Carbon reservoirs soil organic matter

Humus is a group of organic compounds in terrestrial ecosystems that is not readily decomposed and therefore makes up a carbon reservoir with a long turnover time. There are also significant structural differences between the marine and terrestrial substances (Stuermer and Payne, 1976). The soil organic matter of humus is often separated into three groups similar in structural characteristics but with differing solubility behavior in water solutions. Humic acids, fulvic acids, and humin are... 

From Fig. 6.1 it can be seen that the annual net primary production for land plants and marine plants is similar (c.60 and 40Gt, respectively), although the biomass of terrestrial plants is much greater than that of marine plants. This is an important demonstration of the fact that biomass is not necessarily a guide to productivity. There is another difference between the marine and terrestrial parts of the biochemical subcycle the residence time of C in the main reservoirs. From Fig. 6.1 it can be seen that the residence time of carbon in the terrestrial biota is c.5.5 years (i.e.600/110yr), and c.26 years (1600/60.6 yr) in soil organic matter. In contrast, the residence time of C in marine phyto-planktonic biomass is only c.2 weeks (1.5/40 yr), but c.338 years (39 000/115.3 yr) in oceanic dissolved carbon. 

Among the carbon reservoirs of the biosphere, a large proportion is stored in soil organic matter and marine sediments (Bolin, 1977). The accumulation of carbon in soils and sediments is a function of the organic carbon balance between net primary production (carbon fixation) and heterotro-phic metabolism (decomposition). The fixation of atmospheric carbon through photosynthesis is the major sonrce of carbon to terrestrial, wetland, and aquatic ecosystem. 

The portion of Earth and its atmosphere that can support life. The part (reservoir) of the global carbon cycle that includes living organisms (plants and animals) and life-derived organic matter (litter, detritus). The terrestrial biosphere includes the living biota (plants and animals) and the litter and soil organic matter on land, and the marine biosphere includes the biota and detritus in the oceans. 

Organic matter in soils is the largest carbon reservoir in rapid exchange with atmospheric C02, and thus it is important as a potential source and sink of greenhouse gases over time scales of human concern (Fischlin and Gyalistras, 1997). SOM... 

At the ecosystem scale, the flux of carbon among various reservoirs is a continuous process and follows a steady decay continuum. In a stepwise manner, carbon dioxide fixed during photosynthesis is returned to the atmosphere by the decomposition process, and the undecomposed organic matter is retained in the soil (Figure 5.7). The steps are as follows ... 

In wetlands, diffusive flux of toxic organics associated with colloidal organic matter may also be important. The sediment serves as a reservoir of dissolved organic carbon. Diffusion of toxic organics absorbed to organic carbon compounds into and out of the sediment bed may be an important transport process in highly organic soils. 

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