Soil ecology

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Soil ecology is the study of the interactions among soil organisms, and between biotic and abiotic aspects of the soil environment. [1] 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.

Contents

Overview

Soil is made up of a multitude of physical, chemical, and biological entities, with many interactions occurring among them. Soil is a variable mixture of broken and weathered minerals and decaying organic matter. Together with the proper amounts of air and water, it supplies, in part, sustenance for plants as well as mechanical support.

The diversity and abundance of soil life exceeds that of any other ecosystem. Plant establishment, competitiveness, and growth is governed largely by the ecology below-ground, so understanding this system is an essential component of plant sciences and terrestrial ecology.

Features of the ecosystem

Soil fauna

Soil fauna is crucial to soil formation, litter decomposition, nutrient cycling, biotic regulation, and for promoting plant growth. Yet soil organisms remain underrepresented in studies on soil processes and in existing modeling exercises. This is a consequence of assuming that much below ground diversity is ecologically redundant and that soil food webs exhibit a higher degree of omnivory. However, evidence is accumulating on the strong influence of abiotic filters, such as temperature, moisture and soil pH, as well as soil habitat characteristics in controlling their spatial and temporal patterns. [2]

Soils are complex systems and their complexity resides in their heterogeneous nature: a mixture of air, water, minerals, organic compounds, and living organisms. The spatial variation, both horizontal and vertical, of all these constituents is related to soil forming agents varying from micro to macro scales. [3] Consequently, the horizontal patchy distribution of soil properties (soil temperature, moisture, pH, litter/nutrient availability, etc.) also drives the patchiness of the soil organisms across the landscape, [4] and has been one of the main arguments for explaining the great diversity observed in soil communities. [5] Because soils also show vertical stratification of their elemental constituents along the soil profile as result of microclimate, soil texture, and resource quantity and quality differing between soil horizons, soil communities also change in abundance and structure with soil depth. [6] [2]

The majority of these organisms are aerobic, so the amount of porous space, pore-size distribution, surface area, and oxygen levels are crucial to their life cycles and activities. The smallest creatures (microbes) use the micropores filled with air to grow, whereas other bigger animals require bigger spaces, macropores, or the water film surrounding the soil particles to move in search for food. Therefore, soil textural properties together with the depth of the water table are also important factors regulating their diversity, population sizes, and their vertical stratification. Ultimately, the structure of the soil communities strongly depends not only on the natural soil forming factors but also on human activities (agriculture, forestry, urbanization) and determines the shape of landscapes in terms of healthy or contaminated, pristine or degraded soils. [2]

Macrofauna

Soil macrofauna, climatic gradients and soil heterogeneity Historical factors, such as climate and soil parent materials, shape landscapes above and below ground, but the regional/local abiotic conditions constraint biological activities. These operate at different spatial and temporal scales and can switch on and off different organisms at different microsites resulting in a hot moment in a particular hotspot. As a result, trophic cascades can occur up and down the food web. Soil invertebrates are shown. Ellipses indicate hot (red) or cold spots (blue), with the curved arrows giving some examples of the factors that could switch on/off a hot moment and the straight black arrows (continuous black line = on, dashed = off) showing the implications for soil processes along the soil profile. In the boxes, the main ecosystem characteristics are listed. Soil fauna, climatic gradients and soil heterogeneity.jpg
Soil macrofauna, climatic gradients and soil heterogeneity 
Historical factors, such as climate and soil parent materials, shape landscapes above and below ground, but the regional/local abiotic conditions constraint biological activities. These operate at different spatial and temporal scales and can switch on and off different organisms at different microsites resulting in a hot moment in a particular hotspot. As a result, trophic cascades can occur up and down the food web.
Soil invertebrates are shown. Ellipses indicate hot (red) or cold spots (blue), with the curved arrows giving some examples of the factors that could switch on/off a hot moment and the straight black arrows (continuous black line = on, dashed = off) showing the implications for soil processes along the soil profile. In the boxes, the main ecosystem characteristics are listed.

