Pathways of Nitrogen Loss After Fertilization in Dryland Ecosystems

Dryland ecosystems cover approximately 41% of the Earth’s terrestrial surface, and are characterized by limited moisture, nutrient-poor soils, and pulsed precipitation regimes that collectively constrain nutrient cycling. Although nitrogen (N) is often assumed to be a primary limiting nutrient in these environments, fertilization studies frequently reveal minimal biotic response to added N—a pattern known as the "dryland nitrogen paradox." This paradox has been attributed to rapid nitrogen loss via gaseous emissions and leaching, exacerbated by interactions with water and phosphorus (P) availability. To investigate these loss pathways, we conducted a field experiment at the Jornada Experimental Range in the northern Chihuahuan Desert using a factorial design of N, P, and water (W) additions. We quantified nitrogen loss during the 2024 monsoon season through both short-term gas fluxes (using a T200UP NO/NO2 Analyzer) and cumulative fluxes (using Ogawa passive samplers), as well as nutrient leaching via ion exchange resins. Our results show that nitrogen additions significantly increased gaseous N emissions (NOₓ, NH₃) and nitrate leaching, with prolonged fluxes observed weeks after fertilization. While phosphorus alone had limited effects, N×P interactions notably influenced NH₃ emissions and phosphate retention. Water additions amplified nitrate leaching under nitrogen treatments but did not significantly alter cumulative gaseous fluxes. These findings demonstrate that nutrient loss in drylands is temporally dynamic, context-dependent, and driven by co-limiting factors. Our work reinforces the need for integrated nutrient-water management strategies in drylands and contributes to a broader understanding of nitrogen cycling under global change.