systems provides a lot of information on soil ecological functioning, such as fauna functional community, soil nutrient status, organic matter decomposition, and microbial food web. Technosols have highly heterogeneous physicochemical properties and so far, their humus systems are poorly described and the mechanisms behind their formation are still largely to be studied. In order to fill this knowledge gap, this study was conducted to get better understanding of the factors involved in the development of different Technosols humus system after brownfield rehabilitation. Our sampling strategy followed a pollution diagnostic report and allowed to cope with the spatial heterogeneity of the studied area. We studied 24 soil profiles and identified 3 different humus systems on two different rehabilitation substrates: 7 Mull, 3 Amphi and 14 Techno-moder. Our results showed that the development of zoOH horizon resulted from the nature of underlying horizons but not from the main litter type. On Techno-moder, the accumulation of organic matter in the form of fecal pellets as a zoOH horizon resulted in an increase of 130% of nitrogen on soil surface. Contrary to what was expected, we did not find a threshold of heavy metals leading to the formation of zoOH horizon, with highest lead concentration found in the A horizon of Mull systems. Transmission electron microscopy (TEM) analysis showed that neoformed organic matter is biochemically stabilized as condensed polyphenols and melanized hyphae. EDX analysis revealed that such ultrastructures are associated with Ca and Zn that may explain their stability on the Technosols surface. Development of zoOH horizon on Technosols built from coking plant by-products allowed to improve soil surface chemical and biological properties. The evolution of the humus systems as a result of vegetation succession and microbial community composition should be further studied to specify the mechanisms involved in Technosols humus system dynamics.
Humipedon dynamics in lowland Amazonian forests: are there Amphi humus forms even in tropical rain forests?
2022, Geoderma
Understanding humipedon dynamics is crucial to capture forest ecological processes. However, studies disentangling humipedon dynamics in tropical forests are scarce. The humipedon structure classification is important because it shows how forest ecosystems interact and react with (a)biotic factors. Here, we used the humus morpho-functional approach to investigate how soil texture and reduced impact-logging affect forest humipedon structure and dynamics in the eastern Amazon. We used a morpho-functional classification of humus forms as the foundation to visualize, classify, and code 133 soil profiles in two contrasting soil textures and different post-logging practices, to identify litter leaching, fragmentation, and humification processes coupled with soil aggregation and root dynamics. The classification of humus forms resulted in the identification of three humus systems: Mull, Moder and Amphi. Sandy and clayey textures differ statistically (χ² = 51.83; p < 0.001), with sandy texture predominating in Moder system, while clayey texture exhibits Amphi or Mull systems. Sandy textures presented a weak soil aggregation, but strong association with root (rhiOF) and humification (OH) horizons, leading to a clear transition between organic and mineral pools. In contrast, clayey textures show a strong carbon storage and soil aggregation. The humipedon horizons differ significantly (p = 0.009; stress = 0.1142 and R² = 0.987) and their dynamics clearly evolve towards an opposite direction. The classification framework introduced here supports environmental management by promoting speed and viability in diagnosing forest ecosystem soils towards forest protection or use in the landscape, and specific climate mitigation goals both in local and regional planning.
Non-typical degraded and regraded humus forms in metal-contaminated areas, or there and back again
2021, Geoderma
Citation Excerpt :
Humus in the pedological sense (humus form, humus profile) has been investigated for nearly a century and a half. One of the most prominent achievements of recent years in this domain is the European morpho-functional classification of humus systems and forms (hereafter referred to as the Classification) (Zanella et al., 2011; Zanella et al., 2018a; Zanella et al., 2018e). The undoubted advantages of the Classification, which determine its increasing popularity, are clear diagnostic criteria, theoretical validity, internal consistency, and unification of national taxonomies and terminologies.
Chemically contaminated soils are not included in the European morpho-functional classification of humus systems and forms. However, they differ from the uncontaminated analogs in biological, chemical, and physical features. We investigated the topsoils contaminated by long-term sulfur dioxide and metal emissions from a copper smelter (southern taiga; conifer and deciduous forests; the Middle Urals, Russia). The smelter has been in operation for more than 80 years, but ten years ago, emissions almost ceased which initiated the recovery of adjacent ecosystems. We performed 1,155 humus profile descriptions on 231 sampling plots in highly contaminated, moderately contaminated, and background sites. In the contaminated sites, we found 21 non-typical humus forms that do not fit the European classification. Earthworms’ extinction caused by soil toxicity resulted in a Mull-to-Mor transformation of humus profiles. Recent recolonization of poorly decomposed litter by earthworms and other soil macrodetritivores after emission cessation triggered a Mor-to-Mull shift. Because different topsoil layers react to environmental changes with unequal rates, signs of several stages of humus evolution can be imprinted in one profile. More rapid degradation of organic horizons than organic-mineral ones results in non-typical Mor forms when the thick non-zoogenic OF combines with zoogenic A horizon. Zoogenic O horizons’ heterogeneity due to non-zoogenic inclusions, or