Autotrophic and symbiotic diazotrophs dominate nitrogen-fixing communities in Tibetan grassland soils

Biological nitrogen fixation, conducted by soil diazotrophs, is the primary nitrogen source for natural grasslands. However, the diazotrophs in grassland soils are still far from fully investigated. Particularly, their regional-scale distribution patterns have never been systematically examined. Her...

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Bibliographic Details
Published in:The Science of the total environment 2018-10, Vol.639, p.997-1006
Main Authors: Che, Rongxiao, Deng, Yongcui, Wang, Fang, Wang, Weijin, Xu, Zhihong, Hao, Yanbin, Xue, Kai, Zhang, Biao, Tang, Li, Zhou, Huakun, Cui, Xiaoyong
Format: Article
Language:English
Subjects:
Biogeography
Biological nitrogen fixation
Grassland
MiSeq sequencing
Nitrogen
Nitrogen Fixation
Soil
Soil microbes
Soil Microbiology
Symbiosis - physiology
Tibet
Tibetan Plateau
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Summary:Biological nitrogen fixation, conducted by soil diazotrophs, is the primary nitrogen source for natural grasslands. However, the diazotrophs in grassland soils are still far from fully investigated. Particularly, their regional-scale distribution patterns have never been systematically examined. Here, soils (0–5 cm) were sampled from 54 grasslands on the Tibetan Plateau to examine the diazotroph abundance, diversity, and community composition, as well as their distribution patterns and driving factors. The diazotroph abundance was expressed as nifH gene copies, measured using real-time PCR. The diversity and community composition of diazotrophs were analyzed through MiSeq sequencing of nifH genes. The results showed that Cyanobacteria (47.94%) and Proteobacteria (45.20%) dominated the soil diazotroph communities. Most Cyanobacteria were classified as Nostocales which are main components of biological crusts. Rhizobiales, most of which were identified as potential symbiotic diazotrophs, were also abundant in approximately half of the soil samples. The soil diazotroph abundance, diversity, and community composition followed the distribution patterns in line with mean annual precipitation. Moreover, they also showed significant correlations with prokaryotic abundance, plant biomass, vegetation cover, soil pH values, and soil nutrient contents. Among these environmental factors, the soil moisture, organic carbon, available phosphorus, and inorganic nitrogen contents could be the main drivers of diazotroph distribution due to their strong correlations with diazotroph indices. These findings suggest that autotrophic and symbiotic diazotrophs are the predominant nitrogen fixers in Tibetan grassland soils, and highlight the key roles of water and nutrient availability in determining the soil diazotroph distribution on the Tibetan Plateau. [Display omitted] •Soil diazotrophs were studied across 54 grasslands on the Tibetan Plateau.•Cyanobacteria and Proteobacteria dominated the diazotroph communities.•Biological crust and symbiotic nitrogen fixation may serve as vital N sources.•Diazotroph abundance and diversity distributed according to mean annual precipitation.•Diazotroph distribution may be mainly driven by soil moisture and nutrient contents.
ISSN:0048-9697
1879-1026
DOI:10.1016/j.scitotenv.2018.05.238