Ecosystems acquire nitrogen from the atmosphere, but this source can't account for the large nitrogen capital of some systems. The finding that bedrock can also act as a nitrogen source may help solve the riddle.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/nitrogen-deep
[2] http://admin.indiaenvironmentportal.org.in/category/author/edward-g-schuur
[3] http://admin.indiaenvironmentportal.org.in/category/journal/nature
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/atmosphere-and-ozone-layer
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/oxides-nitrogen-nox
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/ecosystems
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/flora
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/forests
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/california