Photo sources:
1. http://botit.botany.wisc.edu/toms_fungi/oct98.html
   http://davesgarden.com/guides/articles/view/1936/;
   R. Campbell. In R. Campbell. 1985. Plant Microbiology;
   http://www.today-archive.colostate.edu/index.asp?url=display_story&story_id=1005761
2. Map by Philippe Rekacewicz, UNEP/GRID-Arendal; data from International Permafrost Association, 1998. Circumpolar Active-Layer Permafrost System (CAPS), version 1.0.
3. Adrien C Finzi, Jonathan J Cole, Scott C Doney, Elisabeth A Holland, and Robert B Jackson 2011. Research frontiers in the analysis of coupled biogeochemical cycles. Frontiers in Ecology and the Environment 9: 74¨C80. http://dx.doi.org/10.1890/100137