Impact of water on microbial nitrogen transformation in soil causing atmospheric nitrous acid (HONO) and nitric oxide (NO) emissions

Abstract

Biological soil crusts (referred to as biocrusts hereafter) represent communities comprising a fraction of photoautotrophs (photoautotrophic bacteria, algae, lichens, and bryophytes) growing together with heterotrophic organisms like bacteria, archaea, and fungi. The organisms are all poikilohydric, which means they are only active if water is present. They occur frequently in dryland ecosystems, where vascular vegetation is sparse or even absent, or wherever dry microclimatic conditions occur. Biocrusts fulfill a wide range of important ecosystem services, as they are relevant in regional water cycling, soil stabilization, plant germination and growth, and also global carbon (C) and nitrogen (N) cycling. According to initial estimates, they are supposed to globally emit ~1.7 Tg of reactive nitrogen (N r ) per year, corresponding to ~20% of the global nitrogen oxide emissions from soils under natural vegetation. The underlying mechanisms of N r