Forest ecosystems carbon cycling

Under low-dose conditions, forest ecosystems act as sinks for atmospheric pollutants and in some instances as sources. As indicated in Chapter 7, the atmosphere, lithosphere, and oceans are involved in cycling carbon, nitrogen, oxygen, sulfur, and other elements through each subsystem with different time scales. Under low-dose conditions, forest and other biomass systems have been utilizing chemical compounds present in the atmosphere and releasing others to the atmosphere for thousands of years. Industrialization has increased the concentrations of NO2, SO2, and CO2 in the "clean background" atmosphere, and certain types of interactions with forest systems can be defined. 

Sedjo, R. A. (1992). Temperate forest ecosystems in the global carbon cycle, Ambio, 21, 274-277. 

Soil contributes to a greater extent to total carbon storage than do above-ground vegetation in most forests (Johnson and Curtis 2001). The total amount of soil organic carbon (SOC) in the upper meter of soil is about 1500 x 1015 g C (Eswaran et al. 1993 Batjes 1996), and the global atmospheric pool of CO2 is about 750 x 1015 g C (Harden et al. 1992). The CO2 emission from soil into atmosphere is about 68.0-76.5 1015 g C per year, and this is more than 10 times the CO2 released from fossil fuel combustion (Raich and Potter 1995). Variations in SOC pools and SOM turnover rates, therefore, exert substantial impacts on the carbon cycles of terrestrial ecosystems in terms of carbon sequestration in soil and CO2 emission from soil. 

Figure 6. Carbon bio geochemical cycle in the hypothec forest ecosystem (Schulze, 2000). 

Schulze, E-D. (2000). Carbon and nitrogen cycling in European forest ecosystems. Berlin Springer, 500 p. 

Including food-web processes in quantitative models of carbon and nitrogen cycling of forest ecosystems. The competition between sapro-trophic and mycorrhizal fungi for resources is a key aspect of belowground functioning (Lindahl et al., 2002). Quite detailed computer models... 

Wallenda, T., Stober, C., Hogbom, L. et al. (2000). Nitrogen uptake processes in roots and mycorrhizas. In Carbon and Nitrogen Cycling in European Forest Ecosystems, Ecological Studies 142, ed. E. D. Schulze. Berlin Springer-Verlag, pp. 122-43. 

Flanagan L. B., Brooks J. R., Varney G. T., Berry S. C., and Ehleringer . R. (1996) Carbon isotope discrimination during photosynthesis and the isotope ratio of respired CO2 in boreal forest ecosystems. Global Biogeochem. Cycles 10(4), 629-640. 

This comparison points out a fundamental difference between the two ecosystems in the context of the global carbon cycle. On timescales of decades to centuries, carbon fixed in terrestrial ecosystems can be temporarily stored in organic matter (e.g., forests), whereas most of the carbon fixed by... 

Houghton, R. A. (1996). Land-use change and terrestrial carbon The temporal record. In Forest Ecosystems, Forest Management and the Global Carbon Cycle" (M, J, Apps and D. T. Price, Ed.), pp. 117- 134. NATO ASI Series, Springer-Verlag, Berlin, Heidelberg. 

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