data in support of research on

1. Nitrogen (N) is an essential nutrient that limits plant growth in many ecosystems. Here we investigate an overlooked component of the terrestrial N cycle—subsurface ammonia (NH3) gas transport and its contribution to plant and mycorrhizal N acquisition.
2. We used controlled mesocosms, soil incubations, stable isotopes, and imaging to investigate edaphic drivers of NH3 gas efflux, track lateral subsurface N transport originating from 15NH3 gas or 15N-enriched organic matter, and assess plant and mycorrhizal N assimilation from this gaseous transport pathway.
3. NH3 is released from soil organic matter, travels below ground, and contributes to root and fungal N content. Abiotic soil properties (pH and texture) influence the quantity of NH3 available for subsurface transport. Mutualisms with arbuscular mycorrhizal (AM) fungi can substantially increase plant NH3-N uptake. The grass Brachypodium distachyon acquired 6-9% of total plant N from organic matter-N that traveled as a gas below ground. Colonization by the AM fungus Rhizophagus irregularis was associated with a twofold increase in total plant N acquisition from subsurface NH3 gas.
4. NH3 gas transport and uptake pathways may be fundamentally different from those of more commonly studied soil N species and warrant further research.