Particulate organic matter is defined as organic particles such as soil organic matter or other particulates between 0.053 mm and 2 mm in size. Isolated by sieving or filtration, this fraction includes partially decomposeddetritus and plant material, pollen, and other materials. When sieving to determine POM content, consistency is crucial because isolated size fractions will depend on the force of agitation. 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, 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 erosionSoil management practices, such as tillage and compost/manure application, alter the POM content of soil and water.
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, submerged or floating aquatic vegetation, or autochthonous production of algae. 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.
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. The amount of nutrients released during decomposition depends on the biological and chemical characteristics of the POM, such as the C:N ratio. In addition to nutrient release, decomposers colonizing POM play a role in improving soil structure. Fungal mycelium entangle soil particles and release sticky, cement-like, polysaccharides into the soil; ultimately forming soil aggregates
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. 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. Soil temperature and moisture also affect the rate of POM decomposition. Because POM is a readily available 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.
