Carbon compounds soil respiration

Sometimes the risk of waste is estimated on the basis of nutrient cycling tests. As a rule such investigation is carried out for surface waste disposal or its land application. The carbon cycle is very sensitive to harmful compounds. Soil respiration is considered a useful indicator of the contaminants effects on soil microbial activity [56-59]. The production of carbon dioxide can be followed as short-term and long-term respiration tests. 

The carbon we do not see do low molecular weight compounds have a significant impact on carbon dynamics and respiration in forest soils Soil Biology and Biochemistry, 37, 1-13. 

Plants can absorb soil NH3 or NH4 directly and some microorganisms, such as Nitrosomonas, oxidize NH3, using it as an energy source for respiration, in the same way that other cells use reduced carbon compounds. One possible reaction would be ... 

One of the largest natural carbon flows through the environment is driven by photosynthesis. Plants take up CO2 and water and turn them into reduced carbon compounds such as starch and cellulose. Photosynthesis fixes about 100 GtC per year. Most of this is returned via respiration and decomposition, but it seems that over the last decade, mid-latitude forests have been net sinks for C02. Trees and other plants sequester CO2 during periods of growth. Thus, forestation and agricultural fixation of carbon, in either biomass or soil carbon, can play a role in carbon... 

Carbon Dioxide - A colorless, odorless noncombustible gas with the formula C02 that is present in the atmosphere. It is formed by the combustion of carbon and carbon compounds (such as fossil fuels and biomass), by respiration, which is a slow combustion in animals and plants, and by the gradual oxidation of organic matter in the soil. 

Root products, as defined by Uren and Reisenauer (17), represent a wide range of compounds. Only secretions are deemed to have a direct and immediate functional role in the rhizosphere. Carbon dioxide, although labeled an excretion, may play a role in rhizosphere processes such as hyphal elongation of vesicular-arbuscular mycorrhiza (39). Also, root-derived CO2 may have an effect on nonphotosynthetic fixation of CO2 by roots subject to P deficiency and thus contribute to exudation of large amounts of citrate and malate, as observed in white lupins (40). The amounts utilized are very small and, in any case, are extremely difficult to distinguish from endogenous CO2 derived from soil and rhizosphere respiration. 

The compounds that we will consider here, in contrast, serve quite specific needs of various organisms, and for this reason we will call them special chemical compounds. Different species may employ the same special compound, in some cases for the same purpose and in other cases for different ends. For example, the carbon dioxide arising from the respiration of a crowd of ants is an aggregation signal that invites solitary ants to join their nestmates. Corn rootworms, however, use the carbon dioxide that living corn roots emit into the soil as a signal, leading them to their food. Different species may also employ diverse compounds for essentially the same purpose. Various ant species mark their food trails with different chemicals to keep their food sources secret from one another. 

Aside from adding defined compounds, experimental additions of natural DOM mixtures suspected to vary in lability have helped test ideas about the contribution of various DOM sources to aquatic ecosystems. In a nice example using manipulation of natural DOM sources, Battin et al. (1999) used flowthrough microcosms to measure the relative uptake rates of allochthonous and autochthonous DOM by stream sediments. They documented greater than fivefold differences or more in uptake and respiration, depending on whether the DOM was extracted from soil or periphyton. Moreover, they were able to show, via transplant experiments, several cases where prior exposure to a particular source of DOM increased the ability of that community to metabolize the DOM supplied. There appears to be some preadaptation of microbial catabolic capacity when these stream biofilms were re-exposed to a familiar type of DOM. Similarly, the response of heterotrophic bacteria to carbon or nutrient addition was greatest when the source community was particularly active (Foreman et al., 1998). Kaplan et al. (1996) showed that fixed film bioreactors, colonized on one water source, were unable to rapidly metabolize DOC in water from another source. 

NPP is the net carbon gain by vegetation over a particular time period— typically a year. It is the balance between the carbon gained by photosynthesis and the carbon released by plant respiration. NPP includes the new biomass produced by plants, the soluble organic compounds that diffuse or are secreted by roots into the soil (root exudation), the carbon transfers to microbes that are symbiotically associated with roots (e.g., mycorrhizae and nitrogen-fixing bacteria), and the volatile emissions that are lost from leaves to the atmosphere (Clark et al., 2001). 

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