Since all these drivers of biodiversity changes also operate above ground, it is expected that there must be some concordance of mechanisms regulating the spatial patterns and structure of both above and below ground communities. In support of this, a small-scale field study revealed that the relationships between environmental heterogeneity and species richness might be a general property of ecological communities. [5] In contrast, the molecular examination of 17,516 environmental 18S rRNA gene sequences representing 20 phyla of soil animals covering a range of biomes and latitudes around the world indicated otherwise, and the main conclusion from this study was that below-ground animal diversity may be inversely related to above-ground biodiversity. [7] [2]

The lack of distinct latitudinal gradients in soil biodiversity contrasts with those clear global patterns observed for plants above ground and has led to the assumption that they are indeed controlled by different factors. [8] For example, in 2007 Lozupone and Knight found salinity was the major environmental determinant of bacterial diversity composition across the globe, rather than extremes of temperature, pH, or other physical and chemical factors. [9] In another global scale study in 2014, Tedersoo et al. concluded fungal richness is causally unrelated to plant diversity and is better explained by climatic factors, followed by edaphic and spatial patterns. [10] Global patterns of the distribution of macroscopic organisms are far poorer documented. However, the little evidence available appears to indicate that, at large scales, soil metazoans respond to altitudinal, latitudinal or area gradients in the same way as those described for above-ground organisms. [11] In contrast, at local scales, the high diversity of microhabitats commonly found in soils provides the required niche portioning to create “hot spots” of diversity in just a gram of soil. [8] [2]

Not only spatial patterns of soil biodiversity are difficult to explain, but also its potential linkages to many soil processes and the overall ecosystem functioning remains under debate. For example, while some studies have found that reductions in the abundance and presence of soil organisms results in the decline of multiple ecosystem functions, [12] others concluded that above-ground plant diversity alone is a better predictor of ecosystem multi-functionality than soil biodiversity. [13] Soil organisms exhibit a wide array of feeding preferences, life-cycles and survival strategies and they interact within complex food webs. [14] Consequently, species richness per se has very little influence on soil processes and functional dissimilarity can have stronger impacts on ecosystem functioning. [15] Therefore, besides the difficulties in linking above and below ground diversities at different spatial scales, gaining a better understanding of the biotic effects on ecosystem processes might require incorporating a great number of components together with several multi-trophic levels  [16] as well as the much less considered non-trophic interactions such as phoresy, passive consumption. [17] ) In addition, if soil systems are indeed self-organized, and soil organisms concentrate their activities within a selected set of discrete scales with some form of overall coordination, [18] there is no need for looking for external factors controlling the assemblages of soil constituents. Instead we might just need to recognize the unexpected and that the linkages between above and below ground diversity and soil processes are difficult to predict. [2]

Microfauna

Recent advances are emerging from studying sub-organism level responses using environmental DNA   [19] and various omics approaches, such as metagenomics, metatranscriptomics, proteomics and proteogenomics, are rapidly advancing, at least for the microbial world. [20] Metaphenomics has been proposed recently as a better way to encompass the omics and the environmental constraints. [21] [2]

Soil food web

An incredible diversity of organisms make up the soil food web. They range in size from the tiniest one-celled bacteria, algae, fungi, and protozoa, to the more complex nematodes and micro-arthropods, to the visible earthworms, insects, small vertebrates, and plants. As these organisms eat, grow, and move through the soil, they make it possible to have clean water, clean air, healthy plants, and moderated water flow.

There are many ways that the soil food web is an integral part of landscape processes. Soil organisms decompose organic compounds, including manure, plant residues, and pesticides, preventing them from entering water and becoming pollutants. They sequester nitrogen and other nutrients that might otherwise enter groundwater, and they fix nitrogen from the atmosphere, making it available to plants. Many organisms enhance soil aggregation and porosity, thus increasing infiltration and reducing surface runoff. Soil organisms prey on crop pests and are food for above-ground animals.

Research

Research interests span many aspects of soil ecology and microbiology, Fundamentally, researchers are interested in understanding the interplay among microorganisms, fauna, and plants, the biogeochemical processes they carry out, and the physical environment in which their activities take place, and applying this knowledge to address environmental problems.

Example research projects are to examine the biogeochemistry and microbial ecology of septic drain field soils used to treat domestic wastewater, the role of anecic earthworms in controlling the movement of water and nitrogen cycle in agricultural soils, and the assessment of soil quality in turf production. [22]

Of particular interest as of 2006 is to understand the roles and functions of arbuscular mycorrhizal fungi in natural ecosystems. The effect of anthropic soil conditions on arbuscular mycorrhizal fungi, and the production of glomalin by arbuscular mycorrhizal fungi are both of particular interest due to their roles in sequestering atmospheric carbon dioxide.

Related Research Articles

<span class="mw-page-title-main">Ecology</span> Study of organisms and their environment

Ecology is the study of the relationships among living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overlaps with the closely related sciences of biogeography, evolutionary biology, genetics, ethology, and natural history.

