青藏高原横断山脉土壤理化与微生物的海拔变化特征

对青藏高原东南部三座雪山不同海拔梯度上采集的森林土壤样品进行的研究结果表明，土壤总氮（TN）和铵态氮（NH4+-N）在高海拔地区显著富集，这与青藏高原普遍存在的氮限制的观点相反。净矿化作用随海拔没有明显的变化趋势，而净硝化速在高海拔地区显著低于低海拔地区，且与 pH 值显著正相关（P < 0.001），与土壤水分显著负相关（P < 0.001），这造成了高海拔地区氮的稳定释放和低氮损失，从而大大促进了高山森林土壤高海拔地区氮的富集。此外，我们发现固氮速率沿海拔升显著增加，主要由高土壤有机碳驱动，大大有利于高海拔地区的氮素富集。此外，固氮微生物群落具有显著的海拔模式，耐酸性的 Bradyrhizobium、与植物相关的 Herbaspirillum 和 Klebsiella在高海拔地区显著富集，并与观察到的以冷杉为主要植被类型的高海拔地区的高固氮速率密切相关。

Results from forest soil samples collected along elevation gradients on three snow-capped mountains in southeastern Qinghai-Tibet Plateau demonstrate that soil total nitrogen (TN) and ammonium nitrogen (NH4+-N) were significantly enriched at high elevations, which contradicts the prevailing perspective of widespread nitrogen limitation across the Qinghai-Tibet Plateau. Net mineralization showed no significant trend along elevation gradients, while net nitrification rates were significantly lower at high elevations than at low elevations, and exhibited significant positive correlations with soil pH (P < 0.001) and significant negative correlations with soil moisture content (P < 0.001). This leads to stable nitrogen release and low nitrogen loss at high elevations, thereby substantially promoting nitrogen enrichment in alpine forest soils at high elevations. Additionally, we observed that nitrogen fixation rates increased significantly with increasing elevation, a pattern primarily driven by high soil organic carbon content, which greatly facilitates nitrogen enrichment at high elevations. Furthermore, nitrogen-fixing microbial communities displayed significant elevation distribution patterns: acid-tolerant Bradyrhizobium, plant-associated Herbaspirillum and Klebsiella were significantly enriched at high elevations, and were closely associated with the observed high nitrogen fixation rates in high-altitude regions where fir is the dominant vegetation type.