Atmospheric nitrogen (N) deposition rates affect soil N dynamics, influencing soil respiration (R_S) rates. However, for the Mediterranean region, the effect of changes in atmospheric N deposition on R_S are not well constrained yet. We investigated the interplay between increased N deposition and tree species composition on R_S at a Scots pine—Pyrenean oak ecotone in Central Spain, and whether the observed responses were mediated by changes on selected soil properties. Throughout 3 years, we simulated two N deposition rates—10 (medium) and 40 kg N ha⁻¹ a⁻¹ (high)—over the background deposition (control) in neighbouring stands in which tree species composition (pine or oak) shapes soil stoichiometry and microbial communities. We monitored R_S on a monthly basis during 3 years; in addition, we performed targeted measurements 24 h after the N fertilization events to assess short-term soil responses. During winter and summer, R_S did not respond to enhanced N deposition rates. In spring and autumn, higher R_S rates were observed in the medium-fertilization, but the size and duration of this effect was tree species dependent. We suggest that climate seasonality modulates the response of R_S to N availability, with tree species effects becoming relevant only when environmental conditions are adequate. R_S in fertilized plots was larger from February to May and in September under pine, while under oak a response was observed only in April, probably due to differences in native soil stoichiometry under each tree species. Overall, R_S showed high stability during 3 years of N enrichment in this Mediterranean ecotone area. However, we observed short-term soil responses after N fertilization events—loss of base cations, soil acidification and reduced microbial biomass—which emphasize the need to investigate consequences for the belowground C and N cycles if chronic N enrichment persists in the long run.

大气氮 (N) 沉积率影响土壤氮动态，影响土壤呼吸 (R _S ) 率。然而，对于地中海地区，大气氮沉降变化对 R _S的影响尚未得到很好的限制。我们研究了R上增加N沉降和树种组成之间的相互_小号在中部西班牙欧洲赤松-比利牛斯橡木交错，以及是否观察到的应答通过在选定的土壤性质的变化介导的。在整个 3 年中，我们模拟了两种 N 沉积速率——10（中等）和 40 kg N ha ^-1 a ^-1（高）——在邻近林分的背景沉积（对照）上，其中树种组成（松树或橡树）塑造了土壤化学计量和微生物群落。我们在 3 年内每月对 R _S进行监测；此外，我们在施氮事件后 24 小时进行了有针对性的测量，以评估短期土壤反应。在冬季和夏季，R _S对增加的 N 沉积速率没有反应。在春季和秋季，在中等施肥中观察到较高的 R _S率，但这种影响的大小和持续时间取决于树种。我们建议气候季节性调节 R _S的响应氮的可用性，只有当环境条件合适时，树种的影响才会变得相关。2 月至 5 月和 9 月，松树下施肥地块中的R _S较大，而橡树下仅在 4 月观察到响应，这可能是由于每种树种下原生土壤化学计量的差异。总体而言，R _S在该地中海交错带地区的 3 年富氮过程中表现出高度稳定性。然而，我们观察到施氮事件后的短期土壤反应——碱性阳离子的丧失、土壤酸化和微生物生物量减少——这强调了如果长期持续富集氮对地下 C 和 N 循环的影响的必要性。