Global Variations in the SOC Pool

Predictable variations in the SOC pool have been observed in either comparative. studies between soils from contrasting climates (Jenny, 1961 Trumbore, 1993) or contrasting soil textural types (Parton et ai, 1987), transects along climatic gradients (Townsend et ai, 1995), transects acro.ss soil chrono/topo sequences (Goh ct ai, 1976 ), and comparisons between disturbed and undisturbed areas (Townsend et ai, 1995 Desjardin et ai, 1993). In addition, some studies have attempted to look at SOC trends on the continental (e.g., Spain et ai, 1983 Moraes et ai, 1995) or global (e.g., Post et ai, 1982) scale using data compiled from literature sources and have been able to deduce major trends in SOC inventories with respect to climate and soil type, but generally with much scatter in the data. 

From this understanding of the behavior of the SOC pool, models such as Rothamsted (Jenkinson and Rayner, 1977) and Century (Parton et ai, 1993) have been developed that allow results from regional validation studies to be extrapolated to the global scale (Schimel et al, 1994). Such models divide the SOC pool up into three to five pools with turnover times ranging from years to thousands of years, and the sizes of the.se pools for a given. soil texture are determined by climate-driven interactions between plant carbon inputs, nutrients, microbial respiration, and leaching of DOC (Fig. 2). In some cases, the.se models have been tested 

FIGURE 2 Carbon flows in the Century model (Parton et al., 1987). 

TABLE 3 Observational Trends in Soil Carbon Storage 

SOC turnover rates decrease with decreasing temperature (T) and rainfall (ppt) 

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