Particulate organic matter

Particulate organic matter (POM, macroorganic matter, or coarse fraction organic matter) is defined as organic particles such as soil organic matter or other particulates between 0.053 mm and 2 mm in size.[1][2] Isolated by sieving or filtration, this fraction includes partially decomposed detritus and plant material, pollen, and other materials.[3][4] When sieving to determine POM content, consistency is crucial because isolated size fractions will depend on the force of agitation.[2]

POM is readily decomposable, serving many soil functions and providing terrestrial material to water bodies. It is a source of food for both soil organisms and aquatic organisms (see below), and provides nutrients for plants. In water bodies, POM can contribute substantially to turbidity, limiting photic depth which can suppress primary productivity. POM also enhances soil structure leading to increased water infiltration, aeration and resistance to erosion [3][5] Soil management practices, such as tillage and compost/manure application, alter the POM content of soil and water.[3][4]

Role in the lower aquatic food web

Along with dissolved organic matter, POM drives the lower aquatic food web by providing energy in the form of carbohydrates, sugars, and other polymers that can be degraded. POM in water bodies is derived from terrestrial inputs (e.g. soil organic matter, leaf litterfall), submerged or floating aquatic vegetation, or autochthonous production of algae (living or detrital). Each source of POM has its own chemical composition that affects its lability, or accessibility to the food web. Algal-derived POM is thought to be most labile, but there is growing evidence that terrestrially-derived POM can supplement the diets of micro-organisms such as zooplankton when primary productivity is limited.[6][7]

Role in soil function

The decomposition of POM provides energy and nutrients. Nutrients not taken up by soil organisms may be available for plant uptake.[4] The amount of nutrients released (mineralized) during decomposition depends on the biological and chemical characteristics of the POM, such as the C:N ratio.[4] In addition to nutrient release, decomposers colonizing POM play a role in improving soil structure.[8] Fungal mycelium entangle soil particles and release sticky, cement-like, polysaccharides into the soil; ultimately forming soil aggregates [8]

Effect of soil management

Soil POM content is affected by organic inputs and the activity of soil decomposers. The addition of organic materials, such as manure or crop residues, typically results in an increase in POM.[4] Alternatively, repeated tillage or soil disturbance increases the rate of decomposition by exposing soil organisms to oxygen and organic substrates; ultimately, depleting POM. Reduction in POM content is observed when native grasslands are converted to agricultural land.[3] Soil temperature and moisture also affect the rate of POM decomposition.[4] Because POM is a readily available (labile) source of soil nutrients, is a contributor to soil structure, and is highly sensitive to soil management, it is frequently used as an indicator to measure soil quality.[5]

Surface water contamination

In poorly-managed soils, particularly on sloped ground, erosion and transport of soil sediment rich in POM can contaminate water bodies.[5] Because POM provides a source of energy and nutrients, rapid build-up of organic matter in water can result in eutrophication.[8] Suspended organic materials can also serve as a potential vector for the pollution of water with fecal bacteria, toxic metals or organic compounds.

See also
  • Particulate matter

References
  1. Cambardella, C. A.; Elliott, E. T. (1991). "Particulate soil organic-matter changes across a grassland cultivation sequence". Soil Science Society of America Journal. 56 (3): 777–783. doi:10.2136/sssaj1992.03615995005600030017x.
  2. Carter, M. R. (1993). Soil Sampling and Methods of Analysis. CRC Press.
  3. Brady, N. C.; Weil, R. R. (2007). The nature and properties of soils (11th ed.). Upper Saddle River, NJ: Prentice-Hall Inc.
  4. Gregorich, E. G.; Beare, M. H.; McKim, U. F.; Skjemstad, J. O. (2006). "Chemical and biological characteristics of physically uncomplexed organic matter". Soil Science Society of America Journal. 70 (3): 975–985. doi:10.2136/sssaj2005.0116.
  5. "Particulate Organic Matter". Soil quality for environmental health. NRCS.
  6. Weidel, Brian; Solomon, Christopher T.; Pace, Michael L.; Kitchell, Jim; Carpenter, Stephen R.; Cole, Jonathan J. (2011-02-01). "Strong evidence for terrestrial support of zooplankton in small lakes based on stable isotopes of carbon, nitrogen, and hydrogen". Proceedings of the National Academy of Sciences. 108 (5): 1975–1980. doi:10.1073/pnas.1012807108. ISSN 0027-8424. PMC 3033307. PMID 21245299.
  7. Kankaala, Paula; Strandberg, Ursula; Kimmo K. Kahilainen; Aalto, Sanni L.; Galloway, Aaron W. E.; Taipale, Sami J. (2016-08-11). "Terrestrial carbohydrates support freshwater zooplankton during phytoplankton deficiency". Scientific Reports. 6: 30897. doi:10.1038/srep30897. ISSN 2045-2322. PMC 4980614. PMID 27510848.
  8. Six, J.; Bossuyt, H.; Degryze, S; Denef, K (2004). "A history of research on the link between (micro) aggregates, soil biota, and soil organic matter dynamics". Soil and Tillage Research. 79 (1): 7–31. doi:10.1016/j.still.2004.03.008.
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