The Syringe Pump Gas Distribution (SPGD) system: a simple and low-cost method for simulating NH₃/¹⁵NH₃ deposition

Ammonia (NH₃) in the atmosphere plays a crucial role in the global nitrogen cycle. Elevated NH₃ deposition can result in various detrimental ecological and environmental consequences. Traditionally, researchers have employed methods such as static fumigation, dynamic fumigation using high-precision mass flow meters or standard gas cylinders, and free air enrichment to investigate vegetation responses to NH₃ deposition. However, these approaches may suffer from inaccuracies, high costs, or technical complexity. In order to address this issue, we developed the Syringe Pump Gas Distribution (SPGD) system, a cost-effective new method for simulating NH₃/¹⁵NH₃ deposition. This system allows for precise and stable mixing of NH₃/¹⁵NH₃ stored in a syringe with air using a microinjection pump. The resulting mixture is then utilized to simulate NH₃/¹⁵NH₃ deposition. With just one 20 ml syringe, a single SPGD system can simulate NH₃ deposition flux ranging from 0 to 31.74 mg N m^-2 d^-1 (equivalent to 0 - 116 kg N ha^-1 yr^-1) over an area of 0.36 m². The SPGD system demonstrated reliability and stability during a 21-day simulated deposition test on potted Populus cathayana under greenhouse conditions (including simulated rainfall). It exhibited adequate adjustment resolution to generate environments with varying NH₃ concentrations, corresponding to different NH₃ deposition fluxes. The test findings indicated a positive correlation between the δ₁₅N levels in P. cathayana leaves and the NH₃ deposition flux increase. The cost, complexity, and risk associated with simulating NH₃ deposition can be significantly decreased by utilizing the SPGD system. The SPGD system is modular (gas supply unit and NH₃ supply unit) and can be adapted to different research needs, including for simulating the deposition of NO₂, SO₂ or mixtures. Adopting this system, researchers can safely and efficiently simulate NH₃ deposition or perform ¹⁵NH₃ labeling, thereby advancing the understanding of physiological and ecological processes associated with plants and even forest ecosystems under gaseous deposition.