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

An ecosystem is a system that environments and their organisms form through their interaction. The biotic and abiotic components are linked together through nutrient cycles and energy flows.

<span class="mw-page-title-main">Mycorrhiza</span> Fungus-plant symbiotic association

A mycorrhiza is a symbiotic association between a fungus and a plant. The term mycorrhiza refers to the role of the fungus in the plant's rhizosphere, its root system. Mycorrhizae play important roles in plant nutrition, soil biology, and soil chemistry.

<span class="mw-page-title-main">Food web</span> Natural interconnection of food chains

A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Ecologists can broadly define all life forms as either autotrophs or heterotrophs, based on their trophic levels, the position that they occupy in the food web. To maintain their bodies, grow, develop, and to reproduce, autotrophs produce organic matter from inorganic substances, including both minerals and gases such as carbon dioxide. These chemical reactions require energy, which mainly comes from the Sun and largely by photosynthesis, although a very small amount comes from bioelectrogenesis in wetlands, and mineral electron donors in hydrothermal vents and hot springs. These trophic levels are not binary, but form a gradient that includes complete autotrophs, which obtain their sole source of carbon from the atmosphere, mixotrophs, which are autotrophic organisms that partially obtain organic matter from sources other than the atmosphere, and complete heterotrophs that must feed to obtain organic matter.

<span class="mw-page-title-main">Urban ecology</span> Scientific study of living organisms

Urban ecology is the scientific study of the relation of living organisms with each other and their surroundings in an urban environment. An urban environment refers to environments dominated by high-density residential and commercial buildings, paved surfaces, and other urban-related factors that create a unique landscape. The goal of urban ecology is to achieve a balance between human culture and the natural environment.

<span class="mw-page-title-main">Ecosystem engineer</span> Ecological niche

An ecosystem engineer is any species that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on species richness and landscape-level heterogeneity of an area. As a result, ecosystem engineers are important for maintaining the health and stability of the environment they are living in. Since all organisms impact the environment they live in one way or another, it has been proposed that the term "ecosystem engineers" be used only for keystone species whose behavior very strongly affects other organisms.

The diversity of species and genes in ecological communities affects the functioning of these communities. These ecological effects of biodiversity in turn are affected by both climate change through enhanced greenhouse gases, aerosols and loss of land cover, and biological diversity, causing a rapid loss of biodiversity and extinctions of species and local populations. The current rate of extinction is sometimes considered a mass extinction, with current species extinction rates on the order of 100 to 1000 times as high as in the past.

<span class="mw-page-title-main">Arbuscular mycorrhiza</span> Symbiotic penetrative association between a fungus and the roots of a vascular plant

An arbuscular mycorrhiza (AM) is a type of mycorrhiza in which the symbiont fungus penetrates the cortical cells of the roots of a vascular plant forming arbuscules. Arbuscular mycorrhiza is a type of endomycorrhiza along with ericoid mycorrhiza and orchid mycorrhiza .They are characterized by the formation of unique tree-like structures, the arbuscules. In addition, globular storage structures called vesicles are often encountered.

<span class="mw-page-title-main">Ecosystem service</span> Benefits provided by healthy nature, forests and environmental systems

Ecosystem services are the many and varied benefits to humans provided by the natural environment and healthy ecosystems. Such ecosystems include, for example, agroecosystems, forest ecosystem, grassland ecosystems, and aquatic ecosystems. These ecosystems, functioning in healthy relationships, offer such things as natural pollination of crops, clean air, extreme weather mitigation, and human mental and physical well-being. Collectively, these benefits are becoming known as ecosystem services, and are often integral to the provision of food, the provisioning of clean drinking water, the decomposition of wastes, and the resilience and productivity of food ecosystems.

<span class="mw-page-title-main">Aquatic ecosystem</span> Ecosystem in a body of water

An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic ; lotic ; and wetlands.

<span class="mw-page-title-main">Functional ecology</span>

Functional ecology is a branch of ecology that focuses on the roles, or functions, that species play in the community or ecosystem in which they occur. In this approach, physiological, anatomical, and life history characteristics of the species are emphasized. The term "function" is used to emphasize certain physiological processes rather than discrete properties, describe an organism's role in a trophic system, or illustrate the effects of natural selective processes on an organism. This sub-discipline of ecology represents the crossroads between ecological patterns and the processes and mechanisms that underlie them. It focuses on traits represented in large number of species and can be measured in two ways – the first being screening, which involves measuring a trait across a number of species, and the second being empiricism, which provides quantitative relationships for the traits measured in screening. Functional ecology often emphasizes an integrative approach, using organism traits and activities to understand community dynamics and ecosystem processes, particularly in response to the rapid global changes occurring in earth's environment.

