State Key Laboratory of Grassland Agro-Ecosystems, College of Ecology, Lanzhou University, Lanzhou, 730000, China; Center for Grassland Microbiome, College of Pastoral Agriculture Science and Technology, Lanzhou University, Lanzhou, 730000, China.
State Key Laboratory of Grassland Agro-Ecosystems, College of Ecology, Lanzhou University, Lanzhou, 730000, China.
Environ Res. 2022 Aug;211:113033. doi: 10.1016/j.envres.2022.113033. Epub 2022 Mar 8.
Legume-associated symbiotic diazotrophs contribute more to nitrogen (N) fixation than non-symbiotic diazotrophs in many terrestrial ecosystems. However, the percentage of legume biomass is low in alpine meadows on the Tibetan Plateau. Therefore, non-symbiotic diazotrophs may play important roles in N fixation in alpine meadow soils. Moreover, Tibetan alpine meadows are fragile and sensitive to global climate change, and the investigating of the key factor driving soil diazotrophic community still entails several challenges. To address these issues, we investigated diazotrophic spatial distribution and diversity along the elevational gradient between 3200 and 4200 m in the alpine meadow using amplicon sequencing of nifH gene. The result clearly showed that soil moisture and temperature were key factors driving soil diazotrophic community structures. Both altitude and soil depth significantly differentiated diazotrophic community composition. Alpha diversity indices of diazotrophic communities showed unimodal distribution along elevation gradient, strongly affected by soil moisture. Altitudinal niches were occupied by different diazotrophs. Soils at lower elevations were dominated by symbiotic diazotrophs and associative diazotrophs related to high biomass of plant hosts, while those at higher elevations were dominated by free-living psychrophiles such as Polaromonas. Furthermore, high moisture stimulated free-living anaerobes at middle elevations, such as Geobacter and Anaeromyxobacter, while suppressed legumes and symbiotic Mezorhizobium. Soil temperature not only directly affected temperature-sensitive diazotrophs, but also indirectly affected them through plants and soil properties such as pH and ammonium content. Our results suggest that climate change may strongly affect biological nitrogen fixation (BNF), and free-living diazotrophs may play important roles in BNF of alpine meadow system on the Tibetan Plateau.
豆科植物共生固氮菌比非共生固氮菌在许多陆地生态系统中贡献更多的氮（N）固定。然而，在青藏高原高寒草甸中，豆科植物的生物量比例较低。因此，非共生固氮菌可能在高寒草甸土壤氮固定中发挥重要作用。此外，青藏高原高寒草甸对全球气候变化非常脆弱和敏感，调查驱动土壤固氮生物群落的关键因素仍然存在一些挑战。为了解决这些问题，我们利用 nifH 基因扩增子测序技术，在海拔 3200 至 4200 米的高寒草甸沿海拔梯度调查了固氮生物的空间分布和多样性。结果清楚地表明，土壤水分和温度是驱动土壤固氮生物群落结构的关键因素。海拔和土壤深度都显著区分了固氮生物群落的组成。固氮生物群落的 alpha 多样性指数沿海拔梯度呈单峰分布，强烈受土壤水分的影响。固氮生物的生态位由不同的固氮生物占据。海拔较低的土壤主要由与植物宿主高生物量相关的共生固氮菌和共生固氮菌主导，而海拔较高的土壤则主要由自由生活的嗜冷菌如 Polaromonas 主导。此外，高水分在中海拔地区刺激了自由生活的厌氧菌，如 Geobacter 和 Anaeromyxobacter，而抑制了豆类植物和共生的 Mesorhizobium。土壤温度不仅直接影响对温度敏感的固氮生物，还通过植物和土壤特性（如 pH 值和铵含量）间接影响它们。我们的研究结果表明，气候变化可能会强烈影响生物固氮（BNF），自由生活的固氮生物可能在青藏高原高寒草甸系统的 BNF 中发挥重要作用。
