Cryptogamic covers (CC) comprise cyanobacteria, lichens, algae, and bryophytes plus heterotrophic bacteria, fungi, and archaea in varying proportions. Depending on habitat, cryptogamic rock covers, cryptogamic plant covers, and cryptogamic soil covers are distinguished. In a first assessment of their global role, we quantified that CC fix ~49Tg of nitrogen (N) per year, corresponding to ~1/2 of the maximum terrestrial biological N fixation determined in the latest IPCC report. The fixed N is used for biomass formation and partially leached into the ground, where it may be taken up by plants, but it may also be transformed into N oxides, being emitted into the atmosphere. We show that CC release nitrous oxide (N2O), a greenhouse gas of crucial importance for climate change. The emission rates vary with temperature, humidity, and N deposition, but divided by respiratory CO2 emission they form an almost constant ratio, which allows upscaling on the global scale. We estimate annual N2O emissions of 0.32 – 0.59 Tg by CC, accounting for 4-9% of the global N2O budget from natural terrestrial sources. Formation processes and potential emissions of other N oxides by CC will be discussed.