inversion of the litter layers sequence, or lagging of A horizon recovery behind the O horizons, represents the discrepancies between non-typical regraded and typical humus forms. Mor-to-Mull recovery can occur with and without passing the Moder forms. In the first path, all intermediate stages at least fitted to one of the known humus systems. In the second path, intermediate humus forms are represented by non-zoogenic OF conjoining highly zoogenic OF and lacking OH horizon (we named such forms Mormull). In both paths, the recovery starts from the upper litter layer and spreads downward, i.e., the signs of the zoogenic activity change in the opposite direction than within the natural Mor profile. We consider the non-typical humus forms as non-equilibrium topsoil states that are ephemeral on the forest succession scale. We described non-typical humus forms in detail, proposed their evolutionary diagram, nomenclature, and preliminary typology, and extended the Humus Index with non-typical forms.
European beech leads to more bioactive humus forms but stronger mineral soil acidification as Norway spruce and Scots pine – Results of a repeated site assessment after 63 and 82 years of forest conversion in Central Germany
2021, Forest Ecology and Management
Citation Excerpt :
This classification is based on morphological and zoogenic properties of characteristic diagnostic horizons (Ol, Of, Oh resp. Oi, Oe, Oa) and are indicative for overall turnover processes (Zanella et al., 2018a). Differences in forest floor masses and properties are documented to vary with tree species, across sites and with stand age (Binkley, 1995).
To reduce the effects of extended coniferous monoculture plantations on forest floor and topsoil processes, like amplified acidification or nutrient immobilization in organic layers, small interspersed groups of European beech were planted at the beginning of the 20th century amid large coniferous stands (CS) in Central Germany. Today, these so-called “Green Eyes” (GE) are 82-year old. In our study we focused on two different timelines to investigate the effects of forest conversion on vegetation composition, forest floor and mineral soil properties, encompassing a long-term (>80 year) comparison from tree planting in the 1930s to 2018 and a shorter timeframe nearly spanning 20 years (1999–2018). Since long-term forest conversion experiments (>60 years) across sites sharing a common forest land-use history are scarce, our study allows to contribute to a better evaluation of the long-term effects on changes in soil properties. We linked standard methods assessing soil pH, organic C and total N concentrations as well as stocks as indicators of soil quality changes in forest floor and mineral soil (down to 40 cm depth) to patterns in ground vegetation dynamics (most GE were characterized only by a few herbaceous species). Our results exhibited an effect of forest conversion on the activation in forest floor turnover resulting in increased turnover rates in the GE (GE contain only half of the forest floor OM of CS), hence forming more bioactive humus forms (mull, moder) and a noticeable higher forest floor pH (+0.6 units) compared to CS. The OC translocation from the forest floor into the topsoil is higher under GE (+0.7% OC content), probably building up a stable SOC pool hence contributing to C sequestration. The positive effects of European beech on forest floor quality are related to a stronger acidification of the subsoil during the past 20 years (-0.5 pH units). The base pump effect (uptake of Ca²⁺, Mg²⁺, K⁺ and assimilation into tree biomass in exchange release of H⁺) in GE led to more acidic conditions (- 0.2 pH units) in the deeper mineral soil compared to CS. This bio-acidification may serve as one reason for subsoil acidification, as observed in our study, pointing out that mineral soil acidification is still an important issue in central European forests. Future restoration of soil base cation pools will still depend on the rate of bio-acidification, on the amount of acidifying air pollutant (and base cation) depositions and on forest management practices (e.g. intensity of biomass removal, soil regeneration-oriented liming).
Techno-moder: A proposal for a new morpho-functional humus form developing on Technosols revealed by micromorphology
2020, Geoderma
Human impact on soil systems is now widely acknowledged. “Technosols” appeared in soil classification only a decade ago and the notion of “techno humus system” has emerged even more recently. Yet the variety of humus forms that could develop on Technosol remains largely unknown. To contribute to filling this knowledge gap, we studied the humus form developing on two Technosols resulting from the activity of a former coking plant and compared it with one developed on a Cambisol as a reference for the area. We used field description and micromorphology on thin sections coupled with a point-and-count method to precisely describe the surface of the humipedons of the area studied. A total of 13,841 counts and identifications were performed on 11 thin sections and spread into 17 fabric units. Micromorphology on thin soil sections revealed that epi-saprophagous organisms transformed most of the neo-formed organic matter on the Technosols studied, leading to an accumulation of feces on the surface of the humipedon. Our results suggested that the humus form developing on the Technosols was similar to a moder and exhibited the same ectorganic horizons (OL, OF, zOH), whilst overlaying a technogenic one composed mostly of coal fragments. We would like to propose the term “techno-moder” for this new humus form, developing in the absence of an A horizon. On the other hand, micromorphology allowed us to classify the humus form developed on the Cambisol as a eumull containing anthropic coal by-products. Specification of the humus form developing on such soils could represent a promising way to specify pedological processes such as organic matter decomposition, soil aggregation and also to enrich the humus form classification on Technosols.

