Humus form

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The term humus form is not the same as the term humus. Forest humus form describes the various arrangement of organic and mineral horizons at the top of soil profiles. [1] It can be composed entirely of organic horizons, meaning an absence of the mineral horizon. [2] Experts worldwide have developed different types of classifications over time, and humus forms are mainly categorized into mull, mor, and moder orders in the ecosystems of British Columbia. [2] Mull humus form is distinguishable from the other two forms in formation, nutrient cycling, productivity, etc.

Contents

Formation

The formation of mull humus form results from various factors, including regional climate, parent rock, vegetation, and soil organism. [3] Mull order presents in deciduous forests, and the development is often associated with a mild climate in terms of warm temperature and moderate precipitation, also rich soil parent materials. [4] Soil organisms, including invertebrates and microbes, are the agents for the intimate mixing of soil organic matter into the mineral soil rather than organic matter accumulation on the surface, leading to the humus form of mull order. [2]

Earthworms are the dominant fauna group in the mull order. [4] They break down the decomposed material into small pieces and mix those residues into the soil through their activity, having significant roles in decomposition. Thus, conducting abundant clay-mineral complexes in the macro-structured A horizon. [5] The functions of the earthworms have a decisive influence on the control of soil organic matter levels. [5] Other agents may also contribute to incorporating soil organic matter into the mineral soil, such as white rot fungi and bacterias belonging to the microbial group. [3] They act as essential decomposers, facilitating the breakdown process of organic residues. Potential horizons included in the mull order are L, F, H, and Ah horizons, with no consideration of B or C horizons in humus form. [2]

Characteristics

Mull humus has a more rapid and complete decomposition. Due to the presence of soil organisms and high biological activity, the disappearance of plant litter is fast, and there are no distinct layers because thick organic horizons do not accumulate. [1] Conversely, the Ah horizon is well developed, resulting from the assemblage of organic matter with mineral particles. Broadleaf tree species, the significant components in the deciduous ecosystem aligned with mull humus, appear to be effective in building soil organic matter levels. [6] Also, plants under the mull humus produce litters that are easier decomposable with a low C:N ratio, allowing nutrient release, preventing immobilization, and encouraging high bioturbation. [6] Moreover, a relatively complete decomposition relates to more completely oxidized organic acids, promoting a higher value of pH and base saturation in the soil. [7]

Biodiversity and fertility

Mull humus form is the cause and result of plant-soil relationships. Litter quality, soil nutrient availability, and organism activity are related. [3] Mull humus has high biomass and species richness of soil fauna, ranging from megafauna to microfauna. [8] Those soil organisms have high nutrient requirements because they have high energy costs for capturing spaces and nutrients under high competition, explaining the fast use of nutrients. [9] Also, the variety of organisms reflects nutrient availability, which is necessary for the build-up of mull humus. Consequently, the high nutrient availability and fast use of nutrients allow rapid cycling of nutrients. [4]

A rapid nutrient cycling can further contribute to soil fertility and enrich aboveground and belowground biodiversity, indicating a high level of biodiversity and productivity. [4] Optimal plant growth depends on the degree of litter decomposition because litter provides most nutrients required by plants. [10] Associating with soil organisms, a positive feedback loop will be formed: the higher the litter quality, the faster organic matter decomposition, the faster nutrient cycling, and the faster vegetation growth. [3] More plants cohabit in mull humus, and the plant biodiversity is highly related to nutrient availability and the impacts of the soil acidity. Too much nutrient availability may negatively impact plant growth, but the high competition between soil organisms can deal with the concern. [11] The effects of mull humus on the vegetation growth are apparent.

Related Research Articles

<span class="mw-page-title-main">Ecosystem</span> Community of living organisms together with the nonliving components of their environment

An ecosystem consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the system through photosynthesis and is incorporated into plant tissue. By feeding on plants and on one another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and microbes.

