Increasing Precipitation Intensity and N Addition Interactively Affect Soil Respiration and N2O Fluxes in Grassland

Precipitation intensity and nitrogen (N) deposition are projected to increase under global change scenarios, and both are expected to affect greenhouse gas (GHG) fluxes. However, the interactive effects of increasing precipitation intensity and N addition on GHG fluxes are still unknown. To address this gap, a mesocosm simulation experiment was conducted to investigate the individual and combined effects of changing precipitation intensity (with a constant event magnitude of 50 mm) and long-term N addition on GHG fluxes. The results revealed that precipitation application triggered a pulse effect on GHG fluxes, with increases up to 876% compared to pre-precipitation levels. The net changes in water-filled pore spaces (Δ WFPS) affected the temporal dynamics of GHG fluxes. Increasing precipitation intensity suppressed cumulative soil respiration, methane uptake, and nitrous oxide fluxes by directly reducing water availability (WFPS) and indirectly suppressing microbial biomass and substrate availability (dissolved organic carbon (DOC) or nitrate N content (NO₃⁻-N)). Furthermore, precipitation application altered the magnitude or direction of GHG flux responses to N addition. Changes in precipitation intensity and N addition had interactive effects on the Δ cumulative soil respiration and Δ cumulative N₂O fluxes, but not on Δ cumulative CH₄ fluxes. Increasing precipitation intensities decreased the Δ DOC content in the unfertilized treatment and increased Δ DOC content in the N addition treatment, thereby interactively affecting Δ cumulative soil respiration. N addition increased the Δ NO₃⁻-N content, influencing the response of Δ cumulative N₂O fluxes to increasing precipitation intensities. Our findings highlight that precipitation intensity regulates grassland GHG with N interactions, providing mechanistic insights to refine climate feedback predictions in ecosystems.