<span class="mw-page-title-main">River ecosystem</span> Type of aquatic ecosystem with flowing freshwater

River ecosystems are flowing waters that drain the landscape, and include the biotic (living) interactions amongst plants, animals and micro-organisms, as well as abiotic (nonliving) physical and chemical interactions of its many parts. River ecosystems are part of larger watershed networks or catchments, where smaller headwater streams drain into mid-size streams, which progressively drain into larger river networks. The major zones in river ecosystems are determined by the river bed's gradient or by the velocity of the current. Faster moving turbulent water typically contains greater concentrations of dissolved oxygen, which supports greater biodiversity than the slow-moving water of pools. These distinctions form the basis for the division of rivers into upland and lowland rivers.

<span class="mw-page-title-main">Soil biology</span> Study of living things in soil

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.

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

Soil quality refers to the condition of soil based on its capacity to perform ecosystem services that meet the needs of human and non-human life.

<span class="mw-page-title-main">Community (ecology)</span> Associated populations of species in a given area

In ecology, a community is a group or association of populations of two or more different species occupying the same geographical area at the same time, also known as a biocoenosis, biotic community, biological community, ecological community, or life assemblage. The term community has a variety of uses. In its simplest form it refers to groups of organisms in a specific place or time, for example, "the fish community of Lake Ontario before industrialization".

Soil biodiversity refers to the relationship of soil to biodiversity and to aspects of the soil that can be managed in relative to biodiversity. Soil biodiversity relates to some catchment management considerations.

In ecology, the term productivity refers to the rate of generation of biomass in an ecosystem, usually expressed in units of mass per volume per unit of time, such as grams per square metre per day. The unit of mass can relate to dry matter or to the mass of generated carbon. The productivity of autotrophs, such as plants, is called primary productivity, while the productivity of heterotrophs, such as animals, is called secondary productivity.

<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">Mycoplankton</span> Fungal members of the plankton communities of aquatic ecosystems

Mycoplankton are saprotrophic members of the plankton communities of marine and freshwater ecosystems. They are composed of filamentous free-living fungi and yeasts that are associated with planktonic particles or phytoplankton. Similar to bacterioplankton, these aquatic fungi play a significant role in heterotrophicmineralization and nutrient cycling. Mycoplankton can be up to 20 mm in diameter and over 50 mm in length.

<span class="mw-page-title-main">Tropical Wet Forests (US and Mexico)</span>

The Tropical Wet Forests are a Level I ecoregion of North America designated by the Commission for Environmental Cooperation (CEC) in its North American Environmental Atlas. As the CEC consists only of Mexico, the United States, and Canada, the defined ecoregion does not extend outside these countries to Central America nor the Caribbean.