<span class="mw-page-title-main">Humus</span> Organic matter in soils resulting from decay of plant and animal materials

In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Latin word for "earth" or "ground".

<span class="mw-page-title-main">Soil</span> Mixture of organic matter, minerals, gases, liquids, and organisms that together support life

Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil.

Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order (anisotropy) within soils. These alterations lead to the development of layers, termed soil horizon, distinguished by differences in color, structure, texture, and chemistry. These features occur in patterns of soil type distribution, forming in response to differences in soil forming factors.

<span class="mw-page-title-main">Detritivore</span> Animal that feeds on decomposing plant and animal parts as well as faeces

Detritivores are heterotrophs that obtain nutrients by consuming detritus. There are many kinds of invertebrates, vertebrates and plants that carry out coprophagy. By doing so, all these detritivores contribute to decomposition and the nutrient cycles. They should be distinguished from other decomposers, such as many species of bacteria, fungi and protists, which are unable to ingest discrete lumps of matter, but instead live by absorbing and metabolizing on a molecular scale. The terms detritivore and decomposer are often used interchangeably, but they describe different organisms. Detritivores are usually arthropods and help in the process of remineralization. Detritivores perform the first stage of remineralization, by fragmenting the dead plant matter, allowing decomposers to perform the second stage of remineralization.

Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have come from the feces and remains of organisms such as plants and animals. Organic molecules can also be made by chemical reactions that do not involve life. Basic structures are created from cellulose, tannin, cutin, and lignin, along with other various proteins, lipids, and carbohydrates. Organic matter is very important in the movement of nutrients in the environment and plays a role in water retention on the surface of the planet.

<span class="mw-page-title-main">Soil biology</span>

Soil biology is the study of microbial and faunal activity and ecology in soil. Soil life, soil biota, soil fauna, or edaphon is a collective term that encompasses all organisms that spend a significant portion of their life cycle within a soil profile, or at the soil-litter interface. These organisms include earthworms, nematodes, protozoa, fungi, bacteria, different arthropods, as well as some reptiles, and species of burrowing mammals like gophers, moles and prairie dogs. Soil biology plays a vital role in determining many soil characteristics. The decomposition of organic matter by soil organisms has an immense influence on soil fertility, plant growth, soil structure, and carbon storage. As a relatively new science, much remains unknown about soil biology and its effect on soil ecosystems.

Soil chemistry is the study of the chemical characteristics of soil. Soil chemistry is affected by mineral composition, organic matter and environmental factors. In the early 1850s a consulting chemist to the Royal Agricultural Society in England, named J. Thomas Way, performed many experiments on how soils exchange ions, and is considered the father of soil chemistry. Other scientists who contributed to this branch of ecology include Edmund Ruffin, and Linus Pauling.

Soil ecology is the study of the interactions among soil organisms, and between biotic and abiotic aspects of the soil environment. It is particularly concerned with the cycling of nutrients, formation and stabilization of the pore structure, the spread and vitality of pathogens, and the biodiversity of this rich biological community.

<span class="mw-page-title-main">Microbial loop</span>

The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. In soil systems, the microbial loop refers to soil carbon. The term microbial loop was coined by Farooq Azam, Tom Fenchel et al. in 1983 to include the role played by bacteria in the carbon and nutrient cycles of the marine environment.

<span class="mw-page-title-main">Soil respiration</span> Chemical process produced by soil and the organisms within it

Soil respiration refers to the production of carbon dioxide when soil organisms respire. This includes respiration of plant roots, the rhizosphere, microbes and fauna.

Soil organic matter (SOM) is the organic matter component of soil, consisting of plant and animal detritus at various stages of decomposition, cells and tissues of soil microbes, and substances that soil microbes synthesize. SOM provides numerous benefits to the physical and chemical properties of soil and its capacity to provide regulatory ecosystem services. SOM is especially critical for soil functions and quality.

