Microbiology

Cryptic N2 Fixation

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Science  27 Jul 2012:
Vol. 337, Issue 6093, pp. 391
DOI: 10.1126/science.337.6093.391-a
CREDITS (TOP AND MIDDLE): BURKHARD BÜDEL; (BOTTOM) BETTINA WEBER

Lichen-covered buildings, rocks, and trees are a common sight. Indeed, if they remain static for long enough, or simply grow slowly, most objects on Earth's surface become coated by cyanobacteria, algae, fungi, lichens, and bryophytes. These coatings are called cryptogamic covers, and Elbert et al. estimate that these photoautotrophic communities make substantial contributions to carbon and nitrogen cycling. Carbon uptake by these communities was estimated to be highest in Europe (at about 10% of net primary production) and lowest in Africa (at about 4%) and in total to constitute about 1% of the carbon content of terrestrial vegetation. Far more striking is their relative contribution to total biological nitrogen fixation, ranging from 30% in Europe and South America to more than 80% in Asia and North America. This means that models of nitrogen cycling need to account for the activities of cryptogamic covers, or they may miss the majority of biological nitrogen fixation occurring in some regions.

Nat. Geosci. 5, 459 (2012).

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