References

  1. ↑ Access Science: Soil Ecology Archived 2007-03-12 at the Wayback Machine . Url last accessed 2006-04-06
  2. 1 2 3 4 5 6 7 8 Briones, Maria J. I. (2018). "The Serendipitous Value of Soil Fauna in Ecosystem Functioning: The Unexplained Explained". Frontiers in Environmental Science. 6. doi: 10.3389/fenvs.2018.00149 . CC-BY icon.svg Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
  3. ↑ Lin, Hangsheng; Wheeler, Dan; Bell, Jay; Wilding, Larry (2005). "Assessment of soil spatial variability at multiple scales". Ecological Modelling. 182 (3–4): 271–290. doi:10.1016/j.ecolmodel.2004.04.006.
  4. ↑ Wall, Diana H. (14 June 2012). Soil Ecology and Ecosystem Services. ISBN   978-0-19-957592-3.
  5. 1 2 Nielsen, Uffe N.; Osler, Graham H. R.; Campbell, Colin D.; Neilson, Roy; Burslem, David F. R. P.; Van Der Wal, René (2010). "The Enigma of Soil Animal Species Diversity Revisited: The Role of Small-Scale Heterogeneity". PLOS ONE. 5 (7): e11567. Bibcode:2010PLoSO...511567N. doi: 10.1371/journal.pone.0011567 . PMC   2903492 . PMID   20644639.
  6. ↑ Berg, Matty P.; Bengtsson, Janne (2007). "Temporal and spatial variability in soil food web structure". Oikos. 116 (11): 1789–1804. doi:10.1111/j.0030-1299.2007.15748.x.
  7. ↑ Wu, T.; Ayres, E.; Bardgett, R. D.; Wall, D. H.; Garey, J. R. (2011). "Molecular study of worldwide distribution and diversity of soil animals". Proceedings of the National Academy of Sciences. 108 (43): 17720–17725. Bibcode:2011PNAS..10817720W. doi: 10.1073/pnas.1103824108 . PMC   3203765 . PMID   22006309.
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  9. ↑ Berg, Matty P.; Bengtsson, Janne (2007). "Temporal and spatial variability in soil food web structure". Oikos. 116 (11): 1789–1804. doi:10.1111/j.0030-1299.2007.15748.x.
  10. ↑ Tedersoo, Leho; et al. (2014). "Global diversity and geography of soil fungi" (PDF). Science. 346 (6213). doi:10.1126/science.1256688. PMID   25430773. S2CID   206559506.
  11. ↑ Decaëns, Thibaud (2010). "Macroecological patterns in soil communities". Global Ecology and Biogeography. 19 (3): 287–302. doi: 10.1111/j.1466-8238.2009.00517.x .
  12. ↑ Wagg, C.; Bender, S. F.; Widmer, F.; Van Der Heijden, M. G. A. (2014). "Soil biodiversity and soil community composition determine ecosystem multifunctionality". Proceedings of the National Academy of Sciences. 111 (14): 5266–5270. Bibcode:2014PNAS..111.5266W. doi: 10.1073/pnas.1320054111 . PMC   3986181 . PMID   24639507.
  13. ↑ Jing, Xin; Sanders, Nathan J.; Shi, Yu; Chu, Haiyan; Classen, Aimée T.; Zhao, Ke; Chen, Litong; Shi, Yue; Jiang, Youxu; He, Jin-Sheng (2015). "The links between ecosystem multifunctionality and above- and belowground biodiversity are mediated by climate". Nature Communications. 6: 8159. Bibcode:2015NatCo...6.8159J. doi:10.1038/ncomms9159. PMC   4569729 . PMID   26328906. S2CID   10933025.
  14. ↑ Briones, Marãa Jesãºs I. (2014). "Soil fauna and soil functions: A jigsaw puzzle". Frontiers in Environmental Science. 2. doi: 10.3389/fenvs.2014.00007 .
  15. ↑ Heemsbergen, D. A.; Berg, M. P.; Loreau, M.; Van Hal, J. R.; Faber, J. H.; Verhoef, H. A. (2004). "Biodiversity Effects on Soil Processes Explained by Interspecific Functional Dissimilarity". Science. 306 (5698): 1019–1020. Bibcode:2004Sci...306.1019H. doi:10.1126/science.1101865. PMID   15528441. S2CID   39362502.
  16. ↑ Scherber, Christoph; et al. (2010). "Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment" (PDF). Nature. 468 (7323): 553–556. Bibcode:2010Natur.468..553S. doi:10.1038/nature09492. PMID   20981010. S2CID   4304004.
  17. ↑ Goudard, Alexandra; Loreau, Michel (2008). "Nontrophic Interactions, Biodiversity, and Ecosystem Functioning: An Interaction Web Model". The American Naturalist. 171 (1): 91–106. doi:10.1086/523945. PMID   18171154. S2CID   5120077.
  18. ↑ Lavelle, Patrick; Spain, Alister; Blouin, Manuel; Brown, George; Decaëns, Thibaud; Grimaldi, Michel; Jiménez, Juan José; McKey, Doyle; Mathieu, Jérôme; Velasquez, Elena; Zangerlé, Anne (2016). "Ecosystem Engineers in a Self-organized Soil". Soil Science. 181 (3/4): 91–109. Bibcode:2016SoilS.181...91L. doi:10.1097/SS.0000000000000155. S2CID   102056683.
  19. ↑ Thomsen, Philip Francis; Willerslev, Eske (2015). "Environmental DNA – an emerging tool in conservation for monitoring past and present biodiversity". Biological Conservation. 183: 4–18. doi: 10.1016/j.biocon.2014.11.019 . S2CID   27384537.
  20. ↑ Nannipieri, Paolo (2014). "Soil as a Biological System and Omics Approaches". EQA - International Journal of Environmental Quality. 13: 61–66. doi:10.6092/issn.2281-4485/4541.
  21. ↑ Jansson, Janet K.; Hofmockel, Kirsten S. (2018). "The soil microbiome — from metagenomics to metaphenomics". Current Opinion in Microbiology. 43: 162–168. doi: 10.1016/j.mib.2018.01.013 . PMID   29454931. S2CID   3377418.
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