The Soils and Their Nutrients 221 



Meadow 

 Avg C:N = 20.4 



Rim 

 20.2 



40 20 2 40 20 2 40 20 2 40 20 2 

 Percent Carbon and Nitrogen in the Soil 



10- 



I 20 



30- 



5000 



5000 



g Carbon m (5cm depth) 



r-i ■ 1- 



5000 

 -I 



5000 



FIGURE 7-1. The percentage of carbon and nitrogen 

 in soils from different tundra microtopographic 

 units, including meadows, basins of low-centered 

 polygons, polygon troughs, and rims of low-centered 

 polygons. 



In nearly all the soils, organic matter in the surface horizons is most- 

 ly fibric; the degree of decomposition increases with depth. Fibric organ- 

 ic matter includes slightly decomposed, reddish- to yellowish-brown fib- 

 rous materials whose generic characteristics can be recognized and which 

 are usually interlaced by an abundance of living roots and rhizomes. Live 

 belowground plant parts averaged 660 g m"^ in 1972, most of it in the up- 

 per 10 cm (Dennis et al. 1978). Fibric materials are commonly associated 

 with wet meadow and polygon trough soils, but such materials rarely 

 dominate the entire soil profile. 



Sapric inclusions of black to dark reddish-brown, generically uni- 

 dentifiable, fibrous to granular organic materials which disintegrate 

 completely under the mildest mechanical manipulation are commonly 

 found below the surface horizon. In the better drained, more highly oxi- 

 dized soils such as are found on the tops of high-centered polygons and 

 the rims of low-centered polygons, highly decomposed sapric organic 

 matter may predominate throughout the entire active layer and continue 

 down into the permafrost. 



Hemic materials, those of intermediate decomposition, represent the 

 most common form of organic matter in the soils. These generally range 

 in color from dark grayish-brown to dark brown, and in nearly all cases 