<span class="mw-page-title-main">Soil carbon</span> Solid carbon stored in global soils

Soil carbon is the solid carbon stored in global soils. This includes both soil organic matter and inorganic carbon as carbonate minerals. Soil carbon is a carbon sink in regard to the global carbon cycle, playing a role in biogeochemistry, climate change mitigation, and constructing global climate models.

<span class="mw-page-title-main">Forest floor</span> Layer of the forest ecosystem above the soil composed of primarily non-living organic material

The forest floor, also called detritus, duff and the O horizon, is one of the most distinctive features of a forest ecosystem. It mainly consists of shed vegetative parts, such as leaves, branches, bark, and stems, existing in various stages of decomposition above the soil surface. Although principally composed of non-living organic material, the forest floor also teems with a wide variety of fauna and flora. It is one of the richest components of the ecosystem from the standpoint of biodiversity because of the large number of decomposers and predators present, mostly belonging to invertebrates, fungi, algae, bacteria, and archaea. Certain (adapted) plants may be more apparent in tropical forests, where rates of metabolism and species diversity are much higher than in colder climates.

<span class="mw-page-title-main">Plant litter</span> Dead plant material that has fallen to the ground

Plant litter is dead plant material that have fallen to the ground. This detritus or dead organic material and its constituent nutrients are added to the top layer of soil, commonly known as the litter layer or O horizon. Litter is an important factor in ecosystem dynamics, as it is indicative of ecological productivity and may be useful in predicting regional nutrient cycling and soil fertility.

<span class="mw-page-title-main">Invasive earthworms of North America</span>

Invasive species of earthworms from the suborder Lumbricina have been expanding their range in North America. Their introduction can have marked effects on the nutrient cycles in temperate forests. These earthworms increase the cycling and leaching of nutrients by breaking up decaying organic matter and spreading it into the soil. Since plants native to these northern forests are evolutionarily adapted to the presence of thick layers of decaying organic matter, the introduction of worms can lead to loss of biodiversity as young plants face less nutrient-rich conditions. Some species of trees and other plants may be incapable of surviving such changes in available nutrients. This change in the plant diversity in turn affects other organisms and often leads to increased invasions of other exotic species as well as overall forest decline. They do not require a mate to reproduce, allowing them to spread faster.

<span class="mw-page-title-main">Nutrient cycle</span> Set of processes exchanging nutrients between parts of a system

A nutrient cycle is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cyclic. Mineral cycles include the carbon cycle, sulfur cycle, nitrogen cycle, water cycle, phosphorus cycle, oxygen cycle, among others that continually recycle along with other mineral nutrients into productive ecological nutrition.

<span class="mw-page-title-main">Mycorrhizal fungi and soil carbon storage</span>

Soil carbon storage is an important function of terrestrial ecosystems. Soil contains more carbon than plants and the atmosphere combined. Understanding what maintains the soil carbon pool is important to understand the current distribution of carbon on Earth, and how it will respond to environmental change. While much research has been done on how plants, free-living microbial decomposers, and soil minerals affect this pool of carbon, it is recently coming to light that mycorrhizal fungi—symbiotic fungi that associate with roots of almost all living plants—may play an important role in maintaining this pool as well. Measurements of plant carbon allocation to mycorrhizal fungi have been estimated to be 5 to 20% of total plant carbon uptake, and in some ecosystems the biomass of mycorrhizal fungi can be comparable to the biomass of fine roots. Recent research has shown that mycorrhizal fungi hold 50 to 70 percent of the total carbon stored in leaf litter and soil on forested islands in Sweden. Turnover of mycorrhizal biomass into the soil carbon pool is thought to be rapid and has been shown in some ecosystems to be the dominant pathway by which living carbon enters the soil carbon pool.

