User:AOpland/Denitrification

Potential gaps in knowledge:


 * Factors that lead to partial denitrification (temperature, pH), possibly mention in introduction with respect to N2O leakage
 * Broad ecological significance (N2O production, conversion of nitrogen)

Format something like:

Paragraph 1: Conditions that affect denitrification on a general level

Paragraph 2: Conditions that affect complete vs partial denitrification, possible mention to N2O leakage as a greenhouse gas.

Article body
( Base Article)

In nature, denitrification can take place in both terrestrial and marine ecosystems. Typically, denitrification occurs in anoxic environments, where the concentration of dissolved and freely available oxygen is depleted. In these areas, nitrate (NO3−) or nitrite (NO2−) can be used as a substitute terminal electron acceptor instead of oxygen (O2), a more energetically favourable electron acceptor. Terminal electron acceptor is a compound that gets reduced in the reaction by receiving electrons. Examples of anoxic environments can include soils, groundwater, wetlands, oil reservoirs, poorly ventilated corners of the ocean and seafloor sediments.

Furthermore, denitrification can occur in oxic environments as well. High activity of denitrifiers can be observed in the intertidal zones, where the tidal cycles cause fluctuations of oxygen concentration in sandy coastal sediments. For example, the bacterial species Paracoccus denitrificans engages in denitrification under both oxic and anoxic conditions simultaneously. Upon oxygen exposure, the bacteria is able to utilize nitrous oxide reductase, an enzyme that catalyzes the last step of denitrification. Aerobic denitrifiers are mainly Gram-negative bacteria in the phylum Proteobacteria. Enzymes NapAB, NirS, NirK and NosZ are located in the periplasm, a wide space bordered by the cytoplasmic and the outer membrane in Gram-negative bacteria.

'''A variety of environmental factors can influence the rate of denitrification on an ecosystem-wide scale. For example, temperature and pH have been observed to impact denitrification. In bacterial species Pseudomonas mandelii, expression of denitrifying genes was reduced at temperatures below 30°C and a pH below 5, while activity was largely unaffected between a pH of 6-8. Organic carbon as an electron donor is a common limiting nutrient for denitrification as observed in benthic sediments and wetlands. Nitrate and oxygen can also be a potential limiting factors for denitrification,  although the latter only has an observed limiting effect in wet soils.''' Oxygen likely affects denitrification multiple ways--because most denitrifiers are facultative, oxygen can inhibit rates, but it can also stimulate denitrification by facilitating nitrification and the production of nitrate. In wetlands as well as deserts, moisture is an environmental limiter on rates of denitrification.

'''Environmental factors can also influence whether denitrification proceeds to completion, characterized by the complete reduction of NO3- to N2 rather than releasing N2O as an end product. Soil pH and texture are both factors that can moderate denitrification, with higher pH levels driving the reaction more to completion. Nutrient composition, particularly the ratio of carbon to nitrogen, is a strong contributor to complete denitrification, with a 2:1 ratio of C:N being able to facilitate full nitrate reduction regardless of temperature or carbon source. Copper, as a co-factor for nitrite reductase and nitrous-oxide reductase, also promoted complete denitrification when added as a supplement. Besides nutrients and terrain, microbial community composition can also affect the ratio of complete denitrification, with prokaryotic phyla Actinomycetota and Thermoproteota being responsible for greater release of N2 than N2O compared to other prokaryotes.'''

Denitrification can contribute to isotopic fractionation in the soil environment. The two stable isotopes of nitrogen, 14N and 15N are both found in the sediment profiles. The lighter isotope of nitrogen, 14N, is preferred during denitrification, leaving the heavier nitrogen isotope, 15N, in the residual matter. This selectivity leads to the enrichment of 14N in biomass compared to 15N. Moreover, the relative abundance of 14N can be analyzed to distinguish denitrification apart from other processes in nature.