Diversity and Variation of Asymbiotic Nitrogen-Fixing Microorganisms in Alpine Grasslands on the Tibetan Plateau

Abstract

Asymbiotic nitrogen-fixing (ANF) bacteria contribute a substantial amount of nitrogen in ecosystems, especially in those with low symbiotic nitrogen fixation (SNF) capability. Degradation of alpine grassland is widespread on the Tibetan Plateau and sown grassland has become one of the main strategies for grassland restoration. However, the diversity and community structure of ANF bacteria in different grassland types remain unknown. The aim of this study was to fill this gap. Soil samples were obtained from 39 grassland plots selected from three counties in the eastern Tibetan Plateau. The plots were classified as natural grassland (NG), sown grassland (SG), lightly degraded grassland (LDG), and severely degraded grassland (SDG). ANF microbial communities of the four grassland types were compared at the level of community and species diversity by 16S rRNA high-throughput sequencing technology. The phylum Proteobacteria accounted for >72% of the ANF bacteria. The community structures of soil ANF bacteria differed significantly (p < 0.01) among grassland types. We concluded that: (1) planting gramineous forage could possibly mitigate the decrease in diversity of soil ANF bacteria caused by grassland degradation; and (2) the diversity of soil ANF bacteria in alpine grassland of the Tibetan Plateau is closely related to grassland degradation and restoration.

Enhancing plant growth promoting rhizobacterial activities through consortium exposure: A review

“…Nitrogen is prominently present in the atmosphere in a gaseous form which is impassable to plants and animals. Assimilation of nitrogen by plants, atmospheric nitrogen is required to convert into ammonia, and this conversion is driven by nitrogenase enzymatic complex containing nitrogen-fixing microorganisms and the process called biological nitrogen fixation ( Li et al, 2021 ). Rhizobia is the universal group of bacteria to fix nitrogen which is abundantly present in the rhizospheric area of soil ( Shimonda et al, 2020 ).…”

Planting grass enhances relations between soil microbes and enzyme activities and restores soil functions in a degraded grassland

“…For example, pioneer plants ( Serianthes calycina and Gymnostoma webbianum ) regulated bacterial functional groups involved in the N-cycle in the Nickel mine soils ( Héry et al, 2005 ). Moreover, the effects of forage culture on microbial functional groups may drive the progress of grassland ecological restoration ( Fry et al, 2017 ; Li et al, 2021 ). A study showed that planting gramineous forage ( Elymus nutans ) increased the diversity and activity of asymbiotic nitrogen-fixing bacteria, which may promote soil function recovery and degraded grassland restoration ( Li et al, 2021 ).…”

“…Moreover, the effects of forage culture on microbial functional groups may drive the progress of grassland ecological restoration ( Fry et al, 2017 ; Li et al, 2021 ). A study showed that planting gramineous forage ( Elymus nutans ) increased the diversity and activity of asymbiotic nitrogen-fixing bacteria, which may promote soil function recovery and degraded grassland restoration ( Li et al, 2021 ). However, forage culture rapidly increases plant biomass, which may cause an increase in plant pathogen abundance, thus inhibiting plant growth and grassland restoration rates ( Kardol and Wardle, 2010 ).…”

“…Soil EEAs can reflect the activity of microbial-mediated soil functions ( Chodak and Niklińska, 2010 ; Liu et al, 2021 ). In grassland restoration, plants regulate soil microbial functional groups by releasing root exudates and degrading litter ( Steinauer et al, 2016 ; Li et al, 2021 ). Subsequently, microbial functional groups produce soil extracellular enzymes, and the activity of these enzymes is positively correlated with soil functions ( Liu et al, 2021 ).…”