Seventeen elements or nutrients are essential for plant growth and reproduction. They are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), potassium (K), sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe), boron (B), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), nickel (Ni) and chlorine (Cl). Nutrients required for plants to complete their life cycle are considered essential nutrients. Nutrients that enhance the growth of plants but are not necessary to complete the plant's life cycle are considered non-essential. With the exception of carbon, hydrogen and oxygen, which are supplied by carbon dioxide and water, and nitrogen, provided through nitrogen fixation, the nutrients derive originally from the mineral component of the soil. The Law of the Minimum expresses that when the available form of a nutrient is not in enough proportion in the soil solution, then other nutrients cannot be taken up at an optimum rate by a plant. A particular nutrient ratio of the soil solution is thus mandatory for optimizing plant growth, a value which might differ from nutrient ratios calculated from plant composition.

Moder is a forest floor type formed under mixed-wood and pure deciduous forests. Moder is a kind of humus whose properties are the transition between mor humus and mull humus types. Moders are similar to mors as they are made up of partially to fully humified organic components accumulated on the mineral soil. Compared to mulls, moders are zoologically active. In addition, moders present as in the middle of mors and mulls with a higher decomposition capacity than mull but lower than mor. Moders are characterized by a slow rate of litter decomposition by litter-dwelling organisms and fungi, leading to the accumulation of organic residues. Moder humus forms share the features of the mull and mor humus forms.

References

  1. 1 2 Brethes, A; Brun, J.J; Jabiol, B; Ponge, J; Toutain, F (1995). "Classification of forest humus forms: A french proposal". Annales des Sciences Forestières. 52 (6): 535–546. doi: 10.1051/forest:19950602 . S2CID   35885390.
  2. 1 2 3 4 Klinka, K; Green, R.N.; Trowbridge, R.L.; Lowe, L.E (1981). Taxonomic Classification of Humus Forms in Ecosystems of British Columbia: First Approximation (PDF). Province of British Columbia, Ministry of Forests.
  3. 1 2 3 4 Ponge, J (2013). "Plant–soil feedbacks mediated by humus forms: A review". Soil Biology & Biochemistry. 57: 1048–1060. doi:10.1016/j.soilbio.2012.07.019. S2CID   84606515.
  4. 1 2 3 4 Ponge, J (2003). "Humus forms in terrestrial ecosystems: A framework to biodiversity". Biology & Biochemistry. 35 (7): 935–945. doi:10.1016/S0038-0717(03)00149-4. S2CID   44160220.
  5. 1 2 Wolters, V (2000). "Invertebrate control of soil organic matter stability". Biology and Fertility of Soils. 31 (1): 1–19. doi:10.1007/s003740050618. S2CID   12522132.
  6. 1 2 Prescott, C.E.; Frouz, J; Grayston, S.J; Quideau, S.A.; Straker, J (2019). "Rehabilitating forest soils after disturbance". Developments in Soil Science. 36: 309–343. doi:10.1016/B978-0-444-63998-1.00013-6. ISBN   9780444639981. S2CID   214319901.
  7. ↑ Briggs, R.D. (2004). "Soil development and properties: The forest floor". Encyclopedia of Forest Sciences: 1223–1227. doi:10.1016/B0-12-145160-7/00241-6. ISBN   9780121451608.
  8. ↑ Petersen, H; Luxton, M (1982). "A comparative analysis of soil fauna populations and their role in decomposition processes". Oikos. 39 (2): 288–388. doi:10.2307/3544689. JSTOR   3544689.
  9. ↑ Vitousek, P (1982). "Nutrient cycling and nutrient use efficiency". The American Naturalist. 119 (4): 553–572. doi:10.1086/283931. S2CID   85128084.
  10. ↑ Vinton, M.A.; Goergen, E.M. (2006). "Plant-soil feedbacks contribute to the persistence of bromus inermis in tallgrass prairie". Ecosystems (New York). 9 (6): 967–976. doi:10.1007/s10021-005-0107-5. S2CID   36245519.
  11. ↑ Tilman, D (1999). "The ecological consequences of changes in biodiversity: A search for general principles". Ecology (Durham). 80 (5): 1455–1474. doi:10.2307/176540. JSTOR   176540.
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