What are the differences between tundra and taiga in regards to soil characteristics

Tundra soils are formed at high latitudes. It is usually very cold in the tundra. Tundra soils are generally frozen, and are classifed as Gelisols (think Gelato!).   In order to be a Gelisol, permafrost needs to be within 100 cm of the soil surface. These soils freeze and thaw a lot, making the soil heave and buckle (cryoturbation), like a mixter does to cookie dough. This creates trees at funny angles , and can generate a lot of building issues. 

The soil quality of a taiga biome is very poor. This poor quality is due to the fact that the taiga has such low temperatures  for such a long period of time. Fallen leaves and moss can remain on the floor for a long time without decomposing due to the cold, moist climate. This limits their organic contribution to the soil, creating spodosol. This in turn limits the ground coverage of the forest floor.