Nitrogen cycling boreal forests

Since nitrogen is a nutrient, which limits the productivity of almost all Boreal and Sub-Boreal Forest ecosystems, its biogeochemical cycling is relatively well understood at present. The major N transformations and fluxes are shown in Figure 3. 

Tamm, C. O. (1982). Nitrogen cycling in undisturbed and manipulated boreal forest. 

But the dogma also has it that tropical forests are usually found on heavily weathered soils that are low in nutrients, particularly phosphorus. In a manner similar to possible interactions between the nitrogen and carbon cycles in temperate and boreal forests (McGuire et al., 1995) it has thus been suggested that low P availability may limit the extent to which tropical forests are able to increase their productivity in response to increases in atmospheric CO2 concentrations (Friedlingstein et al, 1995 McKane et al., 1995). 

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