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Applied field research articleHumusica 1, article 2: Essential bases—Functional considerations☆

Highlights

Abstract

Section snippets

A functional classification

What is a humus system?

Energetic considerations in terrestrial systems

Climatic, plant litter, or nutritional constraints?

Humus systems as an eco-device

Carbon sequestration and decomposition 1

Geoderma

For. Ecol. Manage.

For. Ecol. Manage.

Soil Biol. Biochem.

Chemosphere

Eur. J. Soil Biol.

Soil Biol. Biochem.

For. Ecol. Manag.

Geoderma

Soil Biol. Biochem.

Revisitation Concepts Paleopedol. Quaternary Int.

Anal. Chim. Acta

Carbon sequestration rates in organic layers of boreal and temperate forest soils – Sweden as a case study

Global Ecol. Biogeogr.

Application of fractals to soils studies

Adv. Agron.

Succession, Resource Processing, and Diversity in Detrital Food Webs

Are humus forms, mesofauna and microflora in subalpine forest soils sensitive to thermal conditions?

Biol. Fert. Soils

A tale of four stories: soil ecology, theory, evolution and the publication system

PLoS One

Resource quality in a soil food web. Is nitrogen or labile carbon more important for soil nematodes?

Biol. Fertil. Soils

Géologie de la matière organique

Ecology−From Individuals to Ecosystems

Nutrient dynamics in some leaf and needle litter types of different chemical composition in a Scots pine forest

Scand. J. For. Res.

Validating a new model for N sequestration in forest soil organic matter

Water Air Soil Pollut. Focus

Litter mass-loss rates and decomposition patterns in some needle and leaf litter types. Long-term decomposition in a Scots pine forest VII

Can. J. Bot.

Decomposition of Needle and Root Litter in Lodgepole Pine and Scots Pine Monocultural Systems. Research Notes No. 53

Decomposition of needle litter in lodgepole pine and scots pine monocultures—a comparison

Scand. J. For. Res.

Plant Litter. Decomposition. Humus Formation. Carbon Sequestration

Plant Litter, Decomposition. Humus Formation. Carbon Sequestration

Litterfall in some European coniferous forests as dependent on climate – a synthesis

Can. J. For. Res.

Litter quality in a north European transect versus carbon storage potential

Plant Soil

Changes in organic-chemical components during decomposition. Long-term decomposition in a Scots pine forest I

Can. J. Bot.

Data on needle litter decomposition and soil climate as well as site characteristics for some coniferous forest sites

Section 2. Data on Needle Litter Decomposition. Report No. 42

Litter mass loss in pine forests of Europe and Eastern United States as compared to actual evapotranspiration on a European scale

Biogeochemistry

The chemical composition of newly shed needle litter of different pine species and Scots pine in a climatic transect. Long-term decomposition in a Scots pine forest X

Can. J. Bot.

Some foliar litter types have a maximum limit for decomposition—a synthesis of data from forest systems

Can. J. Bot.

Site Descriptions for Forest Sites—a Compilation

Estimated N concentration in humus as based on initial N concentration in foliar litter—a synthesis

Can J Bot

Litter decomposition in a transect of Norway spruce forests: substrate quality and climate control of mass-loss rates

Can. J. For. Res.

Humus build-up in boreal forests-effects of litter fall and its N concentration

Can. J. For. Res.

Litter decomposition rates as dependent on litter Mn concentration

Biogeochemistry

Sequestration of carbon in the humus layer of Swedish forests Å direct measurements

Can. J. For. Res.

Factors influencing limit values for pine needle litter decomposition: a synthesis for boreal and temperate pine forest systems

Biogeochem.

Manganese dynamics in decomposing foliar litter ?a synthesis

Can. J. For. Res.

A Maximum Limit for Foliar Litter Decomposition—a Synthesis of Data from Forest Systems. Reports from Departments of Forest Ecology and Forest Soils

Initial rates and limit values for decomposition of Scots pine and Norway spruce needle litter – a synthesis for N-fertilized forest stands

Can. J. For. Res.

Initial rates and limit values for decomposition of Scots pine and Norway spruce needle litter—a synthesis for N-fertilized forest stands

Can. J. For. Res.

Applied field research article
Humusica 1, article 2: Essential bases—Functional considerations☆