Li Chengyi, Valencia Enrique, Shi Yan, Zhou Guiyao, Li Xilai
College of Agriculture and Animal Husbandry, Qinghai University, Xining, China.
Departamento de Biodiversidad, Ecología y Evolución, Facultad de Ciencias Biológicas, Universidad Complutense de Madrid, Madrid, Spain.
Front Microbiol. 2023 Sep 15;14:1240634. doi: 10.3389/fmicb.2023.1240634. eCollection 2023.
Soil bacteria play a crucial role in the terrestrial nitrogen (N) cycle by fixing atmospheric N, and this process is influenced by both biotic and abiotic factors. The diversity of N-fixing bacteria (NFB) directly reflects the efficiency of soil N fixation, and the diversity of NFB in degraded alpine meadow soil may change with different N fertilizing levels and varied slopes. However, how N addition affects the diversity of NFB in degraded alpine meadows, and whether this influence varies with slope, remain poorly understood.
We conducted an N addition field experiment at three levels (2, 5, and 10 g N·m·a) to study the effects of N addition on soil NFB diversity on two different slopes in a degraded meadow on the Tibetan Plateau.
There were significant differences in the dominant bacterial species between the two slopes. The Chao1 index, species richness, and beta diversity of NFB did not differ significantly between slopes, but the Shannon index did. Interestingly, N addition had no effect on the diversity of NFB or the abundance of dominant bacteria. However, we did observe a significant change in some low-abundance NFB. The community composition and diversity of NFB were significantly positively correlated with slope and soil physicochemical properties (e.g., total potassium, pH, and total nitrogen).
Our study highlights the variation in NFB communities among different slopes in degraded alpine meadows and their resilience to exogenous N addition. Our results also underscore the importance of considering the effects of micro-topography on soil microbial communities in future studies of alpine ecosystems.
土壤细菌通过固定大气中的氮在陆地氮循环中发挥关键作用，这一过程受到生物和非生物因素的影响。固氮细菌（NFB）的多样性直接反映了土壤固氮效率，退化高寒草甸土壤中NFB的多样性可能会随不同的施氮水平和坡度而变化。然而，添加氮如何影响退化高寒草甸中NFB的多样性，以及这种影响是否随坡度而变化，目前仍知之甚少。
我们在青藏高原退化草甸的两个不同坡度上进行了三个水平（2、5和10 g N·m·a）的施氮田间试验，以研究施氮对土壤NFB多样性的影响。
两个坡度之间的优势细菌种类存在显著差异。NFB的Chao1指数、物种丰富度和β多样性在不同坡度间无显著差异，但香农指数有差异。有趣的是，添加氮对NFB的多样性或优势细菌的丰度没有影响。然而，我们确实观察到一些低丰度NFB有显著变化。NFB的群落组成和多样性与坡度和土壤理化性质（如全钾、pH值和全氮）显著正相关。
我们的研究突出了退化高寒草甸不同坡度间NFB群落的差异及其对外源添加氮的恢复力。我们的结果还强调了在未来高寒生态系统研究中考虑微地形对土壤微生物群落影